Effect of Movement Pattern and Velocity of Strength Training

i

A thesis Submitted for the degree

Doctor of Philosophy

by

Anthony Blazevich, BSc (Hons)

School of Exercise Science and Sport Management

Southern Cross University, Lismore, Australia

2000.

EFFECT OF MOVEMENT PATTERN AND

VELOCITY OF STRENGTH TRAINING

EXERCISES ON TRAINING ADAPTATIONS

DURING CONCURRENT RESISTANCE AND

SPRINT/JUMP TRAINING

ii

DECLARATION

The work presented in this thesis is the original work of the author except where

acknowledged in the text. I hereby declare that I have not submitted this material

either in whole or in part for a degree at this or any other institution.

____________________ _________________

Anthony Blazevich.

iii

ACKNOWLEDGMENTS

I’d first of all like to acknowledge my supervisors Dr. Robert Newton and Assoc.

Prof. Roger Bronks who gave me the freedom to pursue my research interests

while keeping a firm watch over me. Their belief in my ability has given me the

confidence to complete my this thesis.

Assoc. Prof. Greg Wilson who brought me to Southern Cross University and

ensured that I remembered exactly what I was wanted to research and was not

only my first PhD supervisor, but also helped me through many tough times.

My fellow postgraduates, Nick Gill, Anthony Giorgi, Tony Shield, Adam

Bryant, Nathan Deans and Phil Smith who all at some point or another helped

me with my research and put up with my whingeing.

The School of Exercise Science and Sport Management for providing me with

the opportunity to develop my knowledge in the Sport Science field, and for

providing the funding for my research. Also, the American Society of

Biomechanics whose Student Grant-in-Aid progam jointly funded my research.

Mr. Terry Woods for having faith in my teaching and researching ability and

allowing me to teach while completing the final stages of my Thesis.

My parents, Ron and Yvonne, and my brother Michael for letting me know that

it wasn’t just OK, but obligatory for me to fulfil my ambition to become the best

sports scientist I could be even though I’d have to live as a student for many

years.

To all of the subjects, and my friends in Lismore, who so graciously gave their

time and effort to help me. Many of my subjects offered their time and support for

little personal reward, I will never forget that.

iv

To my genuine support staff Carol Hayllar, Sharee Mulcahy, Carol Hartmann,

Tiffeny Byrnes, Rob Baglin and Mark Fisher. They not only provided support

essential for me to complete my work, but to kept me sane when I was bordering

on insanity.

A final mention must also be made to two people who have been there for me

through both the tough times and the good, who provided inspiration and support

when I needed it, who counselled me when I was down, and were unselfishly

happy for me when I achieved. First, Nick Gill who was there from the beginning

to not only help me be the scientist I am today, but the person I am as well. No

one has accompanied me through more of a metamorphosis than him. And

second, Jen Goward for her care and constant belief in my ability, and also for

putting up with my constant mood swings.

v

PUBLICATIONS/PRESENTATIONS FROM THESIS

Blazevich, A.J. & Gill, N. (2001). Reliability and validity of two isometric squattests. Journal of Strength and Conditioning Research. In Press.

Conference Presentations

Blazevich, A.J.*, Newton, R.U. & Bronks, R. (2000). Podium Presentation -Movement specificity of muscle architectural changes after concurrent sprint/jumpand resistance training. The 2nd International Conference on Weightlifting andStrength Training, Ipoh Malaysia, 2000.

Blazevich, A.J.*, Bronks, R. & Newton, R.J. (2000). Movement specificity ofmuscle architectural changes after concurrent sprint/jump and resistancetraining.2000 Pre-Olympic Congress, Brisbane Australia, 2000.

Blazevich, A.J.*, Newton, R.U., Sharman, M., Bronks, R. & Gill, N. (2000).Specificity of Strength training exercises to the vertical jump and 20 m sprint tests.Australian and New Zealand Society of Biomechanics Conference, Gold CoastAustralia, 2000.

Blazevich, A.J.*, Newton, R.U., Bronks, R. & Gill, N. (1999). Influence ofmovement pattern of resistance training on athletic performance during concurrentresistance and task training. IOC World Congress in Sports Science, SydneyAustralia, 1999.

Blazevich, A.J.*, Newton, R.U., Sharman, M., Bronks, R. & Gill, N. (1999).Specificity of strength training exercises to the sprint run and vertical jump tests.IOC World Congress in Sports Science, Sydney Australia, 1999.

i

TABLE OF CONTENTS

DDEECCLLAARRAATTIIOONN ......................................................................................................................................IIII

AACCKKNNOOWWLLEEDDGGMMEENNTTSS ..........................................................................................................................IIIIII

PPUUBBLLIICCAATTIIOONNSS//PPRREESSEENNTTAATTIIOONNSS FFRROOMM TTHHEESSIISS ..................................................................................... VV

CONFERENCE PRESENTATIONS........................................................................................................ V

TTAABBLLEE OOFF CCOONNTTEENNTTSS............................................................................................................................. II

LLIISSTT OOFF FFIIGGUURREESS .................................................................................................................................VVII

LLIISSTT OOFF TTAABBLLEESS...................................................................................................................................IIXX

LLIISSTT OOFF AABBBBRREEVVIIAATTIIOONNSS .....................................................................................................................XXII

ABSTRACTS....................................................................................................................................... XIII

STUDY ONE: A COMPARISON OF MOVEMENT PATTERNS OF THE VERTICAL JUMP, BROAD JUMP AND

ACCELERATION PHASE OF THE SPRINT RUN TO THE SQUAT LIFT AND FORWARD HACK SQUAT

EXERCISES. ....................................................................................................................................XIV

STUDY TWO: RELIABILITY AND VALIDITY OF TWO ISOMETRIC SQUAT AND FORWARD HACK SQUAT

TESTS .............................................................................................................................................XVI

STUDY THREE: RELIABILITY OF UNILATERAL AND BILATERAL FORWARD HACK SQUAT TESTS XVII

STUDY FOUR: PERFORMANCE RELATIONSHIPS BETWEEN VERTICAL JUMP, SPRINT RUNNING AND

STRENGTH TRAINING EXERCISES: IMPLICATIONS FOR MOVEMENT SPECIFICITY ........................ XVIII

STUDY FIVE: NEUROMUSCULAR AND PERFORMANCE ADAPTATIONS TO SHORT-TERM CONCURRENT

RESISTANCE AND SPRINT/JUMP TRAINING. .....................................................................................XIX

11..11 IINNTTRROODDUUCCTTIIOONN .............................................................................................................................. 22

11..22 PPUURRPPOOSSEE ........................................................................................................................................ 55

11..33 SSIIGGNNIIFFIICCAANNCCEE OOFF SSTTUUDDYY................................................................................................................ 66

11..44 OOVVEERRVVIIEEWW OOFF SSTTUUDDIIEESS .................................................................................................................. 77

1.4.1 STUDY ONE ............................................................................................................................ 7

1.4.2 STUDY TWO............................................................................................................................ 7

1.4.3 STUDY THREE......................................................................................................................... 8

1.4.4 STUDY FOUR........................................................................................................................... 8

1.4.5 STUDY FIVE ............................................................................................................................ 8

11..55 LLIIMMIITTAATTIIOONNSS ............................................................................................................................... 1100

11..66 DDEELLIIMMIITTAATTIIOONNSS ............................................................................................................................ 1111

CHAPTER 2: LITERATURE REVIEW.............................................................................................. 12

2.1 INTRODUCTION ....................................................................................................................... 13

2.2 EFFECT OF RESISTANCE TRAINING MOVEMENT PATTERN ON TASK PERFORMANCE ............. 14

2.2.1 Body position ................................................................................................................................... 14

2.2.2 Joint angles and muscle lengths ......................................................................................................... 16

ii

2.2.3 Unilateral versus bilateral specificity ................................................................................................. 23

2.2.4 Type of contraction ........................................................................................................................... 25

2.2.5 Type of pre-contraction ..................................................................................................................... 26

2.2.6 Summary .......................................................................................................................................... 27

2.3 EFFECT OF RESISTANCE TRAINING MOVEMENT VELOCITY ON TASK PERFORMANCE ........... 28

2.3.1 Isokinetic, velocity-specific training studies ....................................................................................... 28

2.3.2 Isokinetic training effects on task performance................................................................................... 30

2.3.3 Free-weight, isotonic training studies................................................................................................. 30

2.3.4 Mechanisms contributing to velocity-specific strength changes........................................................... 32

2.3.5 Summary .......................................................................................................................................... 47

2.4 BENEFITS OF RESISTANCE TRAINING TO HIGH-SPEED TASK PERFORMANCE ......................... 48

2.4.1 Strength and mass of muscle and connective tissue ............................................................................ 48

2.4.2 Consequences of Resistance Training for High-speed Task Performance ............................................ 50

2.4.3 Summary .......................................................................................................................................... 51

2.5 IMPLICATIONS OF THE LITERATURE REVIEW ......................................................................... 52

CCHHAAPPTTEERR 33:: SSTTUUDDYY OONNEE............................................................................................................. 5544

AA CCOOMMPPAARRIISSOONN OOFF MMOOVVEEMMEENNTT PPAATTTTEERRNNSS OOFF TTHHEE VVEERRTTIICCAALL JJUUMMPP,, BBRROOAADD JJUUMMPP AANNDD

AACCCCEELLEERRAATTIIOONN PPHHAASSEE OOFF TTHHEE SSPPRRIINNTT RRUUNN TTOO TTHHEE SSQQUUAATT LLIIFFTT AANNDD FFOORRWWAARRDD HHAACCKK SSQQUUAATT

EEXXEERRCCIISSEESS........................................................................................................................................... 5555

3.1 INTRODUCTION ................................................................................................................. 55

3.2 METHODS............................................................................................................................ 57

3.2.1 Subjects............................................................................................................................................ 57

3.2.2 Overview.......................................................................................................................................... 58

3.2.3 Videography ..................................................................................................................................... 58

3.2.4 Description of movement tasks.......................................................................................................... 60

3.2.5 Analysis of video data....................................................................................................................... 65

3.2.6 Statistical Analysis............................................................................................................................ 69

3.3 RESULTS............................................................................................................................... 70

3.3.1 General Movement Descriptions........................................................................................................ 70

3.3.2 Comparisons of Task Movement Patterns .......................................................................................... 74

3.4 DISCUSSION ........................................................................................................................ 83

CHAPTER 4: STUDY TWO.................................................................................................................. 87

RREELLIIAABBIILLIITTYY AANNDD VVAALLIIDDIITTYY OOFF IISSOOMMEETTRRIICC SSQQUUAATT AANNDD FFOORRWWAARRDD HHAACCKK SSQQUUAATT TTEESSTTSS .................. 8888

4.1 INTRODUCTION ................................................................................................................. 88

4.2 METHODS............................................................................................................................ 90

4.2.1 Subjects............................................................................................................................................ 90

4.2.2 Testing ............................................................................................................................................. 90

4.2.3 Data analysis..................................................................................................................................... 93

4.3 RESULTS .............................................................................................................................. 93

4.3.1 Reliability of ISQ and IFHS .............................................................................................................. 93

iii

4.3.2 Validity of isometric measures .......................................................................................................... 94

4.4 DISCUSSION ........................................................................................................................ 96

4.4.1 Reliability and validity ...................................................................................................................... 96

4.4.2 Movement specificity ........................................................................................................................ 98

4.4.3 Practical applications ........................................................................................................................ 98

4.4.4 Future research ................................................................................................................................. 99

4.4.5 Conclusion...................................................................................................................................... 100

CHAPTER 5: STUDY THREE............................................................................................................ 101

RELIABILITY OF UNILATERAL AND BILATERAL FORWARD HACK SQUAT TESTS......................... 102

5.1 INTRODUCTION ............................................................................................................... 102

5.2 METHODS.......................................................................................................................... 103

5.2.1 Subjects.......................................................................................................................................... 103

5.2.2 Protocol .......................................................................................................................................... 104

5.2.3 Determination of testing loads ......................................................................................................... 104

5.2.4 Test contractions............................................................................................................................. 105

5.2.5 Data analysis................................................................................................................................... 105

5.3 RESULTS ............................................................................................................................ 106

5.4 DISCUSSION ...................................................................................................................... 107

CHAPTER 6: STUDY FOUR ......................................................................................................... 109

PPEERRFFOORRMMAANNCCEE RREELLAATTIIOONNSSHHIIPPSS BBEETTWWEEEENN VVEERRTTIICCAALL JJUUMMPP,, SSRRIINNTT RRUUNNNNIINNGG AANNDD SSTTRREENNGGTTHH

TTRRAAIINNIINNGG EEXXEERRCCIISSEESS:: IIMMPPLLIICCAATTIIOONNSS FFOORR MMOOVVEEMMEENNTT SSPPEECCIIFFIICCIITTYY ............................................... 111100

6.1 INTRODUCTION ............................................................................................................... 110

6.2 METHODS.......................................................................................................................... 112

6.2.1 Subjects.......................................................................................................................................... 112

6.2.2 Procedure ....................................................................................................................................... 112

6.2.3 Data Analysis ................................................................................................................................. 118

6.3 RESULTS ............................................................................................................................ 119

6.4 DISCUSSION ...................................................................................................................... 122

CHAPTER 7 – STUDY FIVE .............................................................................................................. 126

NNEEUURROOMMUUSSCCUULLAARR AANNDD PPEERRFFOORRMMAANNCCEE AADDAAPPTTAATTIIOONNSS TTOO SSHHOORRTT--TTEERRMM CCOONNCCUURRRREENNTT RREESSIISSTTAANNCCEE

AANNDD SSPPRRIINNTT//JJUUMMPP TTRRAAIINNIINNGG ............................................................................................................ 112277

7.1 INTRODUCTION ............................................................................................................... 127

7.1.1 Muscle Architecture........................................................................................................................ 128

7.1.2 Longitudinal Research..................................................................................................................... 129

7.2 METHODS.......................................................................................................................... 130

7.2.1 Subjects.......................................................................................................................................... 130

7.2.2 Protocol .......................................................................................................................................... 131

7.2.3 Testing ........................................................................................................................................... 133

7.2.4 Training.......................................................................................................................................... 142

iv

7.2.5 Data analysis................................................................................................................................... 146

7.3 RESULTS ............................................................................................................................ 148

7.3.1 Performance Changes with Training ................................................................................................ 148

7.3.2 Isokinetic Knee Extension Torque ................................................................................................... 149

7.3.3 Muscle Size and Architecture .......................................................................................................... 150

7.3.4 Electromyographic Changes............................................................................................................ 157

7.5 DISCUSSION ...................................................................................................................... 162

7.5.1 Performance Changes with Training ................................................................................................ 162

7.5.2 Body Position-specific Strength Changes......................................................................................... 164

7.5.3 Joint Angle-specific Strength Changes............................................................................................. 164

7.5.3 Laterality-specific Strength Changes................................................................................................ 166

7.5.4 Velocity-specific Isokinetic Torque Changes ................................................................................... 167

7.5.5 Changes in Muscle Architecture ...................................................................................................... 168

7.5.6 Muscle Recruitment Pattern Changes with Training ......................................................................... 173

7.5.7 Practical Implications...................................................................................................................... 176

CHAPTER 8: THEORY ON EARLY ADAPTATIONS TO RESISTANCE TRAINING ................ 179

8.1 DOCUMENTATION OF THEORY .............................................................................................. 180

8.1.1 Are strength changes related to muscle activation? ........................................................................... 180

8.1.2 How does muscle strength increase with resistance training? ............................................................ 182

8.1.3 How would muscle architecture affect strength?............................................................................... 183

8.1.4 Is there a neural explanation for angle-specific strength changes? ..................................................... 184

8.1.6 How does muscle strength increase in a velocity-specific manner?.................................................... 189

8.1.7 What about conflicts in architecture and fibre type?.......................................................................... 189

8.1.8 Conclusion...................................................................................................................................... 191

8.2 ‘PERIPHERAL ADAPTATIONS’ EXAMPLE OF STRENGTH CHANGES AFTER RESISTANCE EXERCISE.

..................................................................................................................................................... 191

8.2.1 What adaptations are likely in the first week of training? .................................................................. 192

8.2.2 What about muscle activation? ........................................................................................................ 196

8.2.3 What about general strength increases?............................................................................................ 197

8.2.4 Long-term adaptations?................................................................................................................... 198

8.3 SUMMARY ............................................................................................................................. 198

CHAPTER 9: THESIS SUMMARY................................................................................................... 200

9.2 FUTURE RESEARCH ............................................................................................................... 205

REFERENCES..................................................................................................................................... 206

AAPPPPEENNDDIIXX AA...................................................................................................................................... 224499

ETHICS APPLICATION.................................................................................................................. 249

BIOMECHANICAL AND CROSS-SECTIONAL ANALYSIS OF FOUR RESISTANCE TRAINING EXERCISES

..................................................................................................................................................... 249

AAPPPPEENNDDIIXX BB...................................................................................................................................... 225577

v

ETHICS APPLICATION.................................................................................................................. 257

INFLUENCE OF MOVEMENT PATTERN OF RESISTANCE TRAINING EXERCISES ON VERTICAL JUMP

AND SPRINT RUNNING PERFORMANCE DURING CONCURRENT RESISTANCE AND TASK TRAINING ... 257

AAPPPPEENNDDIIXX CC...................................................................................................................................... 227700

STATEMENT OF INFORMED CONSENT .......................................................................................... 270

RELIABILITY AND VALIDITY OF ISOMETRIC SQUAT AND FORWARD HACK SQUAT TESTS .............. 270

AAPPPPEENNDDIIXX DD...................................................................................................................................... 227744

TRAINING PROGRAMS ................................................................................................................. 274

EXAMPLE RESISTANCE TRAINING PROGRAMS FOR SQ (SQUAT) AND FHS (FORWARD HACK SQUAT)

GROUPS......................................................................................................................................... 274

AAPPPPEENNDDIIXX FF ...................................................................................................................................... 227777

RELIABILITY STUDY .................................................................................................................... 277

A COMPARISON OF DIGITAL CURVIMETER AND MATHEMATICAL ESTIMATES OF FASCICLE LENGTH

IN CONTRACTING MUSCLE. ........................................................................................................... 277

AAPPPPEENNDDIIXX GG ..................................................................................................................................... 229966

FORWARD HACK SQUAT DATA COLLECTION SCHEMATIC............................................................ 296

vi

LIST OF FIGURES

Figure 3.1a. The forward hack squat (FHS) exercise was performed in

a semi-prone position by first lowering a sled until the internal knee

angle was approximately 100o................................................................... 64

Figure 3.1b. After lowing the sled it was then moved back to the

starting position in preparation for the next repetition................................ 64

Figure 3.2. The single-leg forward hack squat was performed as per the

double-leg version except that the ‘free’ leg was extended behind the

body in the descending phase and then flexed in the ascending phase.... 65

Figure 3.3. A bar extension was placed on the weighted bar.................. 67

Figure 3.4. Movement pattern of the squat lift exercise........................... 71

Figure 3.5. Movement pattern of the forward hack squat (FHS)

exercise...................................................................................................... 71

Figure 3.6. Movement pattern of the vertical jump................................... 73

Figure 3.7. Movement pattern of the broad jump..................................... 73

Figure 3.8. Comparison of the jump-squat (JSQ) and squat lifts with

60% (SQ + 60%) and 140% (SQ + 140%) of bodyweight across the

shoulders................................................................................................... 75

Figure 3.9. Comparison of single-leg forward hack squat (FHS 1L) and

forward hack squats with 60% (FHS + 60%) and 100% (FHS + BW) of

bodyweight added to the sled.................................................................... 75

Figure 3.10. Comparison of the vertical jumps with arms across the

chest (VJ ac) and with arm swing (VJ wa)................................................. 77

Figure 3.11. Comparison of single-leg broad jump (BJ 1L), broad jump

with arms across the chest (BJ ac) and broad jump with arm swing (BJ

wa)............................................................................................................. 77

Figure 3.12. Comparison of the vertical jump with arms across chest

(VJ ac) and jump-squat (JSQ)................................................................... 79

vii

Figure 3.13. Comparison of forward hack squat with a load equal to

bodyweight added to the sled (FHS + BW) and broad jump with arms

across the chest (BJ ac)............................................................................ 79

Figure 3.14. Comparison of vertical jumps with arm swing (VJ wa) and

vertical jumps with arms across chest (VJ ac)........................................... 80

Figure 3.15. Comparison of the jump-squat (JSQ) and vertical jump

with arms across chest (VJ ac).................................................................. 81

Figure 3.16. Comparison of joint angle changes for the forward hack

squat (FHS) and acceleration phase of a sprint run (adapted from

Jacobs & Ingen Schenau, 1992)................................................................ 82

Figure 4.1. Subject position for both the isometric squat and forward

hack squat tests......................................................................................... 89

Figure 4.2. Scatterplots of isometric versus 1-RM test performance....... 96

Figure 6.1. Body position for VJ showing cable (to position transducer)

and belt...................................................................................................... 114

Figure 6.2. Position for isometric squat test............................................. 115

Figure 6.3. Position for the isometric forward hack squat (IFHS)............ 117

Figure 6.4. Scatterplots of isometric force produced during a squat

(Squat force isom.) and force during a squat with a load of 60% of

maximum isometric load (Squat force 60%) against VJ height....... 120

Figure 6.5. Scatterplots of isometric force produced during a forward

hack squat (FHS isom.) and force during a FHS with a load of

40% of maximum isometric load (FHS force 40%) against 20 m

sprint time........................................................................................ 122

Figure 7.1. Overview of training and testing............................................. 132

Figure 7.2. The muscle-tendon juntion of rectus femoris was

determined by moving the scanning head (ultrasound) distally along the

thigh........................................................................................................... 136

Figure 7.3. Muscle thickness, pennation and fascicle length estimates

were made at two sites of the rectus femoris and vastus lateralis muscle

using ultrasound......................................................................................... 137

Figure 7.4. Single-leg forward hack squat................................................ 142

viii

Figure 7.5. Change in muscle thickness for all muscle sites.................... 152

Figure 7.6. Change in muscle pennation for all muscle sites................... 154

Figure 7.7. Change in fascicle length for all muscle sites........................ 176

Figure 7.8. Change (±95% CI) in normalised EMG for five thigh

muscles during the acceleration phase of a sprint run............................... 159

Figure 7.9. Change (±95% CI) in normalised EMG for five thigh

muscles during the performance of a vertical jump................................... 161

Figure 8.1. Hypothesised time course of muscular (A) and neural (B)

changes with resistance exercise.............................................................. 199

ix

LIST OF TABLES

Table 2.1. Myosin Heavy Chain isoforms in human skeletal muscle........ 42

Table 2.2. Contractile protein isoforms (not including MHC) in human

skeletal muscle......................................................................................... 43

Table 3.1. Landmark names and marker positions for reflective

markers..................................................................................................... 59

Table 3.2. Camera settings during data acquisition................................ 60

Table 3.3. Description of vertical jump techniques.................................. 61

Table 3.4. Description of broad jump techniques.................................... 62

Table 3.5. Body segment definitions....................................................... 66

Table 3.6. Joint angle definitions............................................................. 66

Table 4.1. Reliability statistics for ISQ and IFHS..................................... 94

Table 4.2. Pearson’s correlations for test performances......................... 95

Table 5.1. Mean (±SD) force produced during each trial......................... 106

Table 5.2. Reliability statistics for force produced during dynamic

forward hack squat trials........................................................................... 107

Table 6.1. Mean performance (±SD) for those variables selected for

analysis..................................................................................................... 119

Table 6.2. Significant correlation coefficients (p<0.01) for performance

data........................................................................................................... 120

Table 6.3. Results of factor analysis........................................................ 121

Table 7.1. Details of electrode placements on the five thigh muscles..... 140

Table 7.2. Pre-training, post-training and change scores for sprint, VJ,

FHS and SQ tests..................................................................................... 148

Table 7.3. Reliability statistics for angle of peak torque.......................... 149

Table 7.4. Angle of peak torque (0o = full extension) pre- and post-

training...................................................................................................... 150

Table 7.5. Mean (±SD) pre- and post-test muscle thickness and

change in thickness.................................................................................. 151

x

Table 7.6. Mean (±SD) pre- and post-test muscle pennation and

change in pennation.................................................................................. 153

Table 7.7. Mean (±SD) pre- and post-test estimated fascicle length and

change in fascicle length........................................................................... 155

Table 7.8. Results of correlation analysis on pennation and estimated

fascicle length changes after training........................................................ 157

xi

LIST OF ABBREVIATIONS

Abbreviation Description

1-RM One repetition maximum

A/D Analog to digital conversion

APT Angle of peak torque (isokinetic)

BF Biceps femoris

BJ Broad jump

BJ 1L Broad jump with one leg (unilateral BJ)

BJ ac Broad jump with arms crossed over the chest

BJ wa Broad jump with arm swing

BW Body weight

C7 7th Cervical vertebra

CI Confidence interval (95%)

EMG Electromyography

ES Effect size statistic

FHS Forward hack squat exercise, or a group of subjects who

performed forward hack squat training

FHS 1L Forward hack squat with one leg (unilateral FHS)

FL Fascicle length

FM Fictional muscle

GL Gluteus maximus

HF Hip flexor (superficial to psoas major muscle)

ICC Intra-class correlation coefficient

IFHS Isometric forward hack squat

ISQ Isometric squat

JSQ Jump squat

MU Motor unit

RF Rectus femoris

RF d Distal rectus femoris

RF p Proximal rectus femoris

xii

RT Resistance training

SD Standard deviation

SEE Standard error of the estimate (measure of error in regression)

SJ Sprint/jump group, a group of subjects who performed sprint and

jump training but no resistance training

SQ Free-weight barbell squat lift, or a group of subjects who

performed squat training

T Thickness of a muscle

TMJ Temporomandibular joint

VJ Vertical jump (countermovement)

VJ 1L Vertical jump with one leg (unilateral VJ)

VJ ac Vertical jump with arms crossed over the chest

VJ wa Vertical jump with arm swing

VL Vastus lateralis

VL d Distal vastus lateralis

VL p Proximal vastus lateralis

xiii

AABBSSTTRRAACCTTSS

xiv

STUDY ONE: A COMPARISON OF MOVEMENT PATTERNS OF THE

VERTICAL JUMP, BROAD JUMP AND ACCELERATION PHASE OF THE

SPRINT RUN TO THE SQUAT LIFT AND FORWARD HACK SQUAT

EXERCISES.

The first purpose of this study was to describe and compare the movement

patterns of athletic subjects performing vertical jump (VJ), standing broad jump

(BJ), squat lift (SQ) and jump-squat (JSQ) tasks. The term ‘movement pattern’

will be used to describe the timing and magnitude of joint angle changes (with

reference to angular velocities and accelerations), body position and laterality of a

movement. A second purpose was to compare the movement patterns of a new

exercise, named the forward hack squat (FHS), and the acceleration phase of a

sprint run. Eight athletic, weight-trained male subjects (age [±SD] = 25.1 ± 2.5

yrs, height = 1.81 ± 0.09 m, weight = 96.3 ± 10.0 kg) performed a standard warm-

up including five minutes of stationary cycling at a self-selected workload and

three to five trials each of a VJ, BJ, SQ with a load of 60% of bodyweight and FHS

with no load added to the sled (the FHS is described later). After reflective

markers were placed on joint centres of the head, trunk and limbs, subjects

performed three maximal trials of single- and double-leg vertical and standing

broad jumps with their arms in different positions, squat lifts and jump-squats with

different loads, and single- and double-leg FHS with different loads. The

movements were recorded by a high-speed video system (200 Hz) and data sets

relating to joint movement (joint angular displacement, velocity and acceleration)

were calculated after digitising joint markers using Peak Motus software (Peak

Performance Technologies, USA).

For all exercises studied, the timing of joint angle changes was the same during

the descending phase with hip, knee and ankle joints flexing (dorsiflexion at the

ankle) simultaneously. However, joint extension during the ascending phase was

different between the tasks. Joint extension occurred sequentially for the VJ, BJ

and JSQ exercises with hip extension preceding both knee and ankle

xv

(plantarflexion) extension. For the slower squat lifts (SQ) joint extensions

occurred simultaneously. The FHS was performed differently to these however in

that hip and knee extension occurred simultaneously with ankle plantarflexion

delayed. The use of an arm swing during VJ and BJ exercises caused the hip

angle to become smaller (more closed) at the end of the transition phase possibly

allowing greater use of the larger hamstring, gluteal and erector muscles. VJ’s

performed without arm swing exhibited the same joint changes as the JSQ

exercise but there were differences in hip joint range of motion between the two

exercises when the arms used.

From these results it was concluded that the joint angle changes of subjects

performing the VJ without arm swing were similar to that of the JSQ. The two

tasks are also performed bilaterally and in a vertical body position, thus their

movement patterns can be considered comparable. However the movement

patterns of the BJ and FHS were dissimilar with the timing of joint angle changes

being different. Joint angle changes for the FHS were then compared to

published data for the acceleration phase of sprint running (Jacobs & Ingen

Schenau, 1992). There was good agreement in the timing and magnitude of joint

angle changes for these two tasks. Given both exercises are performed with the

body in a semi-prone position and the FHS can be performed unilaterally, the

movement patterns of these two exercises could also be considered comparable.

xvi

STUDY TWO: RELIABILITY AND VALIDITY OF TWO ISOMETRIC SQUAT

AND FORWARD HACK SQUAT TESTS

Given the results of Study One, the FHS and SQ exercises were chosen for use in

training and testing in this thesis. However, performing 1-RM tests for the

purposes of assessing performance or designating training loads can be a long

process. It would therefore be ideal to use simpler isometric tests for these

purposes. The aim of this study was first to examine the reliability of isometric

squat (ISQ) and isometric forward hack squat (IFHS) tests to determine if

repeated measures on the same subjects yielded reliable results, and second to

examine the relationship between isometric and dynamic measures of strength to

assess validity. Fourteen male subjects (age range = 19 – 26 yrs) performed

maximal ISQ and IFHS tests on two occasions and 1-RM SQ and FHS tests on

one occasion. The two tests were found to be highly reliable (ICCISQ = 0.97 and

ICCIFHS = 1.00). There was a strong relationship between average ISQ and 1-RM

squat performance, and between IFHS and 1-RM FHS performance (rSQ = 0.77,

rFHS = 0.76; p<0.01) but a weak relationship between squat and FHS test

performances (r<0.55). There was also no difference between observed 1-RM

values and those predicted by our regression equations. Errors in predicting 1-

RM performance were in the order of 8.5% (SEE = 13.8 kg) and 7.3% (SEE =

19.4 kg) for ISQ and IFHS respectively. Correlations between isometric and 1-RM

tests were not of sufficient size to indicate high validity of the isometric tests.

Together the results of the present study suggest that ISQ and IFHS tests could

detect small differences in multi-joint isometric strength between subjects, or

performance changes over time, and that the scores in the isometric tests are well

related to 1-RM performance. However, there was a small error when predicting

1-RM performance from isometric performance so these tests probably cannot

discriminate between small changes in dynamic strength. The weak relationship

between squat and FHS test performance can be attributed to differences in the

movement patterns of the tests.

xvii

STUDY THREE: RELIABILITY OF UNILATERAL AND BILATERAL

FORWARD HACK SQUAT TESTS

The purpose of this study was to examine the reliability of complex, dynamic

unilateral and bilateral FHS tests and determine whether the loads lifted during the

tests affected their reliability. Eleven active, male subjects (age = 20.5 ± 1.1 yrs)

performed two maximal repetitions of a FHS at each of two loads (loads equal to

40% and 70% of maximal isometric force were added to the sled of the machine)

in both uni- and bilateral conditions. Reliability of both uni- and bilateral tasks was

high (ICC = 0.90 and 0.95 respectively) when the heavier load was lifted (70% of

isometric maximum). However, when the load was lighter (40% of isometric

maximum) reliability was low (ICC = 0.70 and 0.64 for unilateral and bilateral trials

respectively). Thus, while the laterality of movement did not affect task reliability,

the load lifted did. The most likely explanation for this result is that the greater

load promotes greater kinaesthetic feedback from muscle spindles, golgi tendon

organs and pacinian corpuscles to the spinocerebellum. In addition, subjects

displayed a bilateral deficit; a phenomenon that has been shown in past research.

This result indicates that the uni- and bilateral tests were measuring different

entities. Thus, testing should be performed according to the type of strength that

must be measured (unilateral or bilateral).

xviii

STUDY FOUR: PERFORMANCE RELATIONSHIPS BETWEEN VERTICAL

JUMP, SPRINT RUNNING AND STRENGTH TRAINING EXERCISES:

IMPLICATIONS FOR MOVEMENT SPECIFICITY

The results from Study One suggested that two pairs of tasks, 1) JSQ and VJ

(with arms crossed over the chest), and 2) FHS and acceleration phase of a sprint

run, were comparable in their movement patterns. The purpose of this study was

to investigate the relationship between subjects’ performances in tests of these

exercises to determine whether movement pattern alone determined performance

similarities between tasks. Thirty-one active subjects including 23 men and eight

women who volunteered from the University population (age range = 18 - 26 yrs)

performed sprint run (20 m), VJ, SQ and FHS tests. Relationships between

subjects’ performances were investigated by both correlation and components

analysis.

Subjects who performed well in the SQ and JSQ tests did not necessarily perform

well in the VJ tests relative to other subjects. However, the FHS and sprint tests,

and the ISQ and VJ tests, were significantly correlated (r = 0.51 – 0.73; p<0.01).

The components (from factor analysis) associated with the VJ and SQ tests, and

the FHS and sprint tests, were different; components could be described by the

force-velocity characteristics of the test exercises. The FHS and sprint tests were

however more similar based on the components under which they were placed.

The FHS may therefore be considered functionally similar to the acceleration

phase of a sprint run when tested under the conditions presented here.

Furthermore, as subjects who performed well in the ISQ also performed well in the

VJ, the two tasks must have some functional similarity. The ISQ requires high

muscle forces over small ranges of motion for optimum performance while high

forces at the eccentric/concentric (downward/upward) transition point in the VJ is

also important. Therefore, the movement pattern and ‘neuromuscular intent’ of

the exercises, but not necessarily their velocity, may have contributed to their

movement specificity. The results have implications for our understanding of

movement specificity.

xix

STUDY FIVE: NEUROMUSCULAR AND PERFORMANCE ADAPTATIONS

TO SHORT-TERM CONCURRENT RESISTANCE AND SPRINT/JUMP

TRAINING.

Given that, for most athletes, resistance training forms only part of a total training

program, it is important that adaptations to resistance training (RT) are described

when task training is performed concurrently. The purpose of this study was first

to determine whether changes in VJ and sprint running test performances after a

period of concurrent resistance- and sprint/jump training were related to the

movement pattern of RT exercises in well-trained subjects. From the results of

studies one and two, and given the known specificity of adaptations to resistance

training, one might expect that subjects who perform JSQ training would improve

their VJ, while subjects who perform FHS training would improve their sprint, more

than other subjects. A second purpose was to examine changes in the

neuromuscular system when the RT was performed concurrently with VJ and

sprint/jump training.

30 active individuals volunteered from the University population (Age range = 18 –

26 yrs). Of the 30 subjects, 23 (eight women & 15 men) completed the study with

approximately equal numbers of subjects in each of three training groups

(described below). Subjects participated in four weeks of resistance- and

sprint/jump training (familiarisation) prior to a second five-week (specific) training

phase.

Following the four-week familiarisation phase, subjects were divided into three

Familiarisation(4 weeks)

Pre-test Specific training (5 weeks)Four groups: SQ, FHS & SJ

Post-test

Overview of training and testing. A familiarisation phase preceded the five-week‘specific’ training phase. Testing was performed before and after the specific trainingphase.

xx

training groups with male and female subjects distributed equally among the

groups. These groups were labelled squat (SQ), forward hack squat (FHS) and

sprint/jump (SJ) based on their training. All groups performed at least two

sprint/jump sessions per week with SQ and FHS groups also performing two

weight training sessions and SJ two additional sprint/jump sessions each week.

Before and after the five-week specific training phase, subjects performed 20 m

sprint, VJ, SQ, FHS and isokinetic leg extension tests. In addition to these

performance tests, muscle thickness, pennation and fascicle length were

measured at two regions of both the vastus lateralis (VL) and rectus femoris (RF)

muscles and EMG was recorded from leg musculature during performance of VJ

and sprint tasks.

After training, subjects significantly increased their 10 m sprint (p<0.05), single-

and double-leg isometric FHS force (p<0.01), force during a double-leg FHS at

40% of isometric maximum, and force during a squat at 30% of isometric

maximum (p<0.05). However, there were no significant differences between the

training groups. This suggests that the five-weeks of training was sufficient to

cause performance changes, but that the training did not result in inter-group

differences. There was also no difference in isokinetic knee extension torque at

either 30o.s-1 or 180o.s-1 but there was a trend toward SQ subjects producing their

torque at a more closed knee angle compared to FHS (ES = 0.71) and SJ (ES =

0.90) subjects. Thus there was a trend toward angle-specific torque changes with

the angle of peak torque decreasing for SQ subjects but increasing for FHS

subjects.

Muscle architectural changes were different between the training groups. In

general, subjects who performed resistance training (SQ and FHS) showed

greater pennation and shorter fascicle lengths (used as an estimate of fibre

length) in VL, while the opposite was true for SJ subjects. For RF, pennation

increased at the distal region in FHS and SQ subjects (p<0.05), but there were no

changes at the proximal region and no significant changes in fascicle length in any

group. Thus for the uni-articular VL architectural adaptations occurred in line with

xxi

those hypothesised. The lack of change in RF might be related to its biarticular

action, muscle length changes are not as great in many multi-joint movements so

the stimulus for adaptation would have been small (Jacobs et al., 1993). There

were significant increases in muscle thickness of both VL and RF although these

changes were not significantly different between the groups. Therefore the

different training regimes performed by the subjects did not differently affect their

muscle thickness.

Changes in normalised EMG during the acceleration phase of running were

inconsistent between subjects. SQ and FHS subjects (results were pooled for

these subjects to increase statistical power) exhibited greater gluteus maximus

activation during the recovery part of the stride and greater biceps femoris, vastus

lateralis and rectus femoris activity immediately prior to foot-ground contact. Such

changes may not be conducive to efficient running. There were few changes for

SJ subjects. For VJ, decreased activity of rectus femoris in the descending phase

and increased gluteus maximus in the transition phase in SQ and FHS subjects

were hypothesised to aid jump efficiency and power. Again there were few

changes in the EMG of SJ subjects. Thus RT appeared to influence EMG and

therefore possibly inter-muscular coordination, particularly in SQ and FHS

subjects. There were however no significant changes in muscle co-contraction

during the sprint or changes in muscle onset times (i.e. time at which muscle

activity significantly increased) during the VJ.

The results of this study suggest that VJ, sprint and strength changes to short-

term concurrent training are not as specific to training as when RT is performed

alone. There were no significant differences in changes in strength, VJ and sprint

performance, and few changes in isokinetic test variables between the groups.

There were however significant changes in muscle architecture that appeared

related to the training performed by subjects. Furthermore, although the EMG

recordings do not provide conclusive evidence that inter-muscular coordination

changed with training, some changes were seen. It appears that, at least in the

short term, similar gains in strength and speed can be attained by different training

xxii

regimes. However there were significant muscular, and evidence for neural,

adaptations to the training. Thus, perhaps in the long-term, the movement pattern

of training exercises and the proportion of low-velocity strength training in a

regime might affect athletic performance and this should be followed up in future

training studies.

1

CCHHAAPPTTEERR 11:: DDeevveellooppmmeenntt ooff

tthhee PPrroobblleemm

2

1.1 INTRODUCTION

Resistance training (RT) is an important component of training for athletes who

require speed, power or strength to successfully compete in their sport. For

example, many sprint runners perform resistance exercises concurrently with their

running training to improve their speed and maximal power. However, which

resistance training exercises elicit optimum improvements in task performance is

yet to be determined (the term ‘task’ refers to the movement which is the focus for

improvement, for example a sporting movement such as running or jumping).

Evidence suggests that adaptations to training are movement-specific, thus some

authors predict that RT exercises best improve movements when they are similar

to the training exercise (Abernethy et al., 1994; Lindh, 1979; Rutherford et al.,

1986; Thépaut-Mathieu et al., 1988).

Movement specificity encompasses both movement pattern- and velocity-specific

adaptations to training. That is, an exercise may mimic or replicate the ranges of

motion, body positions and types of contraction of a movement (i.e. movement

pattern) and/or mimic the velocity of a movement. Thus, movement-specific

adaptations refer to the neuromuscular and performance adaptations to an

exercise of a specific movement pattern and velocity.

With respect to movement pattern specificity, it has been shown that adaptations

to RT depend on several ‘factors’. These include the body position adopted

(Raasch & Morehouse, 1957; Wilson et al., 1996), the muscle lengths and joint

angles through which work is performed (Kitai & Sale, 1989), whether training is

performed unilaterally or bilaterally (Tanaguchi, 1997) and the types of

contractions and precontractions used (e.g. eccentric, concentric, isometric, rapid

pre-stretch, etc.; Hortobágyi et al., 1996; 2000) during training. The mechanisms

responsible for such training effects are unclear. Evidence from research

investigating a neural basis for movement pattern specificity is contradictory in its

conclusions (i.e. changes in muscle co-contraction and timing of muscle

3

recruitment, e.g. Weir et al., 1994, 1995b) while little research has examined

muscular changes such as sarcomere length-tension characteristics (Koh, 1995).

From a more practical standpoint, research investigating movement pattern-

specific adaptations to RT has proffered as many questions as it has answered.

For example, it is unclear how similar movement patterns of a task must be to a

resistance exercise for optimum improvement, whether the movement patterns of

resistance exercises must be similar to the sporting task when both resistance-

and task training are being performed concurrently in a training regime, and

whether it is necessary to consider all factors of movement pattern specificity for

optimal improvements in sporting performance. Moreover, most studies

investigating movement pattern-specific adaptations to RT have used untrained or

‘active’ subjects (e.g. Delecluse et al., 1995; Narici et al., 1989; Sleivert et al.,

1995; Young & Bilby, 1993). Given that the propensity for adaptation of well-

trained or elite athletes could be different to that of untrained individuals (Häkkinen

et al., 1987) the results of research using untrained subjects may not predict the

adaptation process of well-trained athletes. Thus, research involving well-trained

subjects is necessary to establish the necessity for movement pattern-specific

resistance training when task training is performed concurrently. It is also

necessary to determine whether some ‘factors’ affecting movement pattern-

related adaptations are more important than other factors.

With respect to the velocity specificity of adaptations to RT, results of studies

investigating responses to isokinetic training suggest that strength increases are

greater at, and perhaps below, the movement velocities of the training exercises

(Caiozzo et al., 1981; Petersen et al., 1989). When an isotonic (isoinertial)

training mode is used, subjects who trained using higher-velocity movements

tended to perform better in tasks requiring higher movement speeds (Wilson et al.,

1993). These velocity-specific adaptations have been considered a reflection of

many neuromuscular changes. Changes in the nervous system are thought to

include increases in total muscle recruitment (Häkkinen and Komi, 1983, 1985,

1986; Häkkinen et al., 1985b), an increase in the firing frequency of motor units

4

(Behm & Sale, 1993b), a selective activation of fast-twitch fibres (Grimby &

Hannerz, 1977; Nardone et al., 1989) which may be more likely during the

performance of complex movements (Behm & Sale, 1993b), and the selective

recruitment of muscles containing a high fast-twitch fibre content (Duchateau et

al., 1986; Nardone & Schieppati, 1988). Muscular changes might include fibre

type transformation toward fast-twitch fibres (Jansson et al., 1990), changes in

sarcomere contractile kinetics (Behm & Sale, 1993b), and increases in muscle

fibre length (Sacks & Roy, 1982; Kumagai et al., 2000).

Despite research showing movement-specific adaptations to RT, many athletes

who perform resistance training concurrently with training for their own sport (task

training) use resistance training exercises of low movement velocities that are

often not similar in movement pattern to the task they wish to improve. Such

training methods are a result of anecdotal evidence from coaches and athletes

that good improvements in task performance are achieved by increasing ‘general’

strength by resistance training and then ‘transferring’ the strength by performing

task training. Furthermore, adaptations to resistance training have been reported

to have both a positive (Bell et al., 1989; Smith & Melton, 1981; Wilson et al.,

1996) and negative (Barrata et al., 1988; Behm & Sale, 1993b; Tesch & Larson,

1982) impact on high-speed task performance. As such it is unclear whether

resistance training, even at higher movement velocities, is beneficial to athletes

requiring high-velocity force production despite its accepted use as a training tool.

In summary, adaptations to resistance training appear to be specific to both the

movement pattern and velocity of the training exercises. Furthermore, some

research has highlighted possible disadvantages of weight training even when its

movement characteristics are similar to the sporting task. Given the disparity

between the ‘theoretically correct’ movement-specific resistance training and that

often performed by athletes, more research is needed to determine whether

resistance training is a useful addition to a training regime and whether the

movement characteristics of the resistance training must be similar to the sporting

task for optimum improvements to occur.

5

1.2 PURPOSE

There are a number of specific aims of this thesis:

1. To examine the movement patterns of the squat lift (SQ) and forward hack

squat (FHS; a new exercise) exercises in order to describe the body position,

joint angle changes and the timing of these changes, and laterality. Then

compare these to the movement patterns of the vertical jump (VJ), broad jump

(BJ) and sprint start (the technique used during the running acceleration phase

of sprinting).

2. To determine the reliability of isometric forward hack squat (IFHS) and squat

(ISQ) tests and their relationship to a dynamic (1-RM) versions of the same

exercise. This information will be used to determine whether isometric

versions of the exercises can be performed to estimate subject’s dynamic 1-

RM’s and predict training loads for a longitudinal (training) study.

3. To assess the reliability of uni-lateral and bilateral FHS tests under different

loading conditions.

4. To investigate the relationship between VJ and 20 m sprint performance and

the forces produced during maximal SQ and FHS lifts in a cross-sectional

analysis using well-trained athletes.

5. To examine the effects of different resistance training exercises on sprint and

jump performance in athletes who perform identical running acceleration and

VJ training.

6. To identify neuromuscular changes that are responsible for movement pattern-

and velocity-specific adaptations to concurrent resistance and task training.

7. To formulate a theory that can explain the adaptation process of the

neuromuscular system to concurrent resistance and task (e.g. VJ, sprint, etc.)

training using evidence gained from this research to substantiate some parts of

that theory.

6

1.3 SIGNIFICANCE OF STUDY

While research has shown that adaptations to RT are specific to the movement

pattern adopted, it is not yet clear which components of a task’s movement

pattern should be replicated when performing RT to achieve optimal improvement

in that task: body position, muscle lengths and joint angles, laterality (i.e. left limb,

right limb or both trained simultaneously), type of contraction, or type of pre-

contraction. It is also unclear whether the velocities of RT movements need to

approach task velocity and whether adaptations to RTare still specific to both

movement pattern and velocity when RT is combined with task training. This

contention is largely due to the majority of research examining the adaptations to

resistance training in subjects who are not performing task training concurrently.

This research will provide an insight into the importance of replicating body

position, joint angle changes and laterality (types of contraction and pre-

contraction will be similar between the RT and task movement patterns so their

effects cannot be evaluated) during RT for optimum improvement in dynamic task

performance. Furthermore, the adaptations that occur when RT is performed with

task training (the term ‘task’ refers to the movement trying to be improved) will be

compared to those adaptations that take place with task training alone.

Particularly, I will describe a new exercise (the FHS) which has been designed to

allow subjects to move with similar movement patterns to the acceleration phase

of a sprint run. This series of studies will also help determine whether adaptations

to resistance training are specific to movement pattern and velocity when it is

performed concurrently with task practice. They will similarly provide an insight

into the neuromuscular adaptations to concurrent resistance- and task training.

Past research has speculated, rather than defined, adaptations to such training

(e.g. Delecluse et al., 1995). Importantly, well-trained subjects will be used as

subjects in this study so that the results are more applicable to competitive

athletes. Therefore the results will assist coaches design training programs to

enhance athletic performance.

7

1.4 OVERVIEW OF STUDIES

1.4.1 STUDY ONE

Tasks such as the VJ, BJ and sprint run are commonly performed in many sports,

as well as in studies investigating human performance. Given that adaptations to

RT are specific to the movement patterns of training exercises (Abernethy et al.,

1994; Rutherford et al., 1986; Wilson et al., 1996) it might be important that

training exercises aiming to improve these tasks, and tests designed to assess

performance, have similar movement patterns to the tasks. As there is limited

data comparing common resistance and task exercises, the main purpose of the

first study was to describe and compare the movement patterns of athletic

subjects performing VJ, BJ, SQ and jump-squat (JSQ) tasks. A second purpose

was to compare the movement patterns of a unique exercise, named the forward

hack squat (FHS; see Figure 3.1), and the acceleration phase of a sprint run. The

FHS exercise was designed to allow subjects to train with a movement pattern

similar to the acceleration phase of a sprint run. Due to space limitations in the

biomechanics laboratory at Southern Cross University the sprint run could not be

properly analysed and the kinematics of the FHS were compared to sprint running

data published by Jacobs and Ingen Schenau (1992).

1.4.2 STUDY TWO

Given the results of Study One, the FHS and SQ exercises were chosen for use in

training and testing in this thesis. However, performing 1-RM tests for the

purposes of assessing performance or designating training loads can be a long

process. It would therefore be ideal to use simpler isometric tests for these

purposes. The aim of this study was first to examine the reliability of isometric

squat (ISQ) and isometric forward hack squat (IFHS) tests to determine if

repeated measures on the same subjects yielded reliable results, and second to

8

examine the relationship between isometric and dynamic measures of strength

to assess validity.

1.4.3 STUDY THREE

Given the FHS is a new exercise and will be used to assess performance changes

with training it was important to establish its test-retest reliability. The purpose of

this study was to examine the reliability of complex, dynamic unilateral and

bilateral FHS tests and determine whether the loads lifted during the tests affected

their reliability.

1.4.4 STUDY FOUR

While Study One aimed to show which resistance- and performance tasks were

similar in their kinematics, it was still unclear if subjects who performed well in a

resistance task also performed well in its associated performance task. In order to

more clearly determine which resistance and task movements were most similar

in their movement characteristics the relationship between subjects’ performances

in the squat lift, FHS, vertical jump (VJ) and 20 m sprint tests was determined. It

was hypothesised that subjects should perform equally well in tests where the

movements were similar.

1.4.5 STUDY FIVE

The results of studies one and four provided information regarding the kinematics

of, and performance relationships between, the squat, FHS, VJ and 20 m sprint.

From this, it was evident that subjects exhibited similar movement patterns during

the FHS and sprint tests. Furthermore, relative to other subjects in the studies,

subjects who performed well in the FHS also performed well in the sprint run.

Similar movement patterns were also shown for the VJ and jump squat (JSQ)

9

exercises. While a slightly better performance relationship was seen between

the ISQ and VJ, subjects who performed well in the VJ tests seemed also to

perform well in the SQ tests. Given the information from the two studies, it was

hypothesised that if adaptations to RT were specific to the movements used in

training greater performance benefits would possibly be seen in the sprint after

FHS training while greater improvements in the VJ might be seen after squat (or

JSQ) training.

Since most athletes perform RT concurrently with task training, a longitudinal,

concurrent training study (Study Three) was undertaken. The first purpose this

study was to determine whether changes in VJ, sprint run and strength tests were

related to the movement patterns of multi-joint, dynamic RT in well-trained

subjects. The second purpose was to compare neuromuscular and performance

changes when the VJ and sprint training (i.e. task practice) was performed by

itself or concurrently with RT.

10

1.5 LIMITATIONS

While the conclusion was made from Study One (Chapter 3) that the movement

patterns of the forward hack squat (FHS; see Figure 3.1) and acceleration phase

of sprint running were similar, no statistical comparisons were made because raw

data describing the kinematics of the sprint start were not available (i.e. data from

the FHS were compared to figures presented for the sprint start by Jacobs &

Ingen Schenau, 1992).

The student population of Southern Cross University is small (approx. 7000) so

subject recruitment can be difficult, especially for studies such as those in this

thesis where well-trained subjects were used.

Only a small number of subjects (N = 23) completed Study Five (Chapter 7). This

was due to the small subject number recruited for the study due to the small pool

from which to draw subjects, the necessity to recruit well-trained subjects and also

to drop out from unforseen circumstances. Not only would this reduce the

likelihood of statistically significant findings but increase the risk of type I error.

Subjects in Study Five only trained for 5 weeks (after familiarisation). Therefore,

long-term adaptations to such training are difficult to estimate. A longer training

period was not possible given a long holiday period between semesters. This

would have made monitoring subject training unreasonably difficult.

While subjects in Study Three were asked to ‘continue their normal training while

ceasing any RT that was not part of the study’, this was difficult to monitor.

Therefore, training performed outside this research may have influenced the

results.

Changes in the nervous system after training in Study Five were investigated

using surface electromyography. While cross-talk would have been minimal given

11

the large muscles over which electrodes were placed (approximate pick-up

area � 20 mm; Barkhaus & Nandedkar, 1994; Fuglevand et al., 1992; Lynn et al.,

1978). There are inherent limitations to surface electromyography in dynamic

contractions (e.g. changes in muscle length affect EMG wave forms; Okada,

1987) and there is diffuculty in determining longitudinal changes in muscle

recruitment.

1.6 DELIMITATIONS

While the subjects used in Study Five were classed as ‘well-trained’, their training

histories were not similar. Training programs for different sports differ to suit the

characteristics of the sport. A four-week familiarisation phase was included to

ensure some of the training performed by the subjects in the lead up to the

training study (Study Five) was similar. However, it is difficult to classify these

subjects and delimit the results of this thesis. Nonetheless, it can be assumed

that the results can only be directed at healthy, athletic men and women of the

age range 18 – 35 years.

While the concurrent training regimes used in Study Three were designed to

assess the effects of concurrent resistance and speed training on physical

performance, many athletes perform different regimes. The number and intensity

of resistance- and task training sessions performed by athletes varies

independently. The results of the present thesis provide some insight as to what

adaptations could occur with concurrent training regimes, but it is unclear what

adaptations occur to other regimes.

12

CCHHAAPPTTEERR 22:: LLIITTEERRAATTUURREE

RREEVVIIEEWW

13

2.1 INTRODUCTION

The literature relating to movement pattern- and velocity-specific performance

adaptations to resistance, sprint and concurrent training, the neuromuscular

adaptations to such training, and the neuromuscular principles that govern human

movement (i.e. force-velocity and torque-angle relationships, energy kinetics of

muscular contraction, principles of stretch-shorten movements, coordination of

complex movements, etc.) is vast. The purpose of the present literature review is

not to discuss all aspects of neuromuscular and musculoskeletal function but to

provide a synopsis of research into the movement pattern- and velocity-specific

adaptations to training, and the possible positive and negative effects of

resistance training per se. This will further highlight the necessity of the present

research.

Each of the three separate studies described in this thesis has its own introduction

in which important concepts and scientific findings that are relevant to that

particular area of study are presented. In this literature review, research

examining movement-pattern specific adaptations to resistance training will be

presented with some discussion as to the mechanisms that might cause such

changes. Further, literature documenting velocity-specific performance

improvements from resistance training (RT) and the mechanisms responsible for

this specificity will be reviewed. Finally, a short discussion of the possible positive

and negative effects of resistance training on movement performance will be

presented. It will highlight many of the dilemmas faced by athletes and coaches

trying to determine the optimum combination of resistance- and task training in a

concurrent training regime.

14

2.2 EFFECT OF RESISTANCE TRAINING MOVEMENT PATTERN ON

TASK PERFORMANCE

Research investigating the movement pattern-specific adaptations to RT has

focussed on several factors, including: 1) body position, 2) muscle lengths and

joint angles, 3) unilateral and bilateral specificity, 4) type of contractions, and 5)

type of pre-contractions. All of these factors have been shown to influence

strength adaptations and may affect both the movement pattern- and velocity-

related changes that occur with RT.

2.2.1 Body position

Body position refers to the orientation of the body relative to a reference plane and

is often described by terms such as supine, prone, standing, seated, lying,

recumbent, curled and flat. In one of the first studies of the influence of body

position on strength adaptations, Raasch and Morehouse (1957) trained subjects

with an elbow flexion exercise while in the standing position. When tested in both

the standing and supine positions, strength increases were significantly greater

when subjects were in the familiar, standing position. Later, Solomonow et al.

(1986), studying the activity patterns of the elbow flexor and extensor muscle

groups, reported a change in antagonist activity between different body positions

that may have been a compensation for the change in body orientation relative to

gravity. Thus, the findings of Raasch and Morehouse (1957) were supported by

this work.

More recently, Abernethy and Jürimäe (1996) reported differences in subjects’

triceps strength when testing was performed using a triceps test similar to that

used in training and an unfamiliar test. After performing standing triceps

pushdown, close-grip bench press and triceps kickback exercises, the rate of

change in standing triceps pushdown strength differed to strength in the unfamiliar

supine triceps extension exercise. Furthermore, the result of a factor analysis

15

indicated that strength in these tasks were associated with different factors in

three of four testing occasions over the 12 weeks of training. Thus the body

position adopted during training may have influenced strength adaptations.

Wilson et al. (1996) found that subjects who performed bench press training

improved significantly in a bench press throw (8.4%) but not in a push-up test

(0.7%). The push-up test was performed at a similar movement velocity and with

similar kinematics, but in an inverted position (i.e. the force was directed

downward rather than upward). It is therefore likely that body position was the

factor that most notably affected the adaptation to training. Thus, research

investigating strength and performance improvements after a period of weight

training has shown strength improved most notably in exercises where the body

position adopted was similar to that of the training exercise. Strength gained by

training in one body position may therefore not completely transfer to strength

improvements in another (Raasch & Morehouse, 1957; Wilson et al., 1996).

2.2.1.1 Mechanisms responsible for body position-specific performance

changes

The mechanisms responsible for the body position-specific training response have

not been extensively researched. However, it is possible that different postures

are associated with different muscle or motor unit recruitment strategies.

Solomonow et al. (1986) found differences in antagonist activity between elbow

flexor and extensor muscle groups with different body orientations. Such changes

were hypothesised to compensate for differences in the influence of gravity

between the body positions. Person (1974) reported changes in the recruitment

order of rectus femoris motor units as the posture of a task was changed from a

‘fixed’ to a ‘free’ condition. A difference in the direction of force application that

occurred in response to the change in posture may have contributed to this

change in neural drive. Also, muscles with similar actions show different levels of

activation (Mao et al., 1996) and the frequency content of their myoelectric signals

change (Signorile et al., 1994) depending on the task performed. Motor units of

16

the same muscle have also been shown to be recruited differently depending

on the direction of force application (Ter Haar Romeny et al. 1982, 1984). These

findings suggest that the nervous system used different strategies to activate

muscles when the body position was changed. It is likely that adaptations in the

nervous system to resistance training depend on the body positions adopted.

However these neural adaptations are not well understood.

No research has investigated muscle architectural adaptations (i.e. orientation of

fibres, length of fibres, etc.) to training in different body positions. The effects of

gravity would be different in different body positions that would alter the force

magnitude and direction requirements of a muscle. The magnitude and direction

of forces produced by muscles are influenced by their architecture, particularly in

pennate muscles; indeed many different types of pennate muscles exist and each

has different force generating properties. Changes in the angle of the

aponeurosis (the extension of the tendon that passes through the muscle and

onto which fibres attach) relative to the tendon, angle of fibres to the aponeurosis,

and heterogeneity of within-muscle fibre arrangements might have some effect on

the magnitude and direction of force production. Research examining changes in

architecture after training is required before the relationship between architecture

and body position-specific strength changes can be described.

2.2.2 Joint angles and muscle lengths

Many researchers have examined the training-induced increase in force at one

joint angle or muscle length to force produced at another joint angle or muscle

length (Kitai & Sale, 1989; Lindh, 1979; Weir et al., 1994). Most of the research

has referred to the effects of manipulating the joint angle, rather than muscle

length per se, on strength adaptations during resistance training. Changes in the

length of muscles crossing a joint do not directly accompany changes in joint

angle since the moment arm of the muscle-tendon unit often varies as the joint

angle changes (Nemeth & Ohlsen, 1987; Visser et al., 1990). Nonetheless, for

single-joint tasks at least, the length of the muscle-tendon unit is usually

17

determined by the joint angle. For example, if contraction conditions were held

constant (i.e. force, duration, muscle fatigue, etc.), the muscle-tendon length

would not change between repeated contractions at a particular joint angle. For

the purpose of this literature review therefore, the term ‘joint angle’ will describe

the angle between bones comprising a joint and the corresponding length of the

muscles crossing that joint. Given that most research (e.g. Lindh, 1979; Weir et

al., 1994, 1995a,b) specifically uses only single-joint movement tasks, muscle

length and joint angle will be considered synonymous.

2.2.2.1 Joint angle specificity in isometric contractions

Much research suggests that isometric strength is likely to increase most at and

around the joint angles which strength training is performed (Gardner, 1963;

Belka, 1968; Kitai & Sale, 1989; Lindh, 1979; Weir et al., 1994, 1995b). Early

research by Gardner (1963) showed that significant increases in isometric knee

extensor torque were only seen at the angle at which training occurred. Also,

Lindh (1979) found that isometric strength increased by approximately 30% at the

angle at which training was performed but only 12% at the non-training angle

(angles differed by 45o). Other evidence suggests that there might be a greater

movement pattern-specific effect when training is performed at shorter muscle

lengths (Thepau-Mathieu et al., 1988). Nonetheless, there appears to be angle-

specific performance changes with training.

As yet, few studies have shown non-specific adaptations to resistance exercise.

Much of the research that has not shown clear angle-specific effects required the

subjects training at larger joint angles (and consequently long muscle lengths

[Bandy & Hanten, 1993; Meyers, 1967]). Nonetheless, strength changes have

been shown to be more general when training is performed at such angles

(Thépaut-Mathieu et al., 1988). In all, strength gains are greater for movements

performed at or near the training angle than at very different joint angles when

resistance training is performed in isolation (i.e. not concurrently with other task

training).

18

2.2.2.2 Joint angle specificity in dynamic movements

Much of the research on angle-specific training adaptations has utilised isometric

training to elicit strength gains, so questions could be raised as to the validity of

these results to dynamic training (Wilson & Murphy, 1996). Although the research

on joint angle specificity of dynamic training is sparse, and the specificity of

dynamic training is not conclusive, the same angle-specific adaptations have been

shown after dynamic forms of training. Graves et al. (1989) had one group of

subjects train the knee extensors through a range of motion from 120 - 60o of

flexion, while a second group trained from 60 - 0o of flexion. After the training

period the first group performed significantly better in isometric strength tests

between the angles of 120 and 60o, while the second group performed

significantly better at angles between 60 and 0o of flexion. This suggested that

strength changes after dynamic training were also specific to the joint range of

motion despite the testing and training modes being different (dynamic versus

isometric). The angle-specific training effect however should be examined by

studies utilising dynamic, as opposed to isometric, training and testing modes.

2.2.2.3 Mechanisms underlying the angle-specific effect

Changes within the Central Nervous System – Whole muscle activation and inter-

muscular coordination

No single mechanism has been proven responsible for the angle-specific

adaptations to resistance training, although adaptations within the central nervous

system (CNS) have been implicated. Kitai & Sale (1989) found that voluntary

isometric plantar flexor strength increased only at or near the training angle while

evoked twitch force did not improve at any angle. Thus, joint angle specificity was

only observed during the voluntary contractions. Furthermore, since twitch force

19

did not improve it is likely that the angle-specific strength changes were a result

of changes in neural drive to the agonist muscles. Alternatively, the lack of

strength increases during the twitch condition might suggest that the muscle was

not maximally activated by this method.

Further, results of studies investigating cross-education (a performance

enhancement of a non-training limb after unilateral training) have shown strength

increases in an untrained limb that were similar to the trained limb (Weir et al.,

1994). Such research suggests that changes in hypertrophy and muscle

architecture could not have influenced the torque-angle relationship since there

was no stimulus for such changes. Evidence however that myosin light chain

changes can occur in a ‘control’ limb (Srihari et al., 1981) suggests that such

speculation might not be warranted. Furthermore, cross-education is not always

seen, even after similar training regimes are performed (Weir et al., 1994 versus

1995b).

Some researchers also speculate that changes in co-contraction patterns could be

responsible (Weir et al., 1994). Both increases (Baratta et al., 1988) and

decreases (Carolan & Cafarelli, 1992; Pousson et al., 1999) in muscle co-

contraction have been reported after periods of resistance training. However no

studies have shown that a change in co-contraction patterns occurred

simultaneously with angle-specific strength changes. It is unlikely that changes in

the recruitment of agonist muscles are responsible for angle-specific performance

changes. Much research has shown that changes in muscle recruitment are rare

with resistance training (Brown et al., 1990; Carolan & Cafarelli, 1992; Harridge et

al., 1999, Young et al., 1985). Also, no changes in surface EMG have been

shown after angle-specific training (Weir et al., 1994; 1995b), but angle-specific

strength changes have been found after training involving electrical stimulation of

relaxed muscle (Martin et al., 1994). Thus, despite attempts to attribute angle-

specific changes to a neural origin, no studies have shown a direct link between

changes in muscle recruitment and angle-specific strength.

20

Changes within the Central Nervous System – Changes in intra-muscular

recruitment

Specially grouped motor units may also be involved in movement-specific strength

adaptations. Motor units in many upper body muscles are grouped as sub-

populations or ‘functional compartments’ based on the likelihood of their activation

during a given contraction (Ter Haar Romeny et al., 1982; 1984; Theeuwen et al.,

1994; Tonndorf & Hannam, 1994; Van Zuylen et al., 1988). Little research has

described compartmentalisation of lower limb muscles although fibres of the

gracilis (Schwarzacher, 1959), sartorius (Barrett, 1962; Schwarzacher, 1959) and

the semitendinosus (Barrett, 1962) have been shown not to run the entire muscle

length. This suggests that a similar ‘compartment-based’ organisation to upper

body muscles may be present in lower body muscles in humans.

While the functional significance of compartments has not been studied

extensively in humans, there has been considerable research on animal muscles

(Chanaud et al., 1991; Pratt et al., 1991). Chanaud et al. (1991) showed that the

cat biceps femoris and tensor fasciae latae were comprised of functional

compartments with differential synaptic inputs. Also, Loeb et al. (1987) measured

the EMG evoked by stimulation of the branches of the motor axon to the cat

sartorius muscle and found that each compartment was selectively activated.

Together, these two studies suggest that compartmentalised muscles may in fact

be comprised of small, uniquely-activated musclets. Zuurbier and Huijing (1993)

then discovered that fibres located in different regions of the rat gastrocnemius

medialis reached their optimum (length at which maximum contractile force is

produced) and slack (length at which no passive/elastic force is produced) lengths

at different overall muscle lengths. This suggested that innervation of

compartments may be dependent on fibre lengths, or at least the lengths of

sarcomeres constituting the fibres. Indeed, Van Zuylen et al. (1988) also found

that the recruitment of compartments within the human biceps brachii was

dependent on the joint angle, and therefore the muscle length, at which the

contraction was performed.

21

While not shown experimentally, it is possible that movements that are performed

through different joint angles are associated with different activation patterns of

compartmentalised muscles in a manner related to the length of sarcomeres. One

might expect therefore that a period of muscle length-specific (or joint angle-

specific) RT could promote rapid changes in the length of sarcomeres within

compartments, and possibly the number of sarcomeres within such

compartments. Such adaptations would alter the muscle length-specific (joint

angle-specific) force produced by these muscles.

Changes in the periphery - Sarcomere length/tension adaptation

The length at which sarcomeres produce optimum force varies with their resting

length (Ettema & Huijing, 1994; Gareis et al., 1992; Tabary et al., 1972) and

research has shown that changes in sarcomere length occur within days of

stimulus application (Herbert & Belnave, 1993; Williams, 1990). Furthermore, the

passive length-tension relationship is also altered after sarcomeric changes occur

(Goldspink, 1974; Tabary et al., 1972; Williams et al., 1990). Thus changes in

sarcomere length would influence the length-tension properties of a muscle.

Force stimuli (in the form of electrical stimulation) has been shown to promote

sarcomere changes (Williams et al., 1986). Williams (1990) also showed that only

acute periods of stretch (0.5 hours per day) were necessary to increase the

number of sarcomeres by up to 10% within two hours of the stretch. Lynn and

Morgan (1994) reported that decline running produced more sarcomeres in the rat

vastus intermedius fibres than incline running. Such results suggest that a stretch

(or perhaps force) stimulus need only be applied for short periods for adaptations

to occur.

It has not been confirmed however whether the length of sarcomeres adapts to

the muscle lengths at which resistance training is performed. Nonetheless,

Herring et al. (1984) showed that optimum sarcomere length could adjust to that

22

length where maximum muscle forces are required. Further, data of Weijs and

van der Wielen-Drent (1982, 1983) that was re-analysed by Herring et al. (1984)

predicted that sarcomere length was related most to either the muscle length

halfway between the greatest and least stretched position, or to the position where

maximum force was applied. It is therefore likely that the resting length of

sarcomeres adapts to force stimuli such that the length-tension relationship of its

constituent fibre is optimum when the greatest force is required. Given that

changes in sarcomere length occur rapidly, and well within the time frame of

angle-specific torque changes, such adaptations may be a factor in the angle-

specific response to training.

Changes in the periphery – Muscle pennation

Changes in the angulation of fibres relative to the aponeurosis or tendon

(pennation) could also affect the length-tension characteristics of a muscle.

Certainly muscles with greater pennation have a smaller length over which high

muscle forces can be produced (Kaufman et al., 1989; Wottiez et al., 1983). It is

unclear if this is due to increased pennation or the shortness of fibres associated

with these muscles. However the length at which optimum force is produced

would also be affected by the angle of pennation. Fibres of pennate muscles not

only shorten, but rotate, during muscle shortening (Benninghoff & Rollhauser,

1952; Muhl, 1982). As the angle between the fibres and tendon increases, the

amount of fibre-generated force being directed along the tendon decreases since

the fibres are pulling across rather than in line with the tendon. If fibres produced

the same tension at all lengths, the force generated by a muscle would be related

to the angulation of the fibres, i.e. maximum muscle force would be produced at

the longest muscle lengths. Since muscle fibres have an optimum length for force

development, the muscle length at which optimum force is produced in pennate

muscles would be related to both the fibres’ optimum lengths and the degree of

muscle pennation.

23

2.2.2.4 Summary

Strength changes with resistance training are specific to the joint angles (or

muscle lengths) at which training is performed. This appears true for both

isometric and dynamic movements. The mechanisms by which these changes

occur are not well understood. It is unclear whether sarcomere length changes

occur after a period of joint angle-specific training, whether certain regions within a

muscle are more or less active after training at specific angles, or whether there is

a change in the co-contraction of antagonist muscles after such training. While the

degree of fibre pennation might also affect joint angle-specific strength changes, it

is unlikely that factors such as hypertrophy or changes in the structure or

functioning of the joint itself are important.

2.2.3 Unilateral versus bilateral specificity

The effects of training either uni- or bilaterally have been described by two,

possibly related, phenomena. First, cross education describes an increase in

strength of an untrained limb when the contralateral limb is trained (Cabric &

Appell, 1987; Cabric et al., 1988; Laughman et al., 1983). Second, bilateral deficit

[or facilitation] refers to an effect whereby the maximum force that a muscle can

exert decreases [or increases] when the homologous muscle in the opposite limb

is contracted (Enoka, 1997). Athletes who often perform unilateral tasks (e.g.

cyclists) as well as untrained individuals have been shown to exhibit bilateral

deficit while weightlifters exhibit bilateral facilitation (Howard & Enoka, 1991).

Nonetheless, the bilateral deficit can be reduced (or perhaps reversed) by bilateral

training (Häkkinen et al., 1996; Rube & Secher, 1990; Tanaguchi, 1997) and a

bilateral facilitation can be reduced by unilateral training (Häkkinen et al., 1996;

Tanaguchi, 1997; Weir et al., 1997). These specific changes appear similar for

different exercise tasks (hand grip strength, leg extensor power and arm extensor

power [Tanaguchi, 1997]). However, the bilateral deficit is often greater for high-

speed movements (25-45%; Koh et al., 1993; Vandervoort et al., 1984) than

slower movements (<20%; Howard & Enoka, 1991; Koh et al., 1993). Therefore

24

specificity of training adaptations with respect to laterality exists (i.e. unilateral

versus bilateral training). The phenomenon has particular implications for the

training of athletes since many athletic pursuits are performed with the movement

of one limb (e.g. javelin, long or high jumping, kicking, etc.) or with alternating

limbs (e.g. swimming, running, cycling, etc.).

2.2.3.1 Mechanisms responsible for the bilateral deficit (facilitation)

Some investigations have shown decreases (Howard & Enoka, 1991; Koh et al.,

1993; Ohtsuki, 1983; Vandervoort et al., 1984) and others no change (Häkkinen et

al., 1995; Jakobi & Cafarelli, 1998; Schantz et al., 1989) in surface EMG (used as

a measure of muscle activation) with the force deficit that often accompanies

bilateral movements. The results of twitch interpolation studies are also equivocal

with different muscles showing different degrees of activation depending on

whether the movement was performed uni- or bilaterally (Herbert & Gandevia,

1996). Also Jakobi and Cafarelli (1998) found a large, but not statistically

significant, increase in muscle activation in unilateral movements.

The rate of force development (Koh et al., 1993) and mean power frequencies

(Oda & Moritani, 1994) of muscles activated under bilateral conditions is also less

than when activated unilaterally. This suggests perhaps that neural drive is

diminished in the bilateral condition. Such findings are consistent with decreases

in the H-reflex (i.e. the motoneuron pool is less excitable and associated motor

units less likely to fire) of a non-contracting limb that have been observed when

the contralateral limb is performing a movement (Kawakami et al., 1998).

Research so far suggests it is most likely that a decrease in neural drive is the

cause of force decrements in bilateral contractions.

It is unclear whether other neural changes are responsible. Ohtsuki (1983)

showed greater elbow flexor/extensor co-contraction during bilateral than

unilateral elbow flexion movements, although Koh et al. (1993) observed a

decrease in quadriceps/hamstrings co-contraction during bilateral leg extension.

25

It is unlikely however that increased concentration demands could affect force

produced during bilateral contractions as no bilateral deficit is seen when non-

homologous muscles or muscle groups are contracted (Howard & Enoka, 1991;

Ohtsuki, 1983; Schantz et al., 1989). Thus while some modifications of neural

drive probably occurs between uni- and bilateral movements, the mechanisms

responsible for the bilateral deficit are unclear. It does however seem that specific

adaptation and performance changes occur with uni- and bilateral changes.

2.2.4 Type of contraction

Adaptations to strength training appear to be specific to the type of contraction (ie

concentric or eccentric) performed in training (Hortobágyi et al., 1996, 2000;

Lacerte et al., 1992; Smith & Rutherford, 1995; Tomberlin et al., 1991). Generally,

eccentric training leads to better improvements in eccentric strength than

concentric training. The opposite is true for concentric training. It is unclear

whether eccentric or concentric training improves isometric strength the most with

some studies showing greater increases with concentric (Hortobágyi et al., 1996,

2000) but others eccentric (Smith & Rutherford, 1995) training. Therefore, while

some studies provide evidence that adaptations to training may not depend on the

type of contraction (Petersen et al., 1991; Singh & Karpovich, 1976), it is

anticipated that strength gains resulting from resistance training are specific to the

type of contraction performed. Unfortunately, only a few studies have investigated

the adaptations to eccentric and concentric isotonic/isoinertial training (Johnson,

1972; Johnson et al., 1976; Komi & Buskirk, 1972). The results of these studies

suggest that specificity of contraction type may be similar to that associated with

isokinetic training.

The influence of type of contraction will not be investigated in the present thesis.

However, given the specificity of adaptations to movement type, it will be held

constant between training groups in the training study that will investigate the

effect of movement pattern specificity of resistance training on task performance

(Study Five). Thus, an extensive review of literature will not be presented here.

26

2.2.5 Type of pre-contraction

Many sporting tasks require concentric muscle action subsequent to eccentric

contraction of the muscle. Examples of such tasks include running, jumping,

throwing and bounding/hopping. It is clear that vertical jump height, for instance,

is increased when subjects are allowed an eccentric contraction

(countermovement) prior to the concentric phase of a jump (Häkkinen & Komi,

1985; Häkkinen et al., 1987; Voigt et al., 1995). Similar results have been shown

for upper body tasks such as the bench press (Wilson et al., 1991). Increases in

performance have been largely attributed to increases in the impulse produced

during the early (first 370 ms; Wilson et al., 1991) part of the concentric phase.

Therefore, muscle actions that are preceded by an eccentric contraction are

associated with improved dynamic performance.

This improved performance is mostly attributed to the stretch-shorten cycle (SSC)

phenomenon. It has been commonly suggested that when a load is placed on a

muscle, its elastic (compliant) elements are able to store energy after being

stretched; this energy is released when the muscle contracts concentrically. The

use of elastic energy during the concentric phase of a movement is believed to

augment power output and/or movement efficiency (Komi, 1984; Miller et al.,

1981; Norman & Komi, 1979). However, greater performances in tasks that are

preceded by an eccentric contraction may also be explained by the fact that the

muscles are more active after the eccentric phase. Bobbert et al. (1996) studied

the difference between vertical jumps with and without a countermovement (i.e. a

downward phase prior to the upward, propulsive phase) using modelling

techniques. Their results suggested that the countermovement allowed muscles

to achieve a ‘high level of active state’, attachment of cross-bridges, and force

before shortening. Muscles were therefore able to produce more force (perform

more work) earlier in the propulsive phase. Similar findings were also reported by

Walshe et al. (1997).

27

Motor unit recruitment may also vary when the pre-contractions used in training

exercises are changed. While smaller slow-twitch motor units are often activated

prior to larger fast-twitch motor units (Milner-Brown et al., 1973), Nardone et al.

(1989) demonstrated that a large proportion of high-threshold, fast-twitch motor

units were active during lengthening contractions. Therefore, fast-twitch motor

units that are not often activated during brief concentric contractions might be

better activated by a prior eccentric contraction.

Since movements utilising an eccentric component are functionally dissimilar to

those that do not, it may be important that training exercises for tasks that involve

prominent eccentric phases replicate the task pattern precisely. The influence of

type of pre-contraction will not be investigated in this thesis. It will however be

held constant between training groups in the training study that will investigate the

effect of movement pattern specificity of resistance training on task performance

(Study Three). Thus, a comprehensive review of literature will not be presented

here.

2.2.6 Summary

Adaptations to resistance training appear to be specific to the movement patterns

of the training exercises. It may be important therefore that training exercises

aiming to improve athletic performance be similar in their body position, laterality

and the joint angles through which the movement is performed. It would also be

important to replicate the contractions and pre-contractions. Most research

suggests that movement pattern adaptations are largely of neural origin.

However, some evidence suggests that adaptations at the sarcomere level may

be a factor. Research has not provided evidence in favour of any one

explanation.

28

2.3 EFFECT OF RESISTANCE TRAINING MOVEMENT VELOCITY ON

TASK PERFORMANCE

Physiological adaptations to training have been shown to be specific to the

velocity of training. Much of the research that has examined the velocity-specific

training effect have used isokinetic training and testing procedures with relatively

little research using free-weight, isotonic resistance training techniques. Since

adaptations to these two training modes may not be similar, the literature

reviewed in this section will be addressed with respect to training mode.

2.3.1 Isokinetic, velocity-specific training studies

While peak torque is often measured in isokinetic studies, the testing protocol

used by researchers such as Perrine and Edgerton (1978) and Caiozzo et al.

(1981) involved graded knee extensions. This was to ensure maximum force

production (torque maximum) occurred at a specific angle (30o of knee flexion) to

control oscillations in the dynamometer and limit fatigue during the initial stages of

the contraction. Small performance differences between ‘peak torque’ and ‘angle-

specific torque’ methods are possibly due to differences in testing protocol or

strength levels of athletes (Hortobágyi & Katch, 1990). However, comparisons

between ‘angle-specific’ and ‘peak torque’ methods are presented in Bell and

Wenger (1992) and Kannus et al. (1991) and show minimal differences between

the torque curves determined both ways. Therefore, for the purpose of this

review, the results from studies which have used ‘angle-specific’ and ‘peak torque’

methods will be considered together.

Velocity-specific training adaptations have been shown in numerous studies.

Moffroid and Whipple (1970) trained subjects on a knee extension exercise at

either 36o.s-1 or 108o.s-1 and tested at a range of velocities from 18 to 108o.s-1. All

subjects primarily increased torque at and below the training velocity with subjects

who trained at 108o.s-1 increasing their torque production at a greater range of

29

movement speeds. Similar results have been reported by a number of other

researchers (Costill et al. 1979; Coyle et al., 1981; Ewing et al., 1990; Lesmes,

1978; Petersen et al., 1989). Some studies have also shown torque and power

increases at slower speeds but also higher speeds after slow isokinetic training

(Caiozzo et al., 1981; Colliander & Tesch, 1990; Kanehisa & Miyashita, 1983;

Petersen, 1988). Thus, while there is substantial evidence suggesting that

strength, as measured by joint torque or power, increases most at the velocity at

which the subjects trained there may be some carryover to other velocities.

Interestingly, while few studies have shown an effect of periodised training,

Doherty and Campagna (1993) showed that periodised slow to fast velocity

training culminated in greater mean isokinetic torque at 180o.s-1 than a ‘slow’

training group and a ‘fast’ group who trained at that speed. Thus adaptations to

periodised training may be different to those of non-periodised training.

Despite the number of studies that report a significant velocity-specific training

effect after isokinetic training, some studies show contrasting results (Bell &

Wenger, 1992; Bell et al., 1989; Housh & Housh, 1993; Jenkins et al., 1984;

Lacerte et al., 1992). For example, Bell et al. (1989) showed that increases in

peak knee extensor torque were lowest at slow speeds and greatest at higher

speeds despite training being performed at an intermediate speed. Also, Housh

and Housh (1993) reported elbow and knee flexion/extension torque increases at

fast and slow speeds after training at intermediate speeds (120o.s-1). It has been

suggested therefore that training performed at intermediate velocities (100o.s-1 –

200o.s-1) may be associated with less-specific adaptation (Bell & Wenger, 1992)

although some researchers have reported velocity-specific adaptations even at

these velocities (Petersen et al., 1984). Therefore, despite some inconsistency,

the weight of evidence supports a velocity-specific adaptation to isokinetic

exercise. It is not clear why differential results have appeared, the unreliability of

isokinetic tests (Steiner et al., 1993), training status of subjects and the length of

training studies might be a factor.

30

2.3.2 Isokinetic training effects on task performance

Few researchers have investigated the transfer of strength gains made with

isokinetic training to performance improvements in isotonic/isoinertial tasks.

Smith and Melton (1981) showed that subjects who trained their knee extensors

and flexors at fast (180, 240 and 300o.s-1) speeds improved their vertical jump

(5%), broad jump (9%) and 40-yard sprint time (10%). Subjects who trained at

slow (30, 60 and 90o.s-1) speeds improved their vertical jump (4%), but did not

improve broad jump (0%) or 40-yard sprint time (-1%). This result suggests some

velocity-specific transfer occurs from isokinetic training to task performance.

However, Van Oteghen (1973) used a leg press exercise at two different velocities

to train volleyball players. After training, there was no difference in performance

of a jump test between the two groups although these groups performed better

than an untrained control group. Given that Smith and Melton (1981) found no

significant effect of training velocity on vertical jump also, it appears as though the

vertical jump is less affected by training velocity than broad jump and running

tasks. It is also unclear whether the lack of movement pattern similarity between

the tasks would have affected adaptations. Thus, while it is not conclusively

shown, it is possible that even high-velocity isokinetic training might improve

performance of complex high-speed tasks.

2.3.3 Free-weight, isotonic training studies

Research investigating the velocity-specific adaptations to free-weight, isotonic

training is also sparse. Increases in fast-speed dynamic performance has been

shown to be greater with high-speed (30% of 1RM) training and plyometric

training than slower resistance training (Wilson et al., 1993). There also seems to

be no effect of resistance training on the speed of an unloaded, complex

movement unless some training of the movement is performed (Voigt & Klausen,

1990). A similar result was found by Adams et al. (1992) who reported greater

(10.7 cm) improvements in vertical jump performance after combined squat and

31

plyometric training than squat (3.3 cm) or plyometric training (3.8 cm) alone.

Other studies failed to show a significant velocity-specific training effect with

resistance-type training. Palmieri (1987) found no significant differences in leg

power in a vertical jump between groups who performed squat lift training at slow,

fast, or periodised slow to fast movement speeds. Also, Young and Bilby (1993)

found no differences in strength or muscle size of subjects who performed either

slow or fast squat lifts despite a trend toward a greater rate of force development

in subjects who performed faster movements. Nonetheless, increases in strength

and power might occur easily regardless of training type in subjects with a limited

training history such as those in these two studies. Also, Pousson et al. (1999)

showed no changes in elbow flexor movement velocity of a group who performed

light-load (35% of 1 RM) training at their fastest possible speed. The difference in

training (isotonic) and testing (isokinetic/isometric) modes might explain the lack of

performance change (Duncan et al., 1989).

Unfortunately, studies that have investigated adaptations to high-velocity training

have used exercises performed at limb velocities below those achieved in many

sporting situations. For instance, the angular velocity at the hip during maximum

velocity running exceeds 500o.s-1 (Mann & Herman, 1985). It may be difficult to

consistently replicate, in a laboratory or gymnasium, speeds that are achieved in

the sporting situation; it is also unclear whether it is necessary to achieve these

speeds for beneficial adaptations to occur. Furthermore, isoinertial movements

are often characterised by a prolonged deceleration period toward the end of

concentric and eccentric phases. Such training is characterised by lower

movement velocities, lower muscle power and a reduced EMG of agonist muscles

compared to movements without a deceleration phase (e.g. bench throws;

Newton et al., 1997). Using this form of training may therefore not provide an

optimum training stimulus. Another factor that limits the use of data collected in

these studies is the length of training periods. Training studies are generally less

than three months in duration (e.g. Young & Bilby, 1993: 6 weeks). Therefore, the

effect of long-term high-velocity resistance training is still not clear. To understand

the influence of training velocity on task performance, the physiological

32

adaptations to resistance exercise must be considered.

2.3.4 Mechanisms contributing to velocity-specific strength changes

2.3.4.1 Neural Factors

Muscle Activation

Even during maximal voluntary contractions, individuals may not be able to fully

activate their muscles (Enoka & Fuglevand, 1993) or may not be able to fully

activate their muscles on each of a series of maximal contractions (Allen et al.,

1995). Much research has shown increases in surface EMG after both ‘traditional’

(Higbie et al., 1996; Narici et al., 1989; Ozmun et al., 1994) and explosive jump

training (Häkkinen & Komi, 1983, 1985, 1986; Häkkinen et al., 1985a,b) and

Häkkinen et al. (1987) showed increases in EMG accompanied increases in

power production of elite weightlifters during periods of higher-than-normal

training intensity. The increases in EMG were considered a strong indication of

increases in the level of total muscle activation. Other researchers however have

not shown increases in EMG after periods of resistance training (Cannon &

Cafarelli, 1987; Garfinkel & Cafarelli, 1992; Komi & Buskirk, 1972) or that only

‘explosive-type’ training has the propensity to increase muscle activation. Thus

there is some speculation that adaptations can occur without increases in EMG. It

is also possible that increases in EMG reflect increases in motor unit

synchronisation which is associated with higher EMG (Yao et al., 2000). It is

unclear whether there is a velocity-specific change in EMG after training.

The twitch interpolation technique first performed by Merton (1954) has been used

to examine levels of muscle activation. Most research has shown no change in

muscle activation after various forms of training using this technique (Brown et al.,

1990; Carolan & Cafarelli, 1992; Harridge et al., 1999; Herbert et al., 1998; Sale et

33

al., 1992). Supramaximal stimulation techniques have also shown no change

in stimulated force even after increases in voluntary force were seen (Davies &

Young, 1983; Davies et al., 1985; McDonagh et al., 1983; Young et al., 1985).

These results are possibly a result of muscle activation being nearly maximal in

most subjects (Carolan & Cafarelli, 1992; Garfinkel & Cafarelli, 1992). However

recent advances in the technique have shown that activation may often be

incomplete (Jakobi & Cafarelli, 1998; Kalmar & Cafarelli, 1999). A second reason

might be that the testing (isometric) and training (dynamic) modes were dissimilar

(Murphy & Wilson, 1996). It is therefore unclear whether voluntary muscle

activation assessed by muscle stimulation techniques is improved with training.

The measurement of transverse relaxation time (T2) of muscle by magnetic

resonance imaging has reportedly provided more accurate estimates of total

muscle activation (Fisher et al., 1990; Fleckenstein et al., 1993). Such research

has shown that, with few exceptions (e.g. Dowling & Cardone, 1994), maximal

muscle activation is uncommon (Adams et al., 1993; Allen et al., 1995). Akima

and colleagues (1999) also showed increases in muscle activation after just two

weeks of isokinetic training with no changes in muscle cross-sectional area or

fibre areas. However no research has compared changes in muscle activation in

subjects who have performed high- and low-velocity training.

While techniques that estimate muscle activation have a lot to offer in terms of our

understanding of neural adaptations to training, the results of such studies have

been inconclusive. Therefore other methods of assessing changes in the nervous

system have been employed. Evidence from such research has suggested that

increases in centrally-mediated muscle activation might not occur with resistance

exercise. Lyle and Rutherford (1998) reported similar increases in voluntary

strength of subjects trained by tetanic stimulation (involuntary) or under voluntary

conditions. Martin et al. (1994) has also shown increases in strength with training

involving electrical stimulation of relaxed muscle. Since neural commands are not

required for the muscular contraction in stimulated contractions it is unlikely that a

central adaptation could occur. Herbert et al. (1998) also showed that while

34

strength increased in weight training subjects, others who performed imagined

contractions did not improve. There were also no changes in muscle recruitment

as measured by twitch interpolation. Thus, rapid and significant increases in

strength have been shown after training where central nervous system changes

are unlikely. There is mounting evidence that increased muscle recruitment

mediated by the CNS does not occur with resistance training or is at least not the

only contributing factor to strength improvements.

‘Muscle activation’ describes both the number of active motor units and their

discharge rates (firing frequency). Evidence from research investigating

maximum discharge rates of motor units suggests motor units rarely receive

action potentials at a rate required for maximum activation to occur (Bellemare et

al., 1983; De Luca et al., 1982; Freund et al., 1975; Tanji & Kato, 1973).

However, those motor units with high-thresholds for recruitment (typically fast-

twitch) decline in their discharge rates rapidly after the motor unit becomes active

(De Luca et al., 1982; Grimby & Hannerz, 1977; Marsden et al., 1983). Thus it is

possible that motor units with high discharge rates are difficult to record and might

produce biased (lower) estimates of discharge rate (Enoka, 1997). Nonetheless,

high discharge rates among motor units occur infrequently. Increases in

discharge rates would thus be useful in allowing greater muscle forces to be

produced.

The trainability of motor unit discharge rate has not been conclusively determined.

Disuse of a muscle has been shown to reduce a subject’s ability to activate that

muscle (Duchateau & Hainaut, 1990; Yue et al., 1994). For example, Duchateau

& Hainaut (1990) immobilised subjects’ hands and wrists for 6-8 weeks.

Maximum recruitment thresholds for the muscles studied increased from

approximately 30% to 50% of MVC suggesting that motor units were not as

readily recruited. Few studies have investigated the effects of resistance training

on discharge rates. Patten et al. (1995) found an increase in the maximum

discharge rates for elderly subjects (36 to 46 Hz) but not for young subjects (47 to

46 Hz) in hand muscles. Leong et al. (1995) also showed that elderly subjects

35

could possibly increase their motor unit discharge rates by comparing

weightlifters and inactive subjects (mean age = 71 yrs). While there were no

differences in discharge rates during submaximal knee extensions discharge rates

were significantly higher for the weightlifters during maximal efforts (25 vs 20 Hz).

Thus, at least in elderly subjects, resistance training appears to cause an increase

in the discharge rates of motor units during maximal efforts. Again, it is unclear

whether such adaptations occur with high-velocity training although such an

adaptation could have benefits for high-speed force production.

Selective Activation of Muscles

Muscles that have the same or similar actions are often activated differently

depending on the constraints of a task (Buchanan & Lloyd, 1997; Nakazawa et al.,

1993; Nardone & Schieppati, 1988; Van Gröeningen & Erkelens, 1994). Studies

investigating muscle recruitment patterns during movements of different speeds

have shown that muscles with high fast-twitch fibre content are recruited mostly

when high forces or movement velocities are required (Duchateau et al., 1986;

Nardone & Schieppati, 1988). The selective recruitment of muscles with high fast-

twitch fibre contents might be an advantage in movements where shortening

velocities are fast. In extreme cases the recruitment of slower-contracting

muscles might retard muscle contraction. It is also likely that selective recruitment

of fast-contracting muscles would be particularly important in tasks involving rapid

alternating (concentric-eccentric) movements. Indeed the performance of

eccentric contractions, especially fast contractions, largely incorporates fast-twitch

fibres and muscles with high fast-twitch fibre content (Nardone & Schieppati,

1988). Evidence that such a phenomenon might be present has also been

presented by Moritani and coworkers (1990) who reported electromyographic

evidence of selective fatigue of the medial gastrocnemius as compared to the

soleus during prolonged (60 s) hopping. Whether high-speed training affects the

recruitment of muscles has yet to be determined.

36

Muscle activation strategies might not be wholly related to the muscles’

contraction properties. Almasbakk and Hoff (1996) found that groups who trained

with light or heavy bench press loads improved their movement velocities similarly

in bench press tests. The authors hypothesised that since the group who trained

with almost no load improved their performance similarly to a heavy training

group, velocity-specific adaptations were primarily a result of ‘learning’ or more

efficient inter-muscular coordination. However testing loads were also very light

(� 20 kg). It is also unclear if these training groups would have improved as much

as a group who trained at high velocities. Pousson et al. (1999) found that

subjects who performed fast contractions against a light load (35% 1 RM) had less

co-contraction between agonist (biceps brachii) and antagonist (triceps brachii)

muscle groups, although only at the highest (300o.s-1) test velocity. While such

changes were not consistent across speeds, the result suggests that some

change in agonist/antagonist co-activation might mediate velocity-specific torque

changes.

Selective Activation of Motor Units

Fast-twitch motor units contain fibres that have faster contraction and half-

relaxation times. It would therefore be advantageous to recruit these motor units

preferentially in, or at least at onset of, high-speed muscular contractions. Motor

units are most often recruited in accordance with the size principle of recruitment

(Desmedt, 1981; Henneman et al., 1964) which suggests that motor units are

recruited in order from those with small axon diameters to those with large

diameters (i.e. from slow- to fast-twitch). Such recruitment strategies have been

shown under isometric ramp (Milner-Brown et al., 1973), dynamic (Kato et al.,

1985) and ballistic (Desmedt & Godaux, 1977) conditions. Nonetheless, research

has shown early recruitment of fast-twitch fibres in fast isometric (Grimby &

Hannerz, 1968), twitch and rapid acceleration (Grimby & Hannerz, 1977) and

faster eccentric (Nardone et al., 1989) contractions. The central synaptic

mechanisms responsible for selective recruitment strategies is as yet unknown

(Burke, 1991; Nardone et al., 1989).

37

Motor Unit Synchronisation

Motor unit synchronisation refers to the coincident timing of impulses from motor

units (Milner-Brown et al., 1973). Milner-Brown et al. (1973) showed that

weightlifters exhibited greater synchronisation (measured by a surface EMG

technique) than control subjects. Furthermore, subjects who performed six weeks

of resistance training increased their synchrony. Thus motor unit synchronisation

has been regarded as an adaptation to resistance-type exercise. Semmler and

Nordstrom (1998) echoed such findings and Moritani et al. (1987) reported

increased synchronisation of biceps brachii motor units after just two weeks of

high-velocity strength training. Nonetheless, evoked stimulation studies have

shown that greater forces (Clamann & Schelhorn, 1988; Lind & Petrofsky, 1978;

Rack & Westbury, 1969) and smoother contractions (Clamann & Schelhorn, 1988)

were possible with asynchronous stimulation. Asychronous stimulation might be

beneficial in that the first motor units to become active could overcome the

slackness of series elastic components of nearby fibres and allow the shortening

of those fibres to more directly result in muscle shortening.

Also, the rate of force development is greater in voluntary than evoked

contractions; evoked contractions are characterised by greater motor unit

synchrony (Miller et al., 1981). Thus it has been suggested that asynchronous

motor unit recruitment might be advantageous for increasing the rate of force

development (Behm & Sale, 1993b). At least, greater synchrony seems not to be

associated with greater force development.

Nonetheless, Miller’s research (1981) also showed that agonist muscles exhibited

a pre-movement silence (a brief period of minimal activity of alpha motoneurons)

that could allow more motoneurons to come to a non-refractory state. Such a

response has been hypothesised to allow greater motor unit synchronisation

(Conrad et al., 1983; Moritani & Shibata, 1994). While pre-movement silence is

not consistently exhibited prior to maximal concentric contractions in all subjects,

greater pre-movement silence has been shown to be more consistent in elite

38

power athletes (Kawahats, 1983). Nonetheless, pre-movement silence has

also been suggested to improve stretch-shorten cycle use (Aoki et al., 1989;

Walter, 1988) and be a built-in command by the central movement generators to

allow a switch between contraction sequence programs. Thus silent periods are

not necessarily evidence of central adaptations to increase motor unit synchrony.

Recent research (Yue et al., 1995) however has shown limitations with the surface

EMG method for assessing motor unit synchronisation. Newer cross-correlogram

procedures however also show that motor unit synchronisation may be variable.

Certainly synchronisation is influenced by handedness (Schmied et al., 1994;

Semmler & Nordstrom, 1998) and learning (Schmied et al., 1993). Either way,

changes in motor unit synchronisation hint that changes in neural connectivity can

occur (Kirkwood & Seers, 1991). Future research needs to compare differences

in motor unit synchronisation after high- and low-velocity resistance training in

order to describe the effects of movement velocity on motor unit synchronisation.

2.3.4.2 Muscular Factors

Muscle architecture

Muscle architecture refers to the size of a muscle and to the length and angulation

(pennation) of its fibres. In addition to changes in muscle (or fibre) hypertrophy,

changes in fibre length and pennation can occur with training. Longer fibres have

been theoretically and experimentally shown to exhibit faster contraction velocities

(Burkholder et al., 1994; Sacks & Roy, 1982; Wickiewicz et al., 1984). Indeed

longer fibres have been found in well-trained sprinters than in long distance

runners (Abe et al., 1999) and lesser-trained sprinters (Kumagai et al., 2000).

Also, Van Eijden et al. (1997) found that jaw muscles that are predominant in jaw

closing where high forces are required possess shorter fibres than muscles for jaw

opening where lower forces are required. Animal studies have shown that

increases in fibre length occur by an increase in the number, but decrease in the

39

length, of sarcomeres within the fibre while the opposite is true for decreases in

fibre length (Goldspink et al., 1974; Heslinga et al., 1995; Tabary et al., 1972).

Moreover, these changes can take place within hours or days of a stimulus

(Williams et al., 1986; Williams, 1990). Stimuli in research studies has included

immobilisation in a shortened (Goldspink et al., 1974; Heslinga et al., 1995;

Tabary et al., 1972) or lengthened position (Goldspink et al., 1974; Heslinga et al.,

1995; Williams et al., 1986) and electrical stimulation (Williams et al., 1986). Thus

it appears that physical stimuli can induce changes in fibre length. Differences in

fibre length between athletic populations may therefore be a specific adaptation to

the work performed by the athletes.

Muscles that frequently contribute to movements requiring high force also often

have greater pennation than muscles that contribute to higher-velocity, low force

movements (Van Eijden et al., 1997). It is unclear how pennation changes with

training. Some researchers have shown increases in pennation after resistance

training (Blazevich & Giorgi, 2001; Blazevich et al., 1998; Kawakami et al., 1995)

while others have shown no change (Rutherford & Jones, 1992). It is also unclear

how increased pennation benefits high force development. Some researchers

suggest that greater pennation allows more contractile tissue to attach to a given

area of tendon (Kawakami et al., 1993; Rutherford & Jones, 1992). However,

while some studies support a relationship between muscle pennation and size

(Kawakami et al., 1993, 1995; Rutherford & Jones, 1992 [cross-sectional

analysis]) others do not (Blazevich et al., 1998; Henriksson-Larsén et al., 1992;

Rutherford & Jones, 1992 [longitudinal study]). The lack of pennation changes

with hypertrophy might be due to increases in the packing density of contractile

proteins which has been shown after resistance training (Claassen et al., 1989;

Horber et al., 1985; Jones & Rutherford, 1987), although the extent to which

packing density occurs is debated (Claassen et al., 1989). It is also possible that

pennation produces a ‘gearing’ effect rather than simply being a response to

muscle hypertrophy. Fibres of pennate muscles shorten less for a given tendon

excursion which would allow sarcomeres to work closer to their optimum length

during high-force contractions.

40

Given muscles that frequently perform high-force, low-velocity contractions tend to

have greater pennation and shorter fibres while the opposite is true for muscles

that perform low-force, high-velocity contractions, architectural adaptations could

occur with velocity-specific training. Architectural changes occur rapidly and could

therefore partly explain early adaptations to such training.

Muscle hypertrophy

The number of parallel sarcomeres in the muscle (Roy & Edgerton, 1991) largely

determines the force generated by a fully activated muscle. Either adding more

sarcomeres within muscle fibres or adding more fibres could increase the number

of parallel sarcomeres. Although increases in fibre number (hyperplasia) have

been shown in animal muscles (Gonyea et al., 1986; Tamaki et al., 1992) it is not

possible to directly determine whether the process occurs in humans.

Nonetheless, muscle size increases in resistance-trained subjects has been

associated with both fast-twitch and slow-twitch fibre hypertrophy (Alway et al.,

1992; Bell & Jacobs, 1990; Hortobágyi et al., 2000; MacDougall et al., 1984; Volek

et al., 1999). It has been suggested that the time course of hypertrophy is related

to the fibre type (Abernethy et al., 1994). Indeed, hypertrophy of fast-twitch fibres

may occur earlier in a strength training program (< 8 weeks) than hypertrophy of

slow-twitch fibres (Häkkinen et al., 1981).

Explosive-type training might cause preferential hypertrophy of fast-twitch fibres

(Esbjörnsson Liljedahl et al., 1996; Mero et al., 1983). Tesch et al. (1987) showed

increases only in type II fibres after heavy resistance and plyometric training.

Esbjörnsson Liljedahl et al. (1996) and Linossier et al. (1997) reported increases

in type IIb fibre area with increased power in a cycle sprint after sprint training.

Furthermore, changes have been shown, at least after short periods of training (4

weeks), to be greater in previously non-resistance trained women than men

(Esbjörnsson Liljedahl et al., 1996). Such findings have been attributed to women

having smaller fast-twitch fibre areas prior to training (Esbjörnsson Liljedahl et al.,

41

1996; Wang et al., 1993). In women, type I fibre areas are generally greater

than IIa and IIb while in men type IIa fibre areas are greater than IIb and I (in that

order [Simoneau et al., 1985; Staron et al., 1984; Staron et al., 1990]). Selective

hypertrophy of fast-twitch fibres might contribute to the velocity-specific

adaptations reported in the literature. Muscle protein synthesis is significantly

elevated within four hours of training (Chesley et al., 1992; MacDougall et al.,

1992, 1995) and increases in hypertrophy have been seen after training for as

little as four weeks (Esbjörnsson Liljedahl et al., 1996). Thus, selective

hypertrophy of fast-twitch fibres could be a factor in early velocity-specific

performance improvements.

Fibre-type transformation (MHC expression)

Eighty-five percent of the myosin molecule is composed of myosin heavy chains

(MHC; Whalen, 1985). The bending of the myosin molecule that pulls actin and

results in sarcomere shortening is performed by a combination of elastic distortion

and active rotation in the heavy chain. This occurs between the light chain (at the

head of the myosin molecule) and the catalytic domains of the myosin molecule

(Irving et al., 2000). Thus the maximum shortening speed of a muscle is possibly

affected by the expression of different MHC isoforms. These isoforms are shown

in Table 2.1. The type of MHC present in muscle is suggested to be a major

determinant of skeletal muscle function (Bottinelli et al., 1991; 1992; Green, 1992).

Muscle fibres that are predominant in the MHC I isoform exhibit slower shortening

velocities (Harridge et al., 1996; Larsson & Moss, 1993) and lower power outputs

(Bottinelli et al., 1996) than fibres predominant in the MHC II isoforms. Training

may alter this MHC expression. Tesch et al. (1989) showed that Olympic and

power lifters possessed a greater fast-twitch to slow-twitch fibre ratio than

bodybuilders. Saltin and Golnick (1983) also reported that successful power

athletes had a higher percentage of fast-twitch fibres in propulsive muscles. Such

differences suggest that either genetics or training influenced their fibre types.

42

Table 2.1. Myosin Heavy Chain isoforms in human skeletal muscle. There are also various

intermediaries, and other isoforms shown only in muscle from non-human animals.

Slow-twitch muscle Fast-twitch muscle

I IIa

Ic IIx or IId

IIb

IIeo, IIsf

Note: IIx/IId are the same myosin type thought to be a hybrid of IIa and IIb, IIeo refers to a type

found in extraocular muscle of humans, IIsf refers to a type found in the human jaw.

MHC changes have indeed been shown related to the training stimulus with

endurance-type exercise and some strength training regimes producing greater

type I MHC content (Adams et al., 1993; for reviews see Abernethy et al., 1994;

Jürimäe, 1997). While such changes may be related to the metabolic effects of

training, Pette and Vrbovà (1992) showed that low-frequency stimulation

transformed faster MHC types to slower types. Also, high-frequency stimulation

has been suggested to change slow-twitch fibres of the soleus muscle to fast-

twitch fibres (Ausoni et al., 1990; Gorza et al., 1988). These results suggest that a

mechanical stimulus, and the frequency of a muscle’s activation under the

stimulus (high/low frequency), might affect MHC expression.

Despite changes in MHC content after resistance training, these changes have

not been closely related to changes in maximal slow-speed strength (Jürimäe et

al., 1996; Carroll et al., 1998). Myosin heavy chain shift might be most closely

related to the velocity of training movements. Indeed Mannion et al. (1995)

showed that type II fibres increased in proportion with dynamic, high-intensity

exercise capacity. Other research has also showed decreases in type I and

increases in type II MHC isoforms after sprint cycle training (Jansson et al., 1990)

and combined sprint and resistance training (Andersen et al., 1994).

Nonetheless, Harridge et al. (1998) found no changes in MHC isoform expression

after six weeks of cycle sprint training. Training involved three-second sprint

intervals designed not to induce metabolic fatigue. The result suggests perhaps

that the mechanical stimulus was too low for changes to occur or that both

metabolic and mechanical factors contribute to MHC isoform expression.

43

Alterations in fibre-type have been seen after only two weeks of training in

humans (Staron et al., 1994), and after as little as four (Goldspink et al., 1991)

and ten (Ohira et al., 2000) days in animals. It is therefore possible that specific

myosin isoform changes could at least partially account for rapid improvements in

high-velocity force production.

Contractile Kinetics

The contractile apparatus consists of myosin, actin, tropomyosin, troponin C,

troponin I and troponin T (Gunning & Hardeman, 1991; Tsika et al., 1987).

Further, the myosin molecule is composed of two heavy chains (~200 000 Da

[daltons]) and four light chains ~20 000 Da). There are two different forms of light

chains, the phosphorylatable or regulatory (MLC2) and the alkali (MLC1 and

MLC3) light chain each with varying isoforms. It is on MLC 2 that the myosin

ATPase-mediated phosphorylation occurs that allows actin-myosin sliding. The

predominant isoform present in muscle is strongly related to its twitch force and

velocity (Jostarndt-Fogan et al., 1998; O’Brien et al., 1992). These isoforms are

summarised in Table 2.2.

Table 2.2. Contractile protein isoforms (not including MHC) in human skeletal muscle.

Protein Slow-twitch muscle Fast-twitch muscle

Regulatory light chain 2S, 2S’ 2F

Alkali light chain 1Sa, 1Sb 1F,3F

Actin ásk ásk

Tropomyosin â, áS â, áF

Troponin C S F

Troponin I S F

Troponin T S F

S = slow, F = fast.

The proportions of light chain (LC) myosin isoforms has been shown to change in

animal muscle. Cross-innervation of rabbit soleus resulted in increased fast LC

isoforms and decreased slow isoforms in both treated and contralateral limbs

44

(Srihari et al., 1981). Also, suspension of rats by their tails was associated with

increases in fast LC isoforms in the soleus, whereas 30 s sprint or endurance

training lead to a predominance of slow isoforms in the vastus lateralis

superficialis (Guezennec et al., 1990). Few studies have reported no changes in

LC isoforms after training (e.g. Bar et al., 1989).

While some research has shown that force development (and Ca2+ sensitivity) is

related to a muscle’s troponin isoforms (Geiger et al., 1999), it is likely that LC

isoforms are the greatest determinant. Lowey and colleagues (1993) showed that

the removal of the LC from myosin reduced actin sliding velocity from 8.8 to 0.8

microns.s-1 while there was no significant change in myosin ATPase activity.

Reconstitution of either the regulatory or alkali light chain caused moderate

increases in actin velocity while reconstitution of both LC’s restored original sliding

velocity. Thus the sliding velocity of actin was not related to myosin ATPase

activity but to the presence of light chains.

Moreover, the rate of phosphorylation of the regulatory LC is significantly related

to force and rate of force development in both isometric (Grange et al., 1995;

Sweeney & Stull, 1990) and dynamic (Grange et al., 1998) contractions. Fast-

twitch muscle has been shown to contain largely fast LC isoforms (Jostarndt-

Fogan et al., 1998). Indeed O’Brien et al. (1992) reported that proportions of slow

myosin heavy chain and LC isoforms in chronically-stimulated sheep latissimus

dorsi muscle were 86% and 92% respectively after 3 months. The slow form of

tropomyosin constituted only 64% and changes in troponin T were only significant

after 5 months of stimulation. Therefore changes in myosin heavy and light

chains preceded changes in tropomyosin and troponin.

Thus, the shortening velocity of a fibre is strongly related to the LC isoforms

present. Since the rate of phosphorylation of the LC influences the contractile

properties of a fibre, isoform changes have been seen in less than two weeks and

the presence of LC’s appears necessary for physiological speeds of sarcomere

45

shortening, changes in LC isoforms in muscle might largely explain velocity-

specific adaptations to training.

Muscle calcium kinetics

Calcium (Ca2+) release from and uptake to the sarcoplasmic reticulum influences

sarcomeric contraction force at submaximal contraction levels (Booth et al., 1997;

Ortenblad et al., 2000). Muscle fatigue that causes a decreased force output

(Booth et al., 1997; Tupling et al., 2000) or rate of force development (Ortenblad

et al., 2000) has been associated with reduced efflux of Ca2+ from, and re-uptake

to, the sarcoplasmic reticulum. Nonetheless, such changes have been shown not

to affect sarcomere relaxation time (Booth et al., 1997; Hunter et al., 1999). Also,

while increases in Ca2+ efflux are associated with higher contraction forces at

submaximal Ca2+ levels, it has not been shown that supra-physiological amounts

of Ca2+ improve contractile force above a sarcomere’s previous maximum.

Increases in Ca2+ release and repeated sprint performance have been shown with

sprint training (Duke & Steele, 2000). However the greater Ca2+ release might be

a response to other changes that have taken place in the sarcomere. For

example, greater phosphate availability induces Ca2+ release. Increased

phosphate results from increased myosin ATPase activity (which is higher in ‘fast’

fibres than ‘slow’ fibres). Indeed Geiger et al. (1999) showed that troponin

isoforms, which are related to the myosin heavy chain isoforms present in a

sarcomere, affect the Ca2+ sensitivity of the actin-myosin interaction. Thus

changes in Ca2+ availability after training might be related to the rate of cross-

bridge cycling (and therefore myosin ATPase activity) rather than being an

adaptation which in itself improves sarcomeric shortening speed.

Muscle-based Enzymes

Muscle-based enzymes act as catalysts for chemical reactions in muscle cells.

46

Increases in enzymes that speed reactions associated directly with muscle

contraction could therefore be considered beneficial to high-speed performance.

Some studies have reported increases in glycolytic enzymes after periods of

sprint-type training (Cadefau et a., 1990; Costill et al., 1979; Jacobs et al., 1987;

Roberts et al., 1982) while relatively few have not have not (Henriksson &

Reitman, 1976; Hickson et al., 1976). Nonetheless, enzymes whose activities

have been shown higher after sprint-type training include hexokinase,

phosphofructokinase, lactate dehydrogenase and creatine kinase (Dawson et al.,

1998; Hellsten et al., 1996; MacDougall et al., 1998). Greater activity of these

enzymes is not likely to result in increases in the contractile speed of a muscle,

but would result in increases in energy produced through glycolytic pathways and

allow a greater quantity of work to be performed in a short duration activity.

Myosin ATPase splits ATP to ADP and an inorganic phosphate prior to cross-

bridge interaction to provide energy for the conformational change in the myosin

molecule that pulls actin and results in sarcomere shortening. A muscle’s

contraction speed is significantly related to its fibre’s myosin ATPase activity

(Enoka, 1994; Báráry, 1967). Indeed ‘fast-twitch’ fibres are characterised by their

high quantity of myosin ATPase (Essén et al., 1975). Increases in myosin

ATPase activity have been reported in sprint-type training studies where training

bouts are brief (< 10 s; Dawson et al., 1998; Thorstensson et al., 1975)

suggesting that training can affect the enzyme’s activity. No changes were seen

after 12 weeks of high-intensity resistance training (Green et al., 1998).

Since both the size and number of type II fibres increase with high-velocity

training, the increase in total muscular myosin ATPase activity could be quite

large. Thus, while glycolytic enzyme activities are unlikely to affect absolute

muscle contraction speed, increases in myosin ATPase activity after training have

been thought a major contributor to the shortening velocity of sarcomeres.

Nonetheless, Lowey et al. (1993) showed that the removal of the light chains

(which are located on the myosin head) from the myosin molecule is associated

with dramatic decreases in sarcomere shortening velocity with no significant effect

47

on myosin ATPase activity. Thus there is at least some evidence that myosin

ATPase, while correlated with sarcomere shortening velocity, is not responsible

for regulating the shortening velocity of the sarcomere.

2.3.5 Summary

With respect to velocity specificity, results of studies investigating responses to

isokinetic training suggest that strength increases are greater at, and perhaps

slightly below, the movement velocities of the training exercises. When an

isotonic (isoinertial) training mode is used, subjects who perform movements at

higher velocities tend to perform better in tasks requiring higher movement speeds

(Wilson et al., 1993). It appears therefore that resistance training at movement

speeds approaching those of a sporting task are more likely to lead to task

improvement than resistance training at slow movement speeds. The

mechanisms responsible for velocity-specific performance changes are complex

and not well defined. It appears as though muscular factors such as architectural

changes (pennation and fibre length), fast-twitch fibre hypertrophy and transition

from slow light and heavy chain myosin isoforms to fast isoforms could explain

many of the early changes. The contribution of neural factors is less clear. While

some research suggests that increased motor unit recruitment and/or selective

activation of fast motor units might improve high-velocity force output as much

evidence questions their influence. Clearly more research is required with respect

to the time-courses of both neural and muscular changes before a complete

model of velocity-specific adaptations is possible.

48

2.4 BENEFITS OF RESISTANCE TRAINING TO HIGH-SPEED TASK

PERFORMANCE

2.4.1 Strength and mass of muscle and connective tissue

An increase in muscle mass is commonly observed with traditional forms of

resistance training (Alway et al., 1992; Bell et al., 1990; Kawakami et al., 1995;

Tracey et al., 1999). Given that the force generated by a muscle at maximum

stimulation is largely determined by the number of half sarcomeres arranged

parallel in a muscle (Roy & Edgerton, 1991), muscular hypertrophy could be

considered beneficial to power production during high-speed movements.

Furthermore, muscular hypertrophy often occurs with increases in the amount of

connective tissue within the muscle (Enoka, 1988; Kuno et al., 1990; Wang et al.,

1993). Force can be transmitted laterally in muscle (Huijing, 1999; Monti et al.,

1999; Street, 1983) so it has been suggested that the increase in connective

tissue might also improve strength (Jones et al., 1989). There might be a second

benefit to the increase in connective tissue with training however. Large forces

are imposed on tendons, muscles and ligaments (Behm, 1991) during high-speed

movements. Since strength training increases the strength and mass of

connective tissue, it may also enable the body to cope with the large forces of

high speed/explosive strength training (Miffed, 1988; O’Bryant et al., 1988). This

adaptation may benefit both injury prevention and the utilisation of stored elastic

energy in stretch-shorten cycle activities.

Increases in muscle activation have also been reported after resistance training

(Akima et al., 1999; Häkkinen & Komi, 1983, 1986; Ozmun et al., 1994). The

increase in activation is often attributed to either a greater number of active motor

units and/or an increase in their firing rate. However, much evidence for

increased activation has come from studies employing surface EMG techniques

(Häkkinen & Komi, 1983; 1986; Moritani & DeVries, 1979; Ozmun et al., 1994).

Many other researchers have shown no increases in EMG after resistance training

49

(Cannon & Cafarelli, 1987; Garfinkel & Cafarelli, 1992; Herbert et al., 1998;

Narici et al., 1996; Rich & Cafarelli, 2000) and some increases in EMG could

perhaps be a result of greater muscle synchronisation (Yao et al., 2000). Total

muscle recruitment using twitch interpolation (Brown et al., 1990; Carolan &

Cafarelli., 1992; Harridge et al., 1999; Herbert et al., 1998; Sale et al., 1992) and

tetanic stimulation (Davies & Young, 1983; Davies et al., 1985; McDonagh et al.,

1983; Young et al., 1985) has shown no changes in muscle recruitment with

training. Only recently has evidence from magnetic resonance imaging methods

supported the long-held belief that greater muscle activation results from

resistance exercise (Akima et al., 1999). Furthermore, strength increases have

been shown after twitch (Martin et al., 1994) and tetanic (Lyle & Rutherford, 1998)

stimulation of muscles where increases in muscle activation mediated by the

central nervous system are unlikely to have occurred. Thus it is still not clear

whether the ability to recruit motor units during maximal contractions is enhanced

by resistance training.

Increases in muscle strength may shift the force-velocity curve upwards. Humans

are unlikely to produce greater high-velocity force outputs than low-velocity force

outputs (despite some evidence that sprint runners produce greater isokinetic

force at 180o.s-1 than at 30o.s-1 [Alexander, 1990; Blazevich, 1995]). Thus,

improving the low-velocity area of the force-velocity curve might allow more scope

for force increases at high-velocities. This has prompted some authors to suggest

that strength gains from lower-velocity resistance training would allow more scope

for speed/power development, in advance of high-velocity training (Poliquin,

1992).

Heightened co-contraction can be expected during the performance of high-speed

(Karst & Hasan, 1987; Lestienne, 1979; Marsden et al., 1983) or repetitive,

alternating tasks (Cooke & Brown, 1990). Heightened co-contraction would

increase the energy cost of a task. It would be beneficial if muscular co-

contraction can be reduced in high-speed movements by resistance training.

Decreases in muscular co-contraction have been reported after periods of

50

isometric (Carolan & Cafarelli, 1992) and dynamic (Häkkinen et al., 1998;

Pousson et al., 1999) resistance training. However, only Pousson et al. (1999) has

provided evidence for such an occurrence after high-velocity training. Thus, little

evidence exists to suggest that changes in muscular co-contraction occur after

such training.

2.4.2 Consequences of Resistance Training for High-speed Task

Performance

While, in theory, the physiological changes that result from resistance training at

different movement velocities may aid the development of high-speed strength, it

is unclear whether resistance training improves speed or power performance

above those gains made by practicing the task (eg running, cycling, throwing etc.)

alone. Concurrently using high-velocity resistance training and task practice might

improve performance in that task more than using concurrent low-velocity

resistance training and task practice during short (seven week) training periods

(Blazevich, 1995). However, little research (e.g. Hoff & Almasbakk, 1995; Voigt &

Klausen, 1990) has demonstrated that the use of resistance training improves

performance more than task practice alone. While decreases in muscular co-

contraction have been shown after resistance training (Häkkinen et al., 1998;

Pousson et al., 1999), low-velocity resistance training could possibly promote non-

beneficial changes in the nervous system. Barrata et al. (1988) showed that co-

contractions during a slow (15o.s-1) isokinetic leg extension exercise were

increased (four-fold) in athletes who performed leg flexor resistance training (as

part of their own physical training; N=10) as compared to two groups who did not

perform leg flexor training (athletes, N=7 and untrained, N=7). Given that neural

adaptations, in response to resistance training, may occur within weeks (Moritani

& DeVries, 1979; Sale, 1987), it is plausible that even a short duration resistance

training program may increase levels of co-contraction, and therefore decrease

the efficiency of a fast, repetitive movement such as sprint running or cycling.

Resistance training has also been shown to elicit different architectural changes to

51

those thought optimum for high speeds of muscular contraction. Muscles that

often perform high-force, low-velocity contractions tend to possess short fibres

with large pennation (Burkholder et al., 1994; Van Eijden et al., 1997). The

opposite is common in muscles that often perform low-force, high-velocity

contractions. Indeed faster sprint runners have been shown to have muscles with

longer fascicles (commonly used as an estimate of fibre length) than slower sprint

runners (Kumagai et al., 2000). Such a result supports research findings that

longer fibres contract faster than shorter fibres (Sacks & Roy, 1982; Wickiewicz et

al., 1984). Despite muscles with lesser pennation and longer fibres perhaps being

best for high-speed task performance, resistance training has been shown to

promote the opposite (Blazevich & Giorgi, 2001; Kawakami et al., 1993; 1995).

Thus architectural adaptations to slow-speed resistance training might not be

conducive to high-velocity force production.

Finally, adaptations to resistance training have been shown specific to the

movement velocity (Caiozzo et al., 1981; Colliander & Tesch, 1990; Kanehisa &

Miyashita, 1983; Petersen, 1988), body position (Solomonow et al., 1986; Wilson

et al., 1996), joint angles or muscle lengths (Kitai & Sale, 1989; Weir et al., 1994),

laterality (Howard & Enoka, 1991; Tanaguchi, 1997) and contraction type (Lacerte

et al., 1992; Tomberlin et al., 1991) of the training movement. Thus the ‘transfer’

of strength gained in one task to another is often limited. Regardless of whether

resistance training has benefits and consequences for high-speed task

performance, one could question the likely performance improvements that would

result from resistance training. Despite this, resistance training is still commonly

performed by speed/power athletes providing anecdotal evidence at least that this

form of training has some benefits.

2.4.3 Summary

While high-velocity training is required for high-velocity strength adaptation, low-

velocity strength training may benefit high-velocity force development. Increases

in muscle strength, connective tissue strength and perhaps motor unit recruitment

52

may directly influence high-velocity force production. Further, low-velocity,

high-force resistance training may increase training variation when performed with

high-speed training to promote continuous improvements and avoid a plateau

(which is more likely to occur with a less variable training program). Therefore,

periodised training, which utilises high-force resistance training prior to, and

interspersed with, high-velocity resistance training may be beneficial for

speed/power development. Unfortunately, adverse physiological changes such as

increases in muscular co-contraction, increases in muscle pennation and

decreases in fibre length may, at least partially, negate the benefits of low-

velocity, high-force resistance training. Learning to effectively combine low- and

high-velocity resistance training with task practice may be the necessary step in

determining the ‘ideal’ training program for speed/power development.

2.5 IMPLICATIONS OF THE LITERATURE REVIEW

Athletes often use resistance training in an attempt to improve high-speed force

production since increases in muscle and tendon strength, the recruitment of

muscle fibres and increases in muscle size can improve dynamic force production.

Studies investigating neuromuscular and performance adaptations to RT have

shown the effects of altering the movement patterns and velocities at which

training. Nonetheless, research has not shown whether the benefits of RT

outweigh the costs when such training is used in a concurrent regime. Foreseeing

the likely outcomes of concurrent training is also difficult since the neuromuscular

adaptations to training are not well understood. Particularly, assigning neural

explanations (as apposed to muscular explanations, or a combination of the two)

as the cause of performance changes has been problematic. Given the inherant

difficulty in mimicing many sporting movements it is important that athletes and

coaches are informed of the importance of movement-specific training over the

general strength programs often used concurrently with speed/power training. It

would be of value to determine, 1) whether resistance training augments

performance in high-speed activities more than task training alone, 2) whether the

resistance training is required to have the same movement pattern as the task

53

being trained for, 3) whether the resistance training should be performed at a

velocity approaching that of the task being trained for, and 4) what mechanisms

underlie adaptations to concurrent speed and resistance training. Further

research is required to answer these questions.

54

CCHHAAPPTTEERR 33:: SSTTUUDDYY OONNEE

55

A COMPARISON OF MOVEMENT PATTERNS

OF THE VERTICAL JUMP, BROAD JUMP AND

ACCELERATION PHASE OF THE SPRINT RUN

TO THE SQUAT LIFT AND FORWARD HACK

SQUAT EXERCISES.

3.1 INTRODUCTION

Tasks such as the vertical jump, standing broad jump and sprint run are

commonly performed in many sports, as well as in studies investigating

human performance. Given that adaptations to resistance training are

specific to the movement patterns of the training exercises used (Abernethy &

Jürimäe, 1996; Rutherford et al., 1986; Wilson et al., 1996) it might be

important that training exercises aiming to improve these tasks, and tests

designed to assess performance, have similar movement patterns to the

tasks. With respect to movement-specific adaptations, past research has

shown that adaptations to training, in particular resistance training (RT), are

specific to the body position adopted (Abernethy & Jürimäe, 1996; Raasch &

Morehouse, 1957; Wilson et al., 1996), laterality (i.e. whether the exercise is

performed with one limb or two; Häkkinen et al., 1996; Howard & Enoka,

1991; Tanaguchi, 1997), joint ranges of motion (Kitai & Sale, 1989; Lindh,

1979; Weir et al., 1994) and the mode of contraction (Hortobágyi et al., 1996,

2000; Lacerte et al., 1992; Smith & Rutherford, 1995) of the training

exercises. There is a need therefore to examine the movement patterns of

athletic tasks and resistance training exercises in order to determine

differences in their movement patterns.

Several investigations have examined the movement characteristics of the

56

vertical jump (Bobbert et al., 1986, 1996; Eloranta, 1994; Pandy & Zajac,

1991; Voigt et al., 1995), broad jump (Robertson & Fleming, 1987), sprint run

(Mann & Herman, 1985; Mero & Komi, 1987; Simonsen et al., 1985) and

acceleration phase of a sprint run (Jacobs & Ingen Schenau, 1992; Mero &

Komi, 1990). Also, common resistance training tasks such as the squat lift

have also been well described (McCaw & Melrose, 1999; McLaughlin et al.,

1977; Ninos et al., 1997; Wretengeng et al., 1996). Nonetheless, few

researchers have compared and contrasted the movement patterns of athletic

tasks with movement patterns of resistance exercises (e.g. Canavan et al.

[1996] compared the Olympic clean movement to the vertical jump).

Furthermore, little attempt has been made to describe RT exercises that may

have similar movement patterns to athletic tasks by performing well-controlled

kinematic studies.

The first purpose of this study was to describe and compare the movement

patterns of athletic subjects performing vertical jump (VJ), standing broad

jump (BJ), squat lift (SQ) and jump-squat (JSQ) tasks. The term ‘movement

pattern’ will be used to describe only the timing and magnitude of joint angle

changes (with reference to angular velocities and accelerations) during a

movement. Thus no reference to body position or other factors describing a

movement pattern will be considered in this definition. A second purpose was

to compare the movement patterns of a new exercise, named the forward

hack squat (FHS), and the acceleration phase of a sprint run. Running

acceleration is essential to the performance of many sports so resistance

training exercises that can improve running performance would benefit many

athletes. The FHS was designed in an attempt to augment sprint running

improvements. The acceleration phase of a sprint run was chosen rather than

the maximum velocity phase since 1) the beginning of the acceleration phase

is easy to pinpoint considering it occurs when the subject’s velocity is zero; 2)

resistance training exercises that mimic the movement pattern of the

acceleration phase should be easier to design than those for the maximum

velocity phase; 3) many sports require participants to accelerate rapidly, but

57

not necessarily attain maximum speed; and 4) the acceleration phase of a

sprint run is more often used as a test of dynamic performance in research

studies. Due to space limitations in our laboratory, we were unable to

videotape and complete a kinematic analysis of sprint running. As such, the

kinematics of the FHS was compared to sprint running data published by

Jacobs and Ingen Schenau (1992). This was the only study found to provide

an extensive description of the early acceleration phase of sprinting (second

stance phase) rather than the maximum velocity phase or ‘block’ (starting)

phase. Subjects in that study were seven well-trained male sprint runners

(100 m time = 10.6 ± 0.2 s). Given the subjects in the present thesis were not

elite runners, it cannot be assumed that they would use the same technique in

the acceleration phase as those of Jacobs & Ingen Schenau (1992).

However, they were of similar height and age (see ‘3.2.1 Subjects’).

3.2 METHODS

3.2.1 Subjects

Eight male subjects (age = 25.1 ± [SD] 2.5 yrs, height = 1.81 ± 0.09 m, weight

= 96.3 ± 10.0 kg) volunteered for the study. This subject number was chosen

in order to gain a broad description of movement patterns for the chosen

tasks; many biomechanical analyses have used fewer than eight subjects

(e.g. Bobbert & Van Soest, 1994; Bobbert et al., 1996; Mero & Komi, 1987,

1994; Robertson & Fleming, 1987; Simonsen et al., 1985). The height and

age of subjects were similar to those presented in Jacobs and Ingen Schenau

(1992; age 23 ± 2 yrs, height = 1.84 ± 0.06 m) and would allow good

comparison of resistance training movement patterns to the acceleration

phase of the sprint run as described by those authors. All subjects had

performed regular, heavy weight training at least three times a week for at

least one year prior to participation in the study. They also regularly

participated in sports involving jumping and running. Prior to participation,

58

subjects were briefed on the study, read and signed statements of

Informed Consent and performed at least three familiarisation trials of each

test exercise. The study was approved by the Southern Cross University

Human Experimentation Ethics Committee (see Appendix A).

3.2.2 Overview

Subjects performed a standard warm-up including five minutes of stationary

cycling at a self-selected workload and three to five trials each of a VJ, BJ, SQ

with a load of 60% of bodyweight and FHS with no load added to the sled (the

FHS exercise is described later). Reflective markers were placed on the body

landmarks (see Table 3.1). Subjects then performed three maximal trials of

single- and double-leg VJ and BJ with their arms in different positions, SQ and

JSQ with different loads, and single- and double-leg FHS with different loads.

Subjects rated their performance in each trial and poor trials (i.e. those in

which the subject failed to perform maximally or considered himself

unbalanced) were repeated. The order of exercises was the same for all

subjects. To minimise fatigue subjects rested for one minute between trials of

the same task and three minutes between sets of different tasks. The

movements were recorded by a high-speed video camera (200 Hz) and data

sets relating to joint movement (joint angular displacement, velocity and

acceleration) were calculated after digitising joint markers using Peak Motus

software.

3.2.3 Videography

3.2.3.1 Body landmarks

59

After the standard warm-up, reflective markers (2 cm diameter) were

placed on landmarks on the subjects’ head, arms, trunk and legs (Table 3.1).

All markers were placed on the right side of the body and subjects performed

all movements with their right side to the camera. For SQ and JSQ, the 7th

cervical vertebra (C7) was obscured from view. Therefore, a rigid extension

was placed on the weightlifting bar that allowed an accurate estimation of C7

position. Calculation of C7 position by this method is described in detail later.

3.2.3.2 Camera set-up and video recording

A high-speed video camera (Peak HSC-200, Peak Technologies, Inc. USA)

operating at 200 Hz was placed 12 m from the subject and a one-metre scale

rod was placed at the subject’s feet for later calculation of the scaling factor.

A 1000 W lamp was placed adjacent to the camera and shone on the subject

to increase the contrast of the reflective markers relative to the background

(Burgess-Limerick et al., 1993). The camera was 1.8 m off the ground and

recorded the sagittal view to clearly capture the subject’s head (TMJ; Table

3.1) marker during the squat lift when weights on the bar often obscured it.

The distant camera positioning (12 m) was used to minimise parallax error

created by the high placement of the camera. Camera settings are described

Table 3.1. Landmark names and marker positions forreflective markers.

Landmark Marker PositionHead Temporomandibular joint (TMJ)Neck 7th Cervical vertebra (C7)Shoulder Glenohumeral jointElbow Elbow axisWrist Ulnar styloidAnterior pelvis Anterior superior iliac spinePosterior pelvis Posterior superior iliac spineHip Greater trochanterKnee Femoral condyleAnkle Lateral malleolusHeel Lateral posterior calcaneusToe Metatarsal head II

60

in Table 3.2. These settings allowed high resolution of markers and

optimum field of view for capturing the movements. Once the video was set

up for each subject, the camera was not moved or adjusted for the duration of

testing.

Prior to each task being performed, subjects were viewed at 50 Hz on a

Gateway EV 700 Monitor (Gateway, USA) to ensure the subject was in full

view of the camera. The frame rate was then increased to 200 Hz and the

images of tasks recorded on videotape (Panasonic XD Pro S-VHS,

Panasonic, Japan). Recording began two seconds prior to each movement

and ended two seconds after completion. Video images were recorded by a

Panasonic AG 5700 videocassette recorder (Panasonic, Japan) for later

analysis.

3.2.4 Description of movement tasks

3.2.4.1 Vertical jumps

Subjects performed three trials of a single-leg jump with arm swing and three

trials of four different double-leg countermovement vertical jumps. The hand

positions were varied across trials; the VJ techniques are described in Table

3.3. Changing the hand positions was expected to alter the distance of the

body’s centre of mass from the hip joint and possibly change the movement

pattern adopted by the subjects. It would then be possible to compare the

movement patterns used in performing these different jumps to the movement

Table 3.2. Camera settings during dataacquisition.

Characteristic Camera settingFrame rate 200 HzShutter speed 1/1000 sAperture 2.8 f-stopsFocal length 3×Distance (d) 12 m

61

pattern used to perform the squat exercises.

On instruction the subjects performed the designated jump for maximum

height; a countermovement was allowed prior to the upward. Subjects

descended until their internal knee angle was approximately 100o (± 10o).

Jumps were practiced prior to testing however no mechanical device was

used to ensure the correct knee angle was adopted. Trials where the knee

angle varied by more than 10o from the requested angle were disqualified

from later analysis.

3.2.4.2 Broad jumps

One version of a single-leg BJ and three versions of the double-leg BJ were

performed. The jumps are described in Table 3.4. Subjects performed three

trials of each jump for maximum horizontal distance. No other stipulation was

made regarding the jump’s performance so the subjects performed the jumps

naturally.

Table 3.3. Description of vertical jump techniques. The jumps were performed in the orderpresented here.

Jump DescriptionSingle-leg with arm swing Jump was performed unilaterally. The arms were free to

swing during the jump.Double-leg with arm swing Jump was performed bilaterally. The arms were free to swing

during the jump.Double-leg with hands onhead

Jump was performed bilaterally. The hands were placed onthe head and the elbows faced forward to stop the TMJmarker being obscured.

Double-leg with armsacross chest.

Jump was performed bilaterally. The arms were crossed overthe chest with hands on opposite shoulders. The right wristwas supinated to ensure the wrist marker was visible duringthe jump.

Double-leg with hands onhips

Jump was performed bilaterally. Hands were placed on thehips at the level of the Iliac crest so that the pelvic/hip markerswere not obscured.

62

3.2.4.3 Free-weight barbell squat lift

Subjects performed three squat lifts at each of three weights. First, weights

were placed on a 20 kg Olympic weightlifting bar such that the combined load

equalled 60% of bodyweight. With the loaded bar resting across the

shoulders level with the 7th cervical vertebra (C7), subjects squatted until the

internal knee angle was approximately 100o before moving back to the

starting position. Pilot testing showed that subjects often perform

countermovement jumps to a 100o knee angle. As such, movement

instructions for the SQ and VJ movements were the same. Subjects had

practiced lowering the weight to a knee angle of 100o during the warm-up and

lifts were disqualified from analysis if the knee angle was not within 10o of the

stipulated angle. The subjects were also asked to perform the movement in a

total of two to four seconds with equal time devoted to the downward and

upward phases. After three trials, they repeated the efforts with loads equal

to 100% and 140% of bodyweight. It was hypothesised that changing the

weight lifted would change the movement pattern used for the task since the

centre of mass of the weight-body system would be higher at the higher loads.

Table 3.4. Description of broad jump techniques. The jumps were performed in the orderpresented here.

Jump DescriptionSingle-leg with arm swing Jump was performed unilaterally. The arms were free to

swing during the jump.Double-leg with arm swing Jump was performed bilaterally. The arms were free to swing

during the jump.Double-leg with armsacross chest.

Jump was performed bilaterally. The arms were crossed overthe chest with hands on opposite shoulders. The right wristwas supinated to ensure the wrist marker was visible duringthe jump.

Double-leg with hands inhips

Jump was performed bilaterally. Hands were placed on thehips at the level of the Iliac crest so that the pelvic/hip markerswere not obscured.

63

3.2.4.4 Jump-squat

Three repetitions of a JSQ were performed with a load equal to 60% of

bodyweight. Thus comparisons were possible between JSQ and SQ

movement patterns since both were performed with a load of 60% of

bodyweight. The JSQ was performed similarly to SQ except subjects

performed the concentric phase of the movement with maximal effort. As

such the subject’s feet left the ground during the upward phase. As for VJ,

subjects were asked to descend until the internal knee angle was 100o and

jump for maximum height. Trials where the knee angle varied by more than

10o from the requested angle were disqualified from later analysis.

3.2.4.5 Forward hack squat (FHS)

The FHS was performed in a semi-prone position by lowering and raising a

weight placed on a sled that moves on rails. The exercise was called the

‘forward hack squat’ because the direction of the movement of the weight is

similar to the semi-supine hack squat exercise performed by many weight

trainers. The double-leg FHS is shown in Figure 3.1 and the single-leg

variation is shown in Figure 3.2. Subjects performed five different FHS tasks

including double-leg FHS with 60%, 100% and 140% of bodyweight added to

the 74 kg sled and single-leg FHS with no weight and 50% of bodyweight

added to the sled. Despite the different movement characteristics of SQ and

FHS exercises, pilot testing in our laboratory showed that forces produced at

loads of 60%, 100% and 140% of bodyweight were similar for the SQ and

FHS exercises.

64

Subjects lowered the weight until their internal knee angle was 100o and then

lifted the weight back to the starting position. A 100o knee angle was chosen

since research by Jacobs and Ingen Schenau (1992) showed this to be the

smallest knee angle achieved during the acceleration phase of a sprint run,

and subjects moved to this knee angle during the VJ and SQ exercises. Thus

more accurate comparisons could be made between the FHS, SQ, VJ and

sprint movements. While the eccentric phase was completed in one to two

seconds (so that the contribution of the stretch-shorten cycle to the movement

was consistent across trials) the concentric phase was always performed in

less than one second. For the single-leg FHS (Figure 3.2), the ‘free’ leg was

extended straight backwards during the eccentric phase but became flexed at

the hip and knee during the concentric phase.

Figure 3.1a. The forward hack squat (FHS)

exercise was performed in a semi-prone

position by first lowering a sled (onto which

weights were placed) until the internal knee

angle was approximately 100o. The sled is

placed on rollers and moves along a central

rail. Notice that the internal hip angle is less

than 90o in this position.

Figure 3.1b. After lowering the sled it was

then moved back to the starting position in

preparation for the next repetition.

65

3.2.5 Analysis of video data

The video recordings of each trial were replayed and captured as digital video

by a computer and marker positions digitised using Peak Motus software

(Peak Performance Technologies, USA). Spatial models were designed as

described below and a calibration factor was calculated by the software after

digitisation of the scale rod. Calibration was performed for every movement

for every subject since the subjects’ positions at the beginning of the

movement could not be held perfectly constant. The digitised data was

scaled according to the calibration factor and filtered to remove high

frequency noise before missing data was interpolated and new data sets

formed (see below). From the new data sets, angular displacement, velocity

and acceleration were calculated and compared between tasks.

3.2.5.1 Spatial model

A spatial model was designed to describe the body landmarks, body

segments and joint angles. Body landmarks corresponding to the marker

Figure 3.2. The single-leg forward hack squat was performed as per the double-leg

version except that the ‘free’ leg is extended behind the body in the descending phase and

then flexed (as seen here) in the ascending phase. As such, the movements of the legs

are more similar to those in the acceleration phase of sprint run.

66

placements described above were defined. From these, body segments

and joint angle definitions were described as shown in Tables 3.5 and 3.6

respectively. For the squat lift and jump-squat tasks, the C7, wrist, elbow and

shoulder markers were obscured by the weights added to the bar. In the

spatial model for the squat lifts, these markers were not described, but were

labelled and designated as a ‘virtual point’. The positions of these markers

were estimated by an alternate method (see below).

3.2.5.2 Calculation of virtual point position

A 40 cm inflexible extension was placed on the centre of the bar and

protruding perpendicularly from it. Two reflective markers of 1.5 cm diameter

were set 29.2 cm (proximal marker) and 38 cm (distal marker) from the outer

border of the bar on the side opposite to the extension (see Figure 3.3). The

Table 3.6. Joint angle definitions.

Joint angle DefinitionPelvis-thigh Angle calculated clockwise from pelvis segment to thigh segment. Hip

flexion decreases the angle.

Hip Vector from the knee to greater trochanter to C7. Hip flexion decreasesthe angle.

Knee Anatomical 180o angle between the greater trochanter, knee and ankle.Knee flexion increases the angle.

Ankle Anatomical 90o angle calculated clockwise from the foot segment to the legsegment. Dorsiflexion decreases the angle.

Table 3.5. Body segment definitions.

Segment label Proximal marker Distal markerHead/neck C7 Temporomandibular joint (TMJ)Trunk C7 Greater trochanterUpper arm Shoulder ElbowForearm Elbow WristPelvis Anterior superior iliac spine Posterior superior iliac spineThigh Greater trochanter Knee

Leg (shank) Knee Ankle

Foot Heel Toe

67

markers formed a straight line and the bar rested on the C7 vertebra (the

position of the bar was checked prior to all SQ and JSQ trials) so that a ‘virtual

point’ could be calculated that was situated on the line made by the markers

and at a distance of a certain number of multiples of the distance between the

two markers. These markers were digitised, their raw coordinates exported to

a spreadsheet and the coordinates of the virtual point calculated. The x-

coordinate was calculated by the equation:

x-coordinate = [(xdist – xprox) × 3.32] + xprox ....................(1)

where xdist is the horizontal distance (distance in the x plane) from the bar to

the distal bar extension marker, xprox is the horizontal distance from the bar to

the proximal bar extension marker, and 3.32 represents multiples of the

distance between the two markers described above and shown in Figure 3.

The y-coordinate was similarly calculated by the equation:

y-coordinate = [(ydist – yprox) × 3.32] + yprox .................... (2)

where ydist is the vertical distance (distance in the y plane) from the bar to the

distal bar extension marker, yprox is the vertical distance from the bar to the

A

Reflective markers placed 29.3 cm and 38cm from the opposite surface of the weightbar (point A).

Bar extension (40 cm long).

Figure 3.3. A bar extension was placed on the weight bar. Reflective markers placed onthe bar were later digitised. The position of C7, shoulder, elbow and wrist landmarkswere calculated by equations (1) and (2) and imported into the original filtered data setsas ‘virtual’ point data.

68

proximal bar extension marker, and 3.32 represents the multiples of the

distance between the two markers as described above and shown in Figure

3.3. Once the x- and y-coordinates of the virtual point were calculated, the

data were imported back into the trial data. A moving stick figure was created

from the raw data and the movement of the virtual point inspected to ensure

its correct calculation. The virtual data were used for the coordinate positions

of the C7, shoulder, elbow and wrist markers. While the bar rested across the

shoulders and was placed adjacent to the C7 vertebra, and the wrist marker

was in close proximity to the bar, the elbow was approximately 10 - 15 cm

from the bar. The distance from the elbow to the bar was minimised by

subjects placing their hands wide on the bar, however some error would have

occurred when using the virtual data as a description of the location of the

elbow joint. The error was consistent across all SQ and JSQ trials since the

subject’s hand positions were held constant.

3.2.5.3 Digitisation procedure

After the spatial model was described a 0.05 s segment of video sequence

containing the scaling rod was captured. The scaling rod was manually

digitised and a calibration factor calculated by the software. Subsequently, a

three second segment of video of the same movement, encapsulating one

subject performing one task, was captured and cropped approximately 0.1 s

(equal to 20 frames) either side of the start and end points of the movement.

Landmarks were digitised using the auto-tracking facility with parabolic

automatic point prediction. The automatic digitisation procedure was watched

carefully to ensure marker confusion did not occur and markers were not

digitised when invisible (i.e. markers positions were not guessed when

obscured from view). Gaps in the raw position data that resulted from these

periods of marker obscurity were filled by mathematical interpolation (Peak

Motus, Peak Performance Technologies, USA) when the period of marker

obscurity lasted less than one-sixth of movement time. Trials were discarded

from analysis if gaps longer than one-sixth of movement time were found for

any marker.

69

Raw data sets (including virtual point data) for all tasks were filtered using a

4th order, zero-lag Butterworth filter with a 6 Hz cut-off frequency. A cut-off

frequency of 6 Hz was chosen since the movement frequencies of human

subjects rarely exceed this value. A cut-off frequency of 6 Hz has been used

previously when analysing human lifting techniques (Burgess-Limerick et al.,

1993; Kromodihardjo & Mital, 1987) and similar cut-off frequencies have been

used in the analysis of high-speed movements (Gregor et al., 1985; Vint &

Hinrichs, 1996; Voigt et al., 1995). The filtered, raw coordinates were scaled

using the previously determined scaling factor and calculations of joint angular

displacements, velocities and accelerations performed.

3.2.6 Statistical Analysis

Means and standard deviations were calculated for joint angle, angular

velocity and angular acceleration data sets from the eight subjects. To

compare movements two methods were used. First, the times to complete

16%, 33%, 50%, 66% and 84% of a movement were calculated and graphed

against movement time (normalised to 100% of movement time). For this

analysis, the first and second phases of a movement were calculated

separately such that mid-movement occurred at 50%. Then 16% and 33% of

movement were calculated at 33% and 66% of the first (descending) phase.

66% and 84% of movement were calculated at 33% and 66% of the second

(ascending) phase. For example, if the knee angle for a movement moved

through a range of motion of 60o during the descending phase (i.e. 0 – 60o of

knee flexion) and then 70o (60 – -10o) during the ascending phase of a

movement, then 16%, 33%, 50%, 66% and 84% of the total movement

occurred at 20o, 40o, 60o (during knee flexion), 46.2o and 23.1o (during knee

extension).

The second method used to compare movements was by statistical analysis.

There are several methods that can be used to compare curves, however

70

none are without fault. For simplicity, curves were broken into sections

representing 5% of movement time and compared using paired t-tests (since

the same subjects performed all movements). This method has been used

previously in research investigating the sprint run (Weimann & Tidow, 1995).

Due to the large number of t-tests, the Bonferroni-corrected alpha level was

reduced to 0.0025 (for an overall alpha level of 0.05) making significant

differences very difficult to detect and the statistical analysis overly

conservative. In such instances (i.e. where the universal null hypothesis is not

of interest) Bonferroni correction is not warranted as important information

may be lost after analysis (Perneger, 1998). Thus Bonferroni correction was

not performed.

3.3 RESULTS

3.3.1 General Movement Descriptions

The movement patterns of subjects performing SQ, FHS, VJ and BJ tasks are

shown in Figures 3.4 – 3.7. Only one version of each exercise will be

described here, a comparison of different versions of each exercise will follow.

In these figures a decrease in angle of the hip and ankle joints represents joint

flexion, while an increase in knee joint angle represents joint flexion. This is

because the internal hip and ankle angles, but the external knee angle, are

shown to minimise overlap of hip and knee graphs and improve clarity.

Nonetheless, for all joints (hip, knee and ankle) an increase in angular velocity

or acceleration is shown as a positive inflection in the graph.

3.3.1.1 Squat lift

The movement pattern of a SQ performed with a load equal to bodyweight

resting across the shoulders is shown in Figure 3.4. The general movement

patterns for squats with loads of 60% and 140% were similar and therefore

71

will not be presented here. From the starting (standing) position the hip, knee

and ankle joints flexed simultaneously and the body moved to a squatting

position. The angular acceleration of the joints was small throughout this

descending phase. At the transition from descending to ascending phases

the hip and knee angles (mean ± SD) were 92 ± 9o and 98 ± 7o (82o internal

knee angle) respectively. Ankle dorsiflexion was greatest at –30 ± 6o at this

transition point. Almost as a mirror image of the descending phase, the

ascending phase was also characterised by simultaneous extension of the

hip, knee and ankle joints and no rapid accelerations. The body finished in

the original, upright position.

-50

0

50

100

150

200

Join

t Ang

le (

deg)

-150

-100

-50

0

50

100

150

200

Join

t Ang

ular

Vel

ocity

(deg

.s-1

) Hip

Knee

Ankle

-2000

-1500

-1000

-500

0

500

1000

1 26 51 76 101 126 151 176 201Jo

int A

ngul

ar A

ccel

erat

ion

(deg

.s-2

)

Time (0.5% intervals)

-50

0

50

100

150

200

Join

t Ang

le (

deg)

-150

-100

-50

0

50

100

150

200

Join

t Ang

ular

Vel

ocity

(d

eg.s

-1) Hip

Knee

Ankle

-2000

-1500

-1000

-500

0

500

1000

1 26 51 76 101 126 151 176 201

Join

t Ang

ular

Acc

eler

atio

n(d

eg.s

-2)


Figure 3.4. Movement pattern of the squat liftexercise. The exercise is characterised bysimultaneous movements of the hip, knee andankle joints. The angular velocities of these jointsmirrored each other although higher angularvelocities occurred at the knee because of itslarger range of motion. Error bars representstandard deviation.

Figure 3.5. Movement pattern of the forwardhack squat (FHS) exercise. While similar to thesquat lift, ankle plantarflexion occurred after hipand knee extension. Thus the FHS appears ahybrid of push-like and throw-like movementpatterns. Error bars represent standard deviation.

72

3.3.1.2 Forward Hack squat

The movement pattern for a bilateral FHS with a weight equal to bodyweight

placed on the sled of the machine is shown in Figure 3.5. The different

movement pattern adopted during FHS compared to SQ was expected given

the constraints of the FHS machine. Similar to SQ the hip, knee and ankle

joints flexed simultaneously. However while the hip angle reached a minimum

of 102 ± 13o (i.e. only slightly more open than during SQ) the smallest knee

angle was 81 ± 7o (99o internal knee angle), 17o more closed than for SQ.

Therefore, compared to SQ, the movement pattern of FHS is one where hip

flexion is greater than knee flexion in the descending phase of the movement.

The ankle range of motion was also different. While identical minimum ankle

angles were achieved during both SQ and FHS tasks (the minimum ankle

angle for FHS was 30 ± 6o), ankle plantarflexion occurred much later in the

FHS movement. The different timing of ankle angle changes can be observed

clearly in the angular velocity and acceleration graphs. The increase in

angular velocity and acceleration occurred after the peak in hip and knee

angular velocity and acceleration. Therefore, while movement about the hip

and knee joints occurred simultaneously, movement at the ankle was delayed.

3.3.1.3 Vertical jump

The movement pattern for a VJ with arms placed across the chest (VJ ac) is

shown in Figure 3.6. Unlike the RT exercises, a larger proportion of the

movement time was devoted to the descending phase of the movement as a

consequence of the high vertical velocity of the centre of gravity achieved

during the ascending phase. The magnitude of joint angle changes however

were similar to those of SQ (the smallest hip, knee and ankle angles were 98

± 10o, 97 ± 9o and 33 ± 4o respectively). Possibly the most striking difference

between the VJ and resistance exercises was the timing of joint angle

73

changes. In the VJ, the hip angular velocity increased before the knee and

ankle (middle graph, Figure 3.6) although all joints reached their peak angular

velocity at the same time (immediately prior to toe-off). Thus the VJ

movement pattern exhibited sequential extension of joints from proximal to

distal consistent with a throw-like movement.

3.3.1.4 Broad jump

The movement pattern for a BJ with arms placed across the chest (BJ ac) is

presented in Figure 3.7. Similar to the VJ, angular accelerations and

velocities were far higher than for the resistance exercises, however the


-50

0

50

100

150

200

Join

t Ang

le (

deg)

-400

-200

0

200

400

600

800

Join

t Ang

ular

Vel

ocity

(deg

.s-1

) Hip

Knee

Ankle

-10000-8000-6000-4000-2000

0200040006000

1 26 51 76 101 126 151 176 201

Join

t Ang

ular

Acc

eler

atio

n

(deg

.s-2

)

-50

0

50

100

150

200

Join

t Ang

le (

deg)

-400

-200

0

200

400

600

800

Join

t Ang

ular

Vel

ocity

(deg

.s-1

) Hip

Knee

Ankle

-10000-8000

-6000-4000-2000

02000

40006000

1 26 51 76 101 126 151 176 201

Join

t Ang

ular

Acc

eler

atio

n

(deg

.s-2

)


Figure 3.6. Movement pattern of the verticaljump. The exercise was characterised by largeaccelerations of the hip, knee and ankle joints.The angular velocities of these joints reached theirmaxima simultaneously. Error bars representstandard deviation.

Figure 3.7. Movement pattern of the broad jump.The hip extended early in the ascending phase toreach a higher angular velocity than the knee andankle joints. Error bars represent standarddeviation.

74

changes in joint angles were unlike any other movement described thus

far. The hip angle rapidly closed during the descending phase, followed later

by the knee then ankle joints. The smallest hip angle was 85 ± 20o in the

transition from descending to ascending phases. While this is smaller than for

other movements it was highly variable. The knee and ankle angles later

closed to 82 ± 14o (98o internal knee angle) and -36 ± 7o respectively. The

ascending phase began with rapid extension of the hip joint (see middle and

bottom graphs, Figure 3.7) before the lagging knee and ankle joints extended.

Unlike all other movements, the highest angular velocities occurred at the hip,

rather than the knee. Thus, while the BJ was similar to the VJ in that joint

extensions occurred sequentially, the BJ movement pattern was very different

to the other movements described previously.

3.3.2 Comparisons of Task Movement Patterns

Comparisons between tasks are shown in Figures 3.8 – 3.13. Each

movement is divided into the phases previously described. For example, the

16% bin on the x-axis represents that part of the movement where subjects

were 16% of their way through the total movement, or 33% of their way into

the descending phase. The 50% mark represents the transition period

between descending and ascending phases. The 84% mark represents that

part of the movement where subjects were 84% of their way through the total

movement, or 66% of their way through the ascending phase. The phase of

movement is plotted against the total movement time (y-axis). As such, these

are displacement versus time graphs. A steep gradient suggests that the

subjects were moving slowly (i.e. they took more time to move through the

movement phases). In contrast, a flatter gradient suggests that subjects were

moving more quickly in that part of the movement (that is, they moved

considerable distance in little time). Error bars were omitted to improve

clarity. Further statistical comparisons will be presented later.

75

3.3.2.1 Squat lift comparisons (SQ versus JSQ)

The movement pattern of JSQ differed from the traditional squat lifts (SQ +

60% and SQ + 140%; squat with a load of bodyweight is not shown) in that

the descending phase was performed slower than the ascending phase (see

Figure 3.8). Also, while the relative timing of hip angle changes was similar to

the traditional squats, both knee and ankle joint extension was delayed. That

is, the JSQ knee and ankle curves rise early suggesting relatively slower

movement, then flatten toward the end of the movement suggesting more

rapid joint angle changes. The size of this effect was greater for the ankle

than the knee suggesting a sequential extension of joints from hip to ankle.

Thus the movement pattern of the JSQ was different to the traditional squat

lifts.

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

FHS 1lFHS + 60%

FHS + BW

0%

20%

40%

60%

80%

100%

16% 33% 50% 66% 84%

% Total Movement Time

Knee

Ankle

0%

20%

40%

60%

80%

100%

FHS 1L

FHS + 60%FHS + BW

0%

20%

40%

60%

80%

100%

16% 33% 50% 66% 84%

Phase of Movement

% T

otal

Mov

emen

t Tim

e

Knee

Ankle

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

JSQ

SQ + 60%SQ + 140%

0%

20%

40%

60%

80%

100%

16% 33% 50% 66% 84%

Phase of Movement

Ankle

Knee

% T

otal

Mov

emen

t Tim

e

Hip

Figure 3.8. Comparison of the jump-squat (JSQ),and squat lifts with 60% (SQ + 60%) and 140%(SQ + 140%) of bodyweight across the shoulders.

Figure 3.9. Comparison of single-leg forwardhack squat (FHS 1L) and forward hack squatswith 60% (FHS + 60%) and 100% (FHS + BW) ofbodyweight added to the sled.

Hip

76

While there was little difference between either of the traditional squat lifts, the

ascending phase of the heavier lift (SQ + 140%) was slower (ie the curve

steeper) than for the lighter squat lift. Such a result would be expected given

the extra force required to move the heavier load.

3.3.2.2 Forward hack squat comparisons

Movement pattern differences between the FHS movements were perhaps

more numerous than for SQ (see Figure 3.9). The single-leg FHS differed to

the lighter FHS (FHS + 60%) in that the ascending phase was longer (ie the

curve was flatter between 50% and 100% of the movement) and

plantarflexion tended to occur more consistently rather than undergoing rapid

acceleration later in the movement. The single-leg FHS also differed to the

heavier FHS (FHS + BW) in that plantarflexion was more consistent. As such,

the single-leg FHS exhibited a very distinct push-like pattern of movement.

There were differences between the two double-leg FHS movements with

knee and ankle motion being slightly delayed early in the descending phase at

the lighter weight (FHS + 60%). There were however no significant

differences between the two tasks in the ascending phase.

3.3.2.3 Vertical jump comparisons

There were few differences between the movement patterns of the vertical

jumps where arms were not free to swing (i.e. on head, chest or hips),

therefore only the VJ with arms across chest and with arm swing are shown in

Figure 3.10. The two movements differed in that hip extension was delayed

at the transition phase and occurred rapidly later in the ascending phase in VJ

with arm swing (VJ wa). There was also a small difference at the ankle with

extension occurring later and more rapidly when the arms were free to swing.

77

Thus, although there were no differences at the knee, there were

differences in the timing of hip extension between the two VJ techniques.

3.3.2.4 Broad jump comparisons

There was little difference between those BJ where arms were (broad jumps

with arm swing; BJ wa) and were not (broad jump with arms across chest; BJ

ac) used. However, like VJ, hip extension was delayed early in the ascending

phase and more rapid toward the end when the arms were free to swing

(Figure 3.11). There were differences however between the double-leg and

single-leg (single leg broad jump; BJ 1L) jumps. Movements at the hip, knee

and ankle joints were more consistent in their changes for the single-leg jump

rather than showing periods of slower and more rapid change.

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

VJ ac

VJ wa

0%

20%

40%

60%

80%

100%

16% 33% 50% 66% 84%

Hip

Knee

Ankle

% T

otal

Mov

emen

t Tim

e

Phase of Movement

% T

otal

Mov

emen

t Tim

e

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

Bj 1LBj acBj wa

0%

20%

40%

60%

80%

100%

16% 33% 50% 66% 84%

Phase of Movement

Ankle

Knee

Hip

Figure 3.10. Comparison of vertical jumps witharms across the chest (VJ ac) and with arm swing(VJ wa).

Figure 3.11. Comparison of single-leg broadjump (BJ 1L), broad jump with arms across thechest (BJ ac) and broad jump with arm swing (BJwa).

78

3.3.2.5 Vertical jump versus jump-squat

Given the similar magnitudes of joint angle changes between VJac (VJ with

arms across chest) and JSQ, the two tasks were compared for their timing of

joint angle changes. As shown in Figure 3.12, there was little difference

between the movement patterns of the two tasks although relative velocity of

the joint angle changes during the descending phase of the JSQ was slightly

different. This may have been expected given the joint angles of the two

tasks differed slightly at the start of movement causing joint angle changes in

the JSQ to be slightly smaller than for VJac. There was no difference in the

timing of joint angle changes in their ascending phases.

3.3.2.6 Broad jump versus forward hack squat

As the body position during ascending phases of FHS and BJ were similar,

the timing of joint angle changes were compared (see Figure 3.13). There

appeared to be no similarity between the two movements. Their descending

phases were likely to exhibit different movement patterns given that the body

position during the descending phase of a FHS was semi-prone whereas the

body was upright during the BJ. However differences, although minimal at the

ankle, also existed during the ascending phase where the body position and

goal (direction of movement) of the tasks were similar. The FHS cannot

therefore be considered similar to BJ.

79

3.3.2.7 Similarities between squat lift and vertical jump tasks

Given the apparent similarity between different vertical jumps and between VJ

and SQ/JSQ, these movements were further analysed. The joint angle

changes for the VJ with arm swing and with arms across the chest are shown

in Figure 3.14. The significant effect of arm swing on hip range of motion can

be seen with differences (not corrected for experiment-wise error rate)

between the tasks occurring throughout the movement.

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

16% 33% 50% 66% 84%

0%

20%

40%

60%

80%

100%

FHS + BW

BJ ac

Phase of Movement

Ankle

Knee

% T

otal

Mov

emen

t Tim

e

Hip

Phase of Movement

% T

otal

Mov

emen

t Tim

e

0%

20%

40%

60%

80%

100%

0%

20%

40%

60%

80%

100%

VJ acJSQ

0%

20%

40%

60%

80%

100%

16% 33% 50% 66% 84%

Ankle

Hip

Knee

Figure 3.13. Comparison of forward hack squatwith a load equal to bodyweight added to the sled(FHS + BW) and broad jump with arms across thechest (BJ ac).

Figure 3.12. Comparison of the vertical jump witharms across chest (VJ ac) and jump-squat (JSQ).

80

Both of these jumping styles were compared to the SQ and JSQ. There were

large differences between the VJ with arm swing and all of the squat tasks.

However there was little difference between movement patterns for VJac and

JSQ (Figure 3.15). Other vertical jumps without arms swing (i.e. with hands

on head and with hands on hips) were not as similar as VJac. The main

differences between VJac and JSQ were at the beginning of the movement

(see Figure 3.15). The hip and knee joints were more flexed during a JSQ

possibly due to the load lifted. However, as the movement proceeded the

plots of the joint angles merge. Indeed there was little difference in the joint

angles of hip, knee and ankle between the movements both at the transition

from descending to ascending phases, and during the entire ascending

phase. Differences in the ascending phase were limited only to the point

immediately before toe-off where extension of the hip and ankle joints was

more complete during the VJ. Thus, subjects adopted similar movement

patterns for the performance of JSQ and VJac.

Figure 3.14. Comparison of vertical jumps with arm swing (VJwa) and vertical jumps witharms across chest (VJ ac). Both the timing and magnitude of hip joint angle changes weredifferent between the two tasks (* indicates p<0.05). There was little difference at the kneeand ankle joints although the vertical jump with arms across the chest was characterised byslightly less plantarflexion at the end of the ascending phase (# indicates p<0.05). Error barswere omitted to aid readability but standard deviations were similar to those in Figure3.7.

-50

0

50

100

150

200

0 20 40 60 80 100

Percent of Movement Time (%)

Join

t Ang

les

(deg

rees

)Hip angle VJwa

Knee angle VJwa

Ankle angle VJwa

Hip angle VJ ac

Knee angle VJ ac

Ankle angle VJ ac

*

#

*

*

81

3.3.2.8 Similarities between the forward hack squat and acceleration

phase of sprint running

Given the dissimilarity of FHS and BJ movement patterns, the timing and

magnitude of joint angle changes for the concentric phase of a FHS were

compared to those of the acceleration phase of a sprint run described by

Jacobs and Ingen Schenau (1992). While the data for the sprint run were not

available, some comparisons could be made to the joint angle curves

presented by the authors (Figure 3.16). There appeared to be good

agreement in the joint angle curves for the hip and knee joints. Both tasks

were characterised by smaller joint angle changes early in the concentric

phase but more rapid changes later. Further, the joint angular velocity curves

(curves for the sprint run are not presented here) were similar in that the

-50

0

50

100

150

200

0 20 40 60 80 100

Percent of Movement Time (%)

Join

t Ang

les

(deg

rees

)

Hip angle JSQ

Knee angle JSQ

Ankle angle JSQ

Hip angle VJ ac

Knee angle VJ ac

Ankle angle VJ ac

*

*

+

#

#

Figure 3.15. Comparison of the jump-squat (JSQ) and vertical jump with arms across chest (VJ ac).While there is a small but significant difference in joint angles at the start of the movements, their timingof joint angle changes, and magnitude of joint angles at the point of transition from descending toascending phases are almost identical. Subjects starting from a more upright position in the JSQ couldmake the two tasks more similar. * - hip angles significantly different, + - knee angles significantlydifferent, # - ankle angles significantly different (p<0.05). Error bars were omitted to aid readability, butstandard deviations were similar to those presented in figures 3.5 and 3.7.

82

greatest angular velocities occurred at the knee joint. The hip and knee

joints attained their maximum angular velocity simultaneously with the

maximum at the ankle occurring marginally later. Greater differences were

seen in the range of motion of the ankle with plantarflexion being greater at

the start and end of the concentric phase in the sprint run. In order to perform

the FHS more similar to the sprint run, subjects could have plantarflexed more

at these points during the movement.

Joint angles during a Forward Hack Squat with weight

1

1.5

2

2.5

3

3.5

Hip

Ang

le (

radi

ans)

1

1.5

2

2.5

3

3.5

Kne

e A

ngle

(ra

dian

s)

1

1.5

2

2.5

3

3.5

0 20 40 60 80 100

Percent of Push-off Time (%)

Ank

le A

ngle

(ra

dian

s)

Joint angles during a sprint push-off. Adapted from Jacobs and Ingen Shenau,

1992.

1

1.5

2

2.5

3

3.5

Hip

Ang

le (

radi

ans)

1

1.5

2

2.5

3

3.5

Kne

e A

ngle

(ra

dian

s)

1

1.5

2

2.5

3

3.5

180 160 140 120 100 80 60 40 20 0

Time (ms)

Ank

le a

ngle

(ra

dian

s)

Figure 3.16. Comparison of joint angle changes for the forward hack squat (FHS) andacceleration phase of a sprint run (adapted from Jacobs & Ingen Schenau, 1992). Anglesare presented in radians as per Jacobs & Ingen Schenau (1 radian = 57.3o). Hip and kneepatterns were very similar while the ankle angle differed largely at the start and end of thepushing phase.

83

3.4 DISCUSSION

The purpose of this study was to compare the movement patterns of subjects

performing VJ and BJ to their movement patterns during the squat lift (SQ and

JSQ) and FHS exercises. This discussion will not directly compare the

movement patterns of these tasks to those described in previous studies, but

focus on comparing the movements presented here with the aim of finding

resistance exercises that are similar in movement pattern to the VJ and BJ,

and the acceleration phase of the sprint run.

The VJ is performed bilaterally and in an upright position and was therefore

first compared to the SQ. During the descending phase of the VJ, joint angle

changes occurred simultaneously with flexion of the hip, knee and shoulder

joints. However these joints opened sequentially (from hip to ankle) during

the upward phase. Nonetheless, the angular velocities of these joints

reached their maxima simultaneously immediately prior to toe-off. Such a

movement pattern has been previously reported for the vertical jump (Bobbert

et al., 1986; Pandy & Zajac, 1991; Voigt et al., 1995).

Since two different styles of VJ were analysed, one where the arms were free

to swing (vertical jump with arm swing; VJwa) and the other where the arms

were held stationary (in fact three versions of the latter were also compared),

variations of the VJ were examined. Most notably, the two jumping styles

differed in that the hip angle of VJwa was smaller (more closed) at the

transition from descending to ascending phases. While its effect has not been

directly examined in the literature, the increase in range of motion of the hip

would possibly cause an increase in hip extensor moment. Some authors

have suggested that the increased hip moment, or rather the increase in joint

power from this, would be transferred by biarticular muscles to the ankle

culminating in an increase in ankle plantarflexor moment and an increase in

jump height (Bobbert & Ingen Schenau, 1988, 1992; Van Soest et al., 1993).

84

SQ was often performed by simultaneous flexion of the hip, knee and ankle

joints during the descending phase and then simultaneous extension during

ascent. The timing of joint angle changes was therefore different to either of

the two VJ styles. Although there was a difference in the hip angle at

transition from descending to ascending phases between VJ and SQ, there

was little difference between the magnitude of joint angle changes. However,

it cannot be concluded that the movement patterns adopted during VJ and SQ

tasks were the same.

There was little difference between movement patterns of JSQ and VJac.

Since the jump-squat is performed with a maximal ascending phase, the JSQ

and VJac had the same sequence of joint angle changes (i.e. hip before knee

before ankle). Furthermore, as illustrated in Figure 16, there was little

difference in joint angles at the transition from descending to ascending

phases. Probably the greatest difference between the two tasks was at the

movement’s beginning where joints were more closed during the JSQ. This

was likely a result of subjects squatting slightly under the load of the barbell

prior to the jump. Nonetheless, VJac could be considered very similar to the

JSQ since they were both performed bilaterally, in an upright body position

and the magnitude and timing of joint angle changes were very similar. How

the movement pattern of subjects performing the JSQ would change if heavier

loads were used is unclear from the present research.

The BJ is performed bilaterally from an upright position although the

ascending phase has a large horizontal component. In contrast to previous

research (Robertson & Fleming, 1997), the hip, knee and ankle joints

extended sequentially during the ascending phase. However, as reported

previously, the change in hip joint angle (and possibly contribution to total

torque) was far greater than the change at the knee (Robertson & Fleming,

1997) although the knee angular velocity was very high (Aguado et al., 1997).

As it is difficult to perform the SQ with such a movement pattern the FHS was

analysed and subjects’ movement patterns compared to those for the BJ.

85

BJ’s performed with arm swing were different to those without in that the

hip angle was lesser at the transition from descending to ascending phases.

The movement pattern of the double-leg BJ exhibited a sequential pattern

rather than they’re being simultaneous joint angle changes. These

characteristics are the same for the FHS so it was compared to the BJ.

The double-leg FHS was characterised by simultaneous extension of hip and

knee joints, but delayed ankle extension making it a hybrid of the throw-like

and push-like movement patterns often used to describe movements. The

single-leg FHS was characterised by simultaneous extension of the hip and

knee joints but a slower and more consistent change at the ankle joint. The

magnitude of joint angle changes were however not different between one-

and double-leg versions. The movement patterns of the FHS and BJ were

therefore not the same. Also, the magnitude of joint angle changes between

the FHS and BJ was very different. Thus, despite the two tasks being similar

in their laterality (i.e. both tasks can be performed unilaterally or bilaterally)

and the body position adopted during the ascending phase, the timing and

magnitude of joint angle changes were very different. The movement pattern

that characterised the FHS was therefore different to the BJ.

Given the dissimilarity of the FHS and BJ, the FHS was compared to the

acceleration phase of a sprint run. Due to space limitations in our laboratory,

the sprint run could not be kinematically analysed. Therefore the movement

pattern of the FHS was compared to the previously published data of Jacobs

and Ingen Schenau (1992). Qualitative comparison on the timing and

magnitude of joint angle changes for the two tasks showed that their

movement patterns were more similar than to the VJ or BJ. The greatest

difference between the two tasks was at the end of the push-off phase of both

movements where the sprint run is characterised by more prominent ankle

plantarflexion. Nonetheless, subjects in the present study performed the FHS

task without any instruction as to the level of plantarflexion required.

Plantarflexion at the end of the movement could probably be increased

86

significantly by these subjects without affecting the movement pattern of

the hip and knee joints.

The hip and knee joints extend simultaneously early in the push-off phase of

sprinting presumably to rotate the body forward before more rapid and

sequential extension of all three joints occurs later in the movement (Jacobs &

Ingen Schenau, 1992). A similar timing of joint angle changes was seen in

the ascending phase of the FHS. Further, the time at which the maximum

angular velocity of the joints occurred was also identical. Given therefore that

the timing and magnitude of joint angle changes were similar (and could be

made more similar with greater plantarflexion late in the pushing phase of the

FHS), both tasks can be performed unilaterally and the body is semi-prone in

the pushing phase of both movements, the movement pattern adopted for the

FHS and acceleration phase of sprint running appear very similar. Research

using the same subjects performing both tasks is necessary to more precisely

examine similarities and differences between the two movements.

In conclusion, the movement patterns of different exercises changed as the

constraints of the exercises (i.e. use of arm swing, load lifted, laterality, etc.)

were changed. This increased the number of movement patterns that could

be compared in order to find resistance exercises that could be considered

similar to VJ, BJ, and the acceleration phase of sprint running. Indeed, the

JSQ was very similar to the VJ without arm swing (especially when the arms

were crossed over the chest), although the effect of lifting greater JSQ loads

was not addressed in this study. Also, within the confines of the research

performed, one might conclude that the movement patterns of the FHS and

acceleration phase of a sprint run are also very similar. Given the movement

pattern specific adaptations to RT, the newly developed FHS exercise may be

a superior training exercise than SQ, JSQ or VJ to enhance sprint running

acceleration.

87

CCHHAAPPTTEERR 44:: SSTTUUDDYY TTWWOO

88

RELIABILITY AND VALIDITY OF ISOMETRIC

SQUAT AND FORWARD HACK SQUAT TESTS

4.1 INTRODUCTION

Research studies investigating adaptations to weight training often

incorporate the barbell squat as a dominant training exercise (Baker et al.,

1994; Delecluse et al., 1995; Häkkinen & Komi, 1983; Häkkinen et al., 1985a;

Thorstensson et al., 1976; Willoughby, 1993; Young & Bilby, 1993).

Nonetheless, despite research suggesting that the mode (contraction type:

isometric, concentric, eccentric) and movement pattern of strength tests

should be similar to those of the training exercises (for reviews see:

Abernethy et al. [1995] and Morrissey et al. [1995]), relatively few studies use

the 1-RM (one repetition maximum) squat test to determine strength changes

after training (Thorstensson et al., 1976; Willoughby, 1993; Young & Bilby,

1993). Instead, strength changes after squat lift training are often examined

by isometric tests (Häkkinen & Komi, 1983; Häkkinen et al., 1985a, 1987;

Young & Bilby, 1993) which may be preferred for their high test-retest

reliability (Agre et al., 1987; Bemben et al., 1992; Young & Bilby, 1993),

relatively simple administration and reduced risk of injury.

The relationship between dynamic strength increases and isometric strength

is not strong (Baker et al., 1994; Sale et al., 1992). For example, Sale et al.

(1992) found that isometric knee extension strength did not increase after a

19 weeks of leg press training despite muscle hypertrophy occurring over the

training period. Such results are possibly due to the different contraction

modes of training and testing exercises. However, the weak relationship

between changes in the isometric and dynamic tests may also be related to

their different movement patterns. A large body of evidence suggests that

89

adaptations to resistance training are specific to the movement pattern of

the training exercises (Abernethy & Jürimäe, 1996; Rutherford & Jones, 1986;

Thepau-Mathieu et al., 1988; Wilson et al., 1996). Thus, if isometric tests of

strength are to be used in preference to dynamic tests, or to assist in the

provision of training loads, it may be important that the body position adopted

in the isometric test be identical to the training exercise.

Given the SQ is commonly used in studies investigating adaptations to

resistance training, an isometric squat test (ISQ; figure 4.1A) might be a

useful alternative to the 1-RM squat. However, the movement pattern of SQ

is not similar to movements performed in many sports. The isometric FHS

(IFHS; Figure 4.1B) may be used since it allows isometric testing with a

movement pattern similar to sprint running (see Study One).

The purpose of this study was first to examine the reliability of both the ISQ

and IFHS tests to determine if repeated measures on the same subjects

AB

Figure 4.1. Subject position for both the isometric squat (ISQ; A) and forward hack squat

(IFHS; B) tests.

90

yielded reliable results, and second to examine the relationship between

isometric and 1-RM measures of strength. The ISQ test was performed with a

knee angle of 90o and the IFHS test with a hip angle of 90o so that the

subjects were in the lowest position of the movement. It was hypothesised

that the isometric force would be best related to dynamic 1-RM at this position

since it is here that the lifts are most difficult. This study is important in the

context of the thesis since a training study will be conducted. If isometric tests

can be used to predict 1-RM, training loads can be set with minimal effort or

injury risk and an indication of changes in subjects’ 1-RM strength could be

gained.

4.2 METHODS

4.2.1 Subjects

Fourteen athletic males (Age range = 19 – 26 yrs) volunteered to participate in

the study. All played competitive sport at a recreational or representative

level and had at least six months of weight training experience. The research

was approved by the Southern Cross University Human Ethics Committee

and subjects signed a statement of informed consent. They were able to

withdraw from the study at any time.

4.2.2 Testing

Subjects performed ISQ and IFHS tests on two occasions at the same time of

day one week apart. Subjects also performed a 1-RM squat or FHS test on

different testing days so that after two weeks each subject had performed

both the 1-RM squat and FHS tests once. The order of testing was

randomised between subjects to prevent order effects although isometric tests

were always performed before 1-RM tests. All tests followed a warm-up

91

including five minutes of moderate intensity running, ten minutes of

stretching and several warm-up repetitions of squat and FHS exercises at

increasing intensity.

4.2.2.1 Isometric squat (ISQ)

Subjects squatted until the internal knee angle was 90o with a 20 kg bar

resting across the shoulders. While in this position, the hip angle was

measured and recorded. Subjects then moved to a Smith Machine (a squat

rack designed to allow the bar to move only in the vertical plane) and squatted

with its bar across their shoulders until their hip and knee angles were

identical to the barbell squat. Metal stops were then placed on top of the bar

to prevent its upward movement. Once bar height was established, subjects

performed two warm-up trials of the isometric squat, one at 60% and one at

80% of their perceived maximum exertion (Figure 4.1). They then performed

three maximal isometric efforts lasting four seconds with three minutes rest

separating each trial. Hip and knee angles were checked prior to each effort

and loud verbal encouragement was given to increase subject motivation.

Force produced during the squat was recorded by a force platform (Kistler

Instrumenté, Switzerland) on which the subject’s feet were placed during each

isometric effort. The position of the feet was recorded for subsequent efforts.

Force was sampled at 1000 Hz and stored on computer (IBM compatible 486

DX) for subsequent analysis.

4.2.2.2 Isometric forward hack squat (IFHS)

The rails along which the sled moves were adjusted to an angle of 39o to the

horizontal. Subjects placed two feet on the foot platform such that the body

formed a straight line from the head to the ankle while in the standing position.

They then lowered the weight until the internal hip angle was 90o and the

92

internal knee angle was 110o (Figure 4.1B). This approximated the hip and

knee angles during push-off in the acceleration phase of sprint running

(Jacobs & Ingen Schenau, 1992). A metal peg was used to hold the machine

in this position for the subsequent maximal isometric contractions. Subjects

then lifted the sled slowly until the metal peg stopped its upward movement

and hip and knee angles were checked to ensure they were at 90o and 110o

respectively before the subjects provided two warm-up (60% and 80% of

perceived maximum) and three maximal isometric contractions lasting four

seconds. Three minutes rest separated each maximal effort. Force produced

during the isometric contraction was sampled at 100 Hz by a load cell (Output

= 1.9231 mV/V, hysteresis <0.02%, Model LPS-2KG, Scale Components Pty.

Ltd., Australia) placed parallel to the direction of sled movement. The signal

was fed into a personal computer (IBM compatible 486 DX) and data stored

for later analysis using a custom program written using AMLAB software

(Chatanooga, Inc., USA).

4.2.2.3 1-RM squat

1-RM squat strength (free-weight) was tested by subjects lifting increasingly

heavy weights until a weight could not be lifted. Subjects placed their feet

with the same stance as for the ISQ test and stood with a loaded barbell

across the shoulders. Subjects then squatted until their internal knee angle

was 90o before lifting the weight back to the standing position. The smallest

increment in weight between lifts was 5 kg. At least three minutes separated

each trial.

4.2.2.4 1-RM forward hack squat (FHS)

The position of the subjects’ feet and body, and of the rails on which the sled

moved, were identical to the IFHS. Each FHS trial required the subject to

lower the weight until their internal knee angle was 110o before lifting the

93

weight back to the standing position. Subjects attempted to lift

incrementally heavier weights until a weight could not be lifted. At least three

minutes separated each attempt and the smallest increase in weight between

successive lifts was 10 kg.

4.2.3 Data analysis

Change in the mean between testing session one and two, typical error (i.e.

variance of the change in performance between the two testing sessions),

Pearson’s Product Moment Correlations and Intraclass Correlation

Coefficients (ICC’s) were calculated as outlined by Hopkins (2000). After

curve-fitting procedures were used to ascertain the linear relationships

between the data (SPSS v10.0, SPSS Inc.), validity statistics including

Pearson’s correlations and linear regression equations with standard error’s of

the estimates were calculated. For reliability and validity statistics, 95%

Confidence intervals (95% CI) were calculated for relevant data. Finally,

paired t-tests with Bonferroni correction were used to compare observed and

predicted (from regression equations) 1-RM test scores to examine

differences between data sets. Alpha was set at 0.1 to reduce the likelihood

of type II error (finding no difference between observed and predicted values

when a difference existed).

4.3 RESULTS

4.3.1 Reliability of ISQ and IFHS

Reliability statistics for ISQ and IFHS are presented in Table 4.1. For ISQ,

there was a small and non-significant increase in force produced in the

second testing session (26.9 N or 0.9% of 2321 N). The reliability of the test

was very high with ICC = 0.97 and typical error of only 69 N. For IFHS, there

94

was a small and non-significant decrease in the force produced in the

second testing session (26.9 N or 1.2% of 2335 N). The test-retest reliability

of the test was also very high with an ICC = 1.00 and typical error only 30 N.

Thus, the two isometric tests were very reliable.

FHS Mean LCI UCI Squat Mean LCI UCI

∆ mean (N) -21.0 -62.7 20.7 ∆ mean 26.9 -42.0 95.9

Typical Error 29.9 21.5 49.4 Typical Error 68.7 48.7 116.7

Peason’s r 0.99 Peason’s r 0.97

ICC 1.0 0.99 1.0 ICC 0.97 0.91 0.99

4.3.2 Validity of isometric measures

There was a significant relationship between the average ISQ (average of

testing week one and testing week two) and 1-RM squat performance, and

average IFHS and 1-RM FHS performance (see Table 4.2). There was

however a poor correlation between subject performances in ISQ and IFHS

tests and only a moderate correlation between 1-RM squat and FHS test

performances. Therefore subjects who performed well in the isometric tests

also performed well in the dynamic tests but subjects who performed well in

the squat tests did not necessarily perform well in the FHS tests.

Table 4.1. Reliability statistics for ISQ and IFHS. Both tests show high reliability. ∆ mean –change in the mean from test week 1 to test week 2, ICC – Intraclass Correlation Coefficient,LCI – lower limit of confidence interval (95%), UCI – upper limit of confidence interval (95%).

Table 4.2. Pearson’s correlations for test performances. Thesquat lift was highly correlated with the ISQ. FHS was highlycorrelated with the IFHS. Lower correlations were foundbetween squat and FHS.

95

Test comparisons r R2 p-value

ISQ versus squat 0.77 0.61 <0.01

IFHS versus FHS 0.76 0.59 <0.01

ISQ versus IFHS 0.47 0.23 >0.1

Squat versus FHS 0.55 0.30 >0.05

Force produced during isometric contractions was converted to weight in

kilograms and compared to individual’s 1-RM lifts. On average, ISQ lifts were

147% of those on the 1-RM and IFHS lifts were only 89% of the 1-RM. Linear

regression equations to predict 1-RM performance from isometric

performance are presented in Figure 4.2. The standard error of the estimate

for ISQ was 13.8 kg (95% CI = 10.9 – 18.6 kg) and for IFHS was 19.4 kg

(95% CI = 15.4 – 26.2 kg). These standard errors represent 8.5% and 7.3%

of the average performance in 1-RM squat and FHS respectively. There was

no significant difference between predicted and obtained values for the data

presented here.

96

4.4 DISCUSSION

4.4.1 Reliability and validity

The results of the present study suggest that the reliability of both the

isometric squat (ISQ) and isometric forward hack squat (IFHS) tests are very

high (ICC = 0.97 & 1.00 respectively). These intra-class correlation

y = 0.0432x + 163.85

R2 = 0.5747

0

100

200

300

400

0 1000 2000 3000 4000

Average Isometric FHS (N)

1-R

M F

HS

(kg

)

y = 0.0356x + 78.67

R2 = 0.5856

0

100

200

300

400

0 1000 2000 3000 4000

Average Isometric Squat (N)

1-R

M S

qu

at (

kg)

Figure 4.2. Scatterplots of isometric versus 1-RM test performance. The linear regressionequations and R2 values are indicated on the graphs. Almost 60% of the variation in 1-RMperformance can be accounted for by isometric test scores.

97

coefficients are similar to those previously reported for isometric (0.85 –

0.99 [Agre et al., 1987; Bemben et al., 1992; Viitasalo et al., 1981; Wilson et

al., 1993]) and 1-RM tests (0.92 – 0.98 [Henessey & Watson, 1994; Hoeger et

al., 1990; Hortobágyi et al., 1989; Sale, 1991]). The difference in mean

performance (shift in the mean) between repeated test occasions was less

than 1.5% of the average performance. For the subjects tested here

therefore, there was little or no difference between performances at each

testing occasion despite the complex multi-joint coordination required to

perform the present tests. This suggests that the isometric tests used in the

present study would be able to detect small changes in isometric strength

between subjects or after some form of intervention.

There was also a strong relationship between subject scores in the isometric

tests and the associated 1-RM tests (rsquat = 0.77, rFHS = 0.76; p<0.01) with

over 60% of the variation in 1-RM tests explained by subject’s isometric

performances. Thus, subject scores in the isometric tests were strongly

related to their 1-RM scores. Furthermore, there was no significant difference

between values predicted by regression equations and those obtained by

testing of subjects’ 1-RM. Isometric measures could then be considered good

indicators of dynamic performance.

Nonetheless, the correlations obtained here were less than 0.8 and could not

be considered indicative of high validity. R2 values for the correlations

between isometric and 1-RM tests suggest that up to 40% of the variance in

1-RM performance could be explained by factors other than isometric

performance (see Table 4.2). Furthermore, while the standard errors of the

estimates for the relationships between the isometric and 1-RM tests were

small (SEEsquat = 13.8 kg, SEEFHS = 19.4 kg), they still represent 8.5% and

7.3% of the average 1-RM score for the squat and FHS respectively. Thus

there is some error in predicting 1-RM performance from isometric

performance using the tests presented here. While performance in the

isometric tests could be used as a good indication of a subject’s 1-RM

98

performance, and this performance could be predicted well from the

regression equations, precise estimates of 1-RM performance were not

possible.

4.4.2 Movement specificity

Of importance also is the weak relationship between subjects’ performances

in the squat and FHS tests. Those subjects who performed well in the squat

tests did not necessarily perform well in the FHS tests (risometric = 0.47, r1-RM =

0.55). Given the tests involve the same contraction modes (either isometric

[isometric tests] or an eccentric phase followed immediately by a concentric

phase [1-RM tests]), differences between test performances could be

attributed to their different movement patterns. The principle of movement

specificity has been shown extensively by past research (Abernethy &

Jürimäe, 1996; Baker et al., 1994; Blazevich & Gill, 2001; Blazevich et al.,

2000; Morrissey et al., 1995; Wilson et al., 1996). In the present study, high

force production in one posture was not always complemented by high force

production in the alternative posture suggesting an effect of movement pattern

on test performance.

4.4.3 Practical applications

The isometric squat and FHS tests were highly reliable and a strong

relationship existed between isometric and 1-RM performance. The ISQ and

IFHS tests could therefore be used to assess dynamic strength changes with

training. Given their high reliability, they could certainly be used to examine

changes in isometric strength between subjects, or after intervention.

However, the validity of the tests was moderate (r<0.8) and the number of

subjects tested here reasonably small. Caution should then be exercised

when trying to predict a subject’s precise 1-RM from isometric measures.

Furthermore, if the isometric tests were to be used to estimate changes in 1-

99

RM strength following intervention, the number of subjects would have to

be larger than if a 1-RM test was used. The increase in subject number would

equal 1/R2 (Hopkins, 2000), which for the ISQ test is 1/0.59, or 1.7, times the

subject number. Increasing subject numbers would increase the power of the

tests to nullify the loss of power caused by the moderate relationship between

the test types (lower validity of the isometric measures). Finally, subjects who

produced high forces in one posture (e.g. squat) did not necessarily produce

high forces in the other posture (e.g. FHS). Therefore, to best detect

performance changes with training, or differences between subjects, that test

which best matches the training movement patterns should be used.

4.4.4 Future research

Given the moderate validity of the isometric tests for estimating 1-RM

performance, some modifications could be made to the tests to improve their

validity. One change might be to vary the joint angles at which the test is

performed. In the present study, joint angles were chosen such that muscle

lengths were long and the forces relatively low. However, Sale (1991)

suggested that test variability was reduced when measurements were taken

at the strongest point in the range of motion. Moreover, Murphy et al. (1995)

found that the elbow angle in a bench press-specific isometric test affected

the relationship between isometric and 1-RM strength. The authors indicated

that tests should be performed at the joint angle at which peak forces were

provided. Thus, changing the joint angles adopted for the present isometric

tests may improve their validity.

Future research should also examine the relationship between these isometric

tests and their associated 1-RM tests by investigating the relationship

between changes in isometric and 1-RM strength after a period of resistance

training. While a highly reliable and valid isometric test should measure

performance similarly to its comparable dynamic test, this is not always the

case. Baker et al. (1994) found that a 27% improvement in 1-RM squat and

100

9% improvement in isometric leg extension force after squat training were

unrelated (r = 0.16, p>0.05). This was despite significant correlations (r =

0.57 – 0.61) between the variables pre- and post-training which would have

indicated moderate validity. Such results are possibly due to the different

contraction modes between training and testing exercises. Nonetheless, the

low relationship between changes in the isometric and dynamic tests may be

related to their different movement pattern. The movement patterns of the

isometric tests used in the present study were similar to their 1-RM

counterparts, thus minimizing the differences between tests. However, it is

still unclear whether changes in ISQ and IFHS test performance would be

related to 1-RM squat and FHS test performance after a period of resistance

training.

4.4.5 Conclusion

The isometric squat and forward hack squat tests were highly reliable (>0.97)

and would therefore be able to detect small differences in multi-joint isometric

strength between subjects, or performance changes over time. They are well

related to their 1-RM counterparts (SQ and FHS) with significant correlations

found between the test pairs (p<0.01). However, validity correlations were

only moderate (rsquat = 0.77, rFHS = 0.76). Therefore it is unclear whether

these tests can discriminate small changes in dynamic strength. Although 1-

RM strength can be estimated well from the regression equations, precise

estimates of 1-RM strength were not possible. Future research should

examine the relationship between changes in 1-RM and isometric

performance after a period of training to determine whether movement-

specific isometric exercises such as those presented here can be used to

detect small changes in dynamic performance.

101

CCHHAAPPTTEERR 55:: SSTTUUDDYY TTHHRREEEE

102

RELIABILITY OF UNILATERAL AND

BILATERAL FORWARD HACK SQUAT TESTS

5.1 INTRODUCTION

Much research has investigated differences in force production between uni-

and bilateral movements. For example, Secher et al. (1976, 1978) reported

that maximal, voluntary, isometric strength of the leg extensors was greater

(115% and 123% for 1976 and 1978 studies respectively) under bilateral

conditions. More recently, Häkkinen et al. (1996) and Tanaguchi (1997)

showed that bilateral strength increased more in subjects who trained

bilaterally while unilateral strength improved most in subjects who trained

unilaterally. These specific changes appeared similar for different exercise

tasks (hand grip strength, leg extensor power and arm extensor power;

Tanaguchi, 1997). Such evidence has lead researchers to suggest that

adaptations to uni- and bilateral training are dissimilar. Also, the maximum

voluntary force that can be produced by a limb depends on whether a

unilateral or bilateral task is used in testing.

Given the laterality specificity of performance, testing of performance changes

after bilateral training should probably be done using bilateral tests. Also,

unilateral changes should be assessed by unilateral tests. However, while

bilateral testing protocols are common, and reliability and validity studies have

supported their use as testing tools (e.g. Arnold & Perrin, 1993; Rahmani et

al., 2000; Steiner et al., 1993; Wilhite et al., 1992), it is unclear if unilateral

tests show the same reliability. Unilateral pushing tasks are less commonly

performed and balance during unilateral tasks may be more difficult to

maintain. The reliability of unilateral tasks could therefore be lower than

bilateral tasks.

103

To the author’s knowledge, no research has compared the reliability of

unilateral and bilateral tests. Inspection of research that has included both

unilateral and bilateral testing has either shown that variability of

performances were similar between the two types of tasks (Häkkinen et al.,

1996; Howard & Enoka, 1991) or that perhaps bilateral tasks showed more

variability (Tanaguchi, 1997). Furthermore, variability of jump height, work,

joint torque and joint power values appeared similar for one- and two-legged

jumps (Van Soest et al., 1985). Thus, while no research has specifically

tested the hypothesis, it appears likely that uni- and bilateral tests of

performance would be equally reliable.

The purpose of the present study was to examine the reliability of test

performances in the dynamic forward hack squat task. The forward hack

squat was chosen as the test exercise since no reliability studies have been

performed for dynamic contractions and, given its novelty, subjects would be

unlikely to be accustomed to its movement pattern. While the reliability of

isometric FHS has been previously shown (Study Two), the reliability of

dynamic squats has not. As an adjunct, reliability will be measured with two

different loads placed on the machine to determine whether the load lifted (or

the velocity of the movement) affects the test’s reliability.

5.2 METHODS

5.2.1 Subjects

Eleven active, male subjects volunteered for the study (Age = 20.5 ± 1.1 yrs).

Subjects signed statements of Informed Consent and were free to discontinue

the study at any time. The research was approved by the Southern Cross

University Human Research Ethics Committee prior to the commencement of

testing.

104

5.2.2 Protocol

Subjects participated in two identical testing sessions separated by one week.

In each session, testing was preceded by a five minute cycle at a self-

selected workload and two sets of two-legged forward hack squats with a self-

selected weight (equal to approximately 50% and 100% of bodyweight).

Cycle workload and weight lifted in the forward hack squat were recorded for

the first session and repeated in the second session.

5.2.3 Determination of testing loads

After warm-up, subjects performed two maximal, bilateral isometric

contractions lasting three seconds with hip and knee angles of 90o and 100o

(internal angle) followed by two unilateral contractions using the subjects’

preferred legs. The rails of the forward hack squat machine were aligned at

49o to the horizontal. Bilateral contractions were always performed before

unilateral contractions. Force produced by the subjects during the isometric

contractions was measured by a load cell placed in series with the movement

direction of the weighted sled (Output = 1.9231 mV/V, hysteresis <0.02%,

Model LPS-2KG, Scale Components Pty. Ltd., Australia). Force was sampled

at 100 Hz and the data fed into a personal computer (IBM compatible 486 DX)

and stored using a custom program written using AMLAB software

(Chatanooga, Inc., USA).

Weights equal to 40 and 70% of maximum isometric force were then

calculated using the following equation:

Weight = x * (y/100) - 74.6 kg

cos 41o / 9.81

where y is the percent required of the isometric maximum (equal to 40 or 70),

105

x is isometric maximum force in Newtons, cos 41o is used to calculate the

vertical component of the total isometric force, 9.81 (m.s-1) is a gravity

constant that is used to convert Newtons (N) to kilograms, and 74.6 kg is the

vertical component of the weight of the sled apparatus which forms part of the

total weight of the lifted system. The kilogram amount was then added to the

sled to the nearest five kilograms and maximal dynamic contractions

performed.

5.2.4 Test contractions

Subjects performed two maximal, dynamic contractions at both the 40% and

70% loads (i.e. two one-legged trials at both 40% and 70%, and two two-

legged at both 40% and 70%). The order of contractions was randomised

between subjects to minimise order effects. The weight was lowered in a

controlled eccentric phase lasting one to two seconds and then raised as

rapidly as possible. A spring mechanism prevented the sled from moving out

of the subject's reach at the top of the movement and allowed a safe, maximal

push to the limit of the subject's range of motion. Subjects were asked to hit

the spring at the top of the movement as hard as possible. All subjects were

allowed several familiarisation trials to gain confidence in the spring

mechanism prior to the recorded trials. Thus there was no deceleration of the

weight prior to hitting the spring. One minute of rest was allowed between

trials of a lift and five minutes of rest was allowed between different types of

lift. During dynamic trials, the force transducer again recorded force.

5.2.5 Data analysis

Reliability statistics including the difference in the mean force between the two

trials and the intra-class correlation coefficients were calculated by the

methods of Hopkins (2000). 95% confidence intervals (CI) were also

calculated to show the variation in reliability statistics. Finally, the bilateral

106

deficit was calculated similarly to that proposed by Howard & Enoka (1991)

except that instead of forces produced in left leg and right leg trials being

added and compared to the bilateral condition, the force produced in the

single leg condition was doubled. This would cause slight overestimation of

the bilateral deficit since often one leg is stronger than the other is and, in

general, subjects would have performed the trials with their strongest leg.

5.3 RESULTS

Mean (± SD) force production for the four conditions is presented in Table 5.1.

More force was produced during trials at the 70% load than at 40%.

Furthermore, more force was produced during bilateral trials. Interestingly,

force produced in the bilateral trials was less than double the force produced

during the unilateral trials. The subjects therefore exhibited a bilateral deficit

(-26.9% at 40% load, -28.2% at 70% load).

Testing

occasion

Trial Mean Force (N) SD (N)

First session 1L 40% 1176 2731L 70% 1721 2332L 40% 1706 2172L 70% 2540 379

Second session 1L 40% 1156 1481L 70% 1776 2892L 40% 1704 2432L 70% 2481 356

Results of the reliability tests are presented in Table 5.2. Intra-class

correlation coefficients were higher for trials at the 70% load than 40%. The

variability of the coefficients (indicated by the 95% CI) was also less for the

70% load. Therefore, reliability of trials at the heavier load was greater than

Table 5.1. Mean (±SD) force produced during each trial. More forcewas produced in trials at the 70% load and during bilateral trials.

1L – one-legged (unilateral), 2L – two-legged (bilateral)40% - 40% of isometric maximum added to machine70% - 70% of isometric maximum added to machine

107

for the lighter load. There appeared to be no effect of laterality on task

reliability.

Trial ICC 95% CI Change inMean (N)

95% CI

1L 40% 0.70 0.13 – 0.92 33.6 32.5 – 99.71L 70% 0.90 0.66 – 0.97 55.8 -222.0 – 133.62L 40% 0.64 0.06 – 0.89 70.7 -75.9 – 217.42L 70% 0.95 0.72 – 0.99 -17.1 -119.7 – 85.5

5.4 DISCUSSION

The purpose of the present study was to examine the reliability of test

performances in the dynamic forward hack squat task. The forward hack

squat was chosen as the test exercise since no reliability studies have been

performed for dynamic contractions and, given its novelty, subjects would be

unlikely to be accustomed to its movement pattern. As an adjunct, reliability

was measured with two different loads placed on the machine to determine

whether the load lifted (or the velocity of the movement) affected the test’s

reliability. Results of the reliability tests suggest that there was no difference

in the reliability of unilateral and bilateral tests. The result is interesting given

that unilateral strength tasks are less commonly performed and balance

during unilateral tasks may be more difficult to maintain. One could consider

that complex motor tasks that are performed unilaterally would be more

difficult to learn than bilateral tasks. However the results of the present study

suggest that subjects were equally able to perform uni- and bilateral tasks

reliably.

Of interest was the finding that the reliability of tasks at the heavier (70%) load

was higher than tasks at the lighter (40%) load. The result suggests that

Table 5.2. Reliability statistics for force produced during dynamicforward hack squat trials. Reliability was greater for the heavier loadswith no difference between uni- and bilateral trials.

1L – one-legged (unilateral), 2L – two-legged (bilateral)40% - 40% of isometric maximum added to machine70% - 70% of isometric maximum added to machine

108

something related to either the load lifted, or velocity of the movement,

affected reliability. The most likely explanation for this result is that the

greater load promotes greater kinaesthetic feedback from muscle, tendon and

joint proprioceptors. Particularly, muscle spindles, golgi tendon organs and

pacinian corpuscles could provide more feedback under the heavier loads.

Stretch or pressure stimulates proprioceptors. The greater the stretch or

pressure, the greater the feedback from these receptors. This information is

then received by the spinocerebellum which compares the information to the

signals sent from the cortical motor area (Sherwood, 1993). The

spinocerebellum then corrects deviations from the intended movement. Thus,

greater loads would allow more information from proprioceptors for the

spinocerebellum to correct movement.

Of final note is the result that the force produced during bilateral trials was

less than twice that produced in the unilateral trials. Thus the subjects in the

present study exhibited a bilateral deficit as has been reported in previous

studies (Häkkinen et al., 1996; Howard & Enoka, 1991; Tanaguchi, 1997).

The bilateral deficit was calculated similarly to that proposed by Howard &

Enoka (1991) except that instead of forces produced in left leg and right leg

trials being added and compared to the bilateral condition, the force produced

in the single leg condition was doubled. This would cause slight

overestimation of the bilateral deficit since often one leg is stronger than the

other is and, in general, subjects would have performed the trials with their

strongest leg. Nonetheless, the result provides further evidence that unilateral

and bilateral tests measure different entities and that testing should be

specific with respect to laterality. For example, strength tests measuring

changes in performance after unilateral training should be performed

unilaterally. This is especially true in light of the findings of the present study

that suggest the reliability of complex, unilateral tasks is as high as bilateral

tasks.

109

CCHHAAPPTTEERR 66:: SSTTUUDDYY FFOOUURR

110

PERFORMANCE RELATIONSHIPS

BETWEEN VERTICAL JUMP, SPRINT RUNNING

AND STRENGTH TRAINING EXERCISES:

IMPLICATIONS FOR MOVEMENT SPECIFICITY

6.1 INTRODUCTION

Based on the results of Study One it was concluded that the timing and

magnitude of hip, knee and ankle joint angle changes were similar for JSQ

and VJ (with arms crossed over the chest) tasks and for the FHS and the

acceleration phase of a sprint run. However, it is unclear whether subjects

who perform well in a JSQ or FHS test would also perform well in a VJ or

sprint run. The results of longitudinal studies indicate that adaptations to an

exercise stimulus are specific to the movement patterns of the training

exercises (Lindh, 1979; Martin et al., 1994; Rutherford et al., 1986; Thépaut-

Mathieu et al., 1988; Weir et al., 1994), even when the movement velocity of

the training exercise differs from the test exercise (Wilson et al., 1996; Young

& Bilby, 1993). As such, a subject could be expected to perform equally well

relative to other subjects in tests that require the same movement patterns,

even if the movement velocities of the tasks were dissimilar.

This creates somewhat of a paradox since the velocity specificity of

movement has also been extensively shown (Blazevich & Jenkins, 1997;

Caiozzo et al., 1981; Ewing et al., 1990). It is therefore unclear whether

adaptations to exercise are specific to the velocity of the training exercises, or

to some other closely related principle. It is possible that adaptations are

specific to the neuromuscular intent of the task rather than movement velocity

per se (Behm & Sale, 1993a). In the present thesis, the phrase

‘neuromuscular intent’ describes the ‘intended’ mode/s of muscular action.

111

That is, it describes the intention to provide concentric, eccentric or

isometric muscle contractions regardless of whether the muscles actually

lengthen or shorten and the actual mode and velocity of movement is not

considered. For example, the ‘neuromuscular intent’ during a VJ is to produce

high static muscle force, or to provide muscle stiffness in the squatting

position (transition between downward and upward phases), and then to

contract rapidly during the upward phase. Regardless, the entire movement

is regarded as high-velocity.

Examples of research indicating that neuromuscular intent, rather than

movement velocity, is an important factor in the adaptive process to

resistance training are limited. Adams et al. (1992) showed that a

combination of squat and plyometric training was superior to using only one

form of training to improve VJ performance. One could speculate that squat

training improved subject’s muscle strength and stiffness, while plyometric

training improved subject’s intermuscular coordination (Bobbert & Van Soest,

1994), use of the stretch-shorten cycle and high-velocity force production.

Therefore, training was optimum when exercises were specific to both

movement pattern and mode (neuromuscular intent). Further, Behm and

Sale (1993a) hypothesised that the ‘intent’ to perform rapid contractions was

important for velocity-specific adaptations to occur. Thus, while movement

pattern specificity is seen even with tasks of different velocities, the

neuromuscular intent of exercises might be important.

The purpose of this study therefore was to investigate the relationship

between subjects’ performances in JSQ and VJ tests, and the FHS and 20 m

sprint tests, to determine the extent to which subjectss performances in

certain tests were dependent on similarities in the movement pattern,

movement velocity and/or neuromuscular intent of the tests. It was

hypothesised that if movement pattern solely determined task similarity,

subjects would perform equally well (relative to other subjects) in JSQ and VJ

tests, and FHS and sprint tests. If both the movement pattern and

112

neuromuscular intent were important then not only should subject

performances in dynamic FHS tests and sprint tests be similar but so should

subject performances in ISQ and VJ tests. The VJ requires high levels of

muscle force for optimum use of the stretch-shorten cycle prior to the upward,

concentric, phase (Asmussen & Bonde-Petersen, 1974; Gollhofer et al., 1992)

and would therefore largely require the same neuromuscular intent as an ISQ

performed in a squating position. Finally, if movement velocity was important,

better relationships might exist between JSQ, VJ and sprint than ISQ tests.

6.2 METHODS

6.2.1 Subjects

Thirty-one athletic subjects including 23 men and eight women volunteered

from the University population (age range = 18 - 26 yrs). All subjects were

currently participating in organised sport (minimum of club-level) and had a

minimum of six months of resistance training experience. Both male and

female subjects were included in the study on grounds of equity however all

subjects had to perform a 20 m sprint in under 4 s and produce at least 1800

N in an isometric squat (knee angle 90o). Subjects had no recent injury or

medical conditions that would impede maximal performance and all subjects

read and signed statements of informed consent prior to participation. The

project was approved by the Southern Cross University Human Research

Ethics Committee prior to the commencement of testing.

6.2.2 Procedure

Following a standardised warm-up including ten minutes of low-impact

aerobic activity involving walking, running, subjects performed SQ, FHS, VJ

and 20 m sprint tests. Two minutes rest was allowed between successive test

trials while ten minutes of rest was allowed between the performance of

113

different tests. The order of tests was randomised between subjects by

each of the first 24 subjects being given one of 24 possible testing orders.

The next seven subjects were randomly allocated a testing order such that no

more than two subjects had the same test order. Thus the influence of

fatigue/potentiation on performance was minimised.

6.2.2.1 20 m sprint

Subjects’ times to run 10 m and 20 m were recorded by infra-red electronic

timing lights (Swift Performance Equipment, Australia) while running on a

synthetic, indoor surface. All subjects performed four practice runs at

increasing speed starting at a 'fast jog' and culminating in a maximal run.

Each subject was then allowed three timed runs, although a fourth run was

allowed if subjects produced their best time on the third run. Each sprint was

started from a semi-squatting position with one foot placed in front of the other

to lower the body's centre of mass and permit a more optimum acceleration

than that gained from an upright start. However 'crouch' starts of the type

seen in competitive running were not permitted to prevent bias toward

experienced sprint runners. The toe of the front foot was placed 30 cm

behind a line that marked the start of the 20 m. In this way the subjects’

forward lean did not prematurely break the infra-red beam between the

starting gates and activate the electronic timing mechanism. Subjects had

performed eight sprint sessions over four weeks prior to testing to practice

acceleration technique and ensure optimum running performance.

Subjects started in their own time with no external command. Timing was

automatically started when the subject broke the beam between the first pair

of timing lights (at 0 m of the 20 m). All subjects wore standard jogging shoes

and no performance shoes (i.e. spiked shoes) were allowed. Subjects were

instructed to run maximally to pass through all of the timing gates in the

minimum time.

114

6.2.2.2 Vertical Jump

Force and displacement were recorded for three maximal, double-leg VJ’s

with the subject’s arms folded across their chests. All had performed eight VJ

training sessions over four weeks prior to testing to practice jump technique

and ensure reliable jump performance. A cable position transducer with a

plastic-hybrid precision potentiometer (Model PT9101, accuracy ±0.10% full

stroke, Celesco Transducer Products, Inc., USA) measured displacement.

The cable was connected to a belt tightly secured around the subject’s waist

(Figure 6.1).

Voltage from the position transducer was sampled at 100 Hz using a personal

computer (IBM compatible, 486 DX) and stored on disc. Subsequently,

displacement was calculated using a scaling factor by a custom program.

The data were then smoothed with a fourth-order, zero-lag Butterworth filter

with a cut-off frequency of 10 Hz. Force was recorded using a Kistler Force

Platform (Type 9287, Kistler Instrumenté, Switzerland). Force data were

sampled at 1000 Hz using a personal computer (IBM compatible 486DX).

From force and displacement data maximum force, displacement, velocity,

Cable to transducer (above, not shown).

Belt to which cable was secured.

Figure 6.1. Body position for VJ showingcable (to position transducer) and belt.

115

Figure 6.2. Position for isometric squat test. Hipangles were measured during a squat with a freebar. Knee angles were maintained at 90o.Subjects then descended to these angles duringthe free-weight squat lifts.

power, time to peak power, and rate of power development were calculated

on all jumps.

6.2.2.3 Squat lift

Subjects performed three squat lift tasks: an ISQ and JSQ’s at 30% and 60%

of isometric maximum. Results from Study Two showed that these loads

were equal to approximately 44% and 88% of dynamic 1-RM. First, subjects

were asked to squat with an unloaded bar to a 90o knee angle and their hip

angle was measured. They then squatted under a bar that was fixed and

immovable such that their hip and knee angles were the same as those

recorded during the unloaded squat. This position is shown in Figure 6.2.

Subjects were instructed to perform a maximal isometric squat against the bar

for three seconds during which time force was measured by a Kistler Force

Platform, sampled at 1000 Hz and stored on computer. The instruction was to

perform the squat ‘as hard as possible’ and the maximum force recorded was

taken as isometric squat strength.

The peak in force was converted from Newtons of force to kilograms of weight

by dividing by the gravity constant of 9.81 ms-2 and 30% and 60% of this load

116

calculated. Subjects then performed three squats (with a free bar) on the

force platform with these loads. The subjects were required to lower the

weight slowly to a 90o knee angle (practice repetitions allowed the subjects to

estimate this position and each trial was observed to ensure the knee angle

was very close to 90o at the bottom of the movement). The subject then

exerted maximum effort upward against the weighted bar which was lifted

rapidly such that subjects’ feet often left the ground. The squat could be best

described as a jump squat (JSQ). The maximum force recorded during the

concentric (upward) phase was taken as a measure of squat strength

(Schmidtbleicher & Buehrle, 1987). The same test was repeated for the 60%

load. Thus, force measures were obtained for the squat lift under isometric

conditions, and with two different dynamic loads. From the force data, peak

force and time to peak force were calculated.

6.2.2.4 Forward Hack Squat

Subjects performed three maximum efforts of a two-legged FHS. These

included a maximal IFHS and lifts at 40% and 70% of isometric maximum.

Results from Study Two showed that these loads were equal to approximately

36% and 62% of dynamic 1-RM. The subject placed two feet on the foot

platform such that the body formed a straight line from the head to the ankle

while in the standing position. The subjects then lowered the weight until the

internal hip angle was 90o and the internal knee angle was 110o (Figure 6.3).

This approximated the hip and knee angles during push-off in the acceleration

phase of sprint running (Jacobs & Ingen Schenau, 1992). A metal peg was

used to hold the machine in this position for subsequent maximal isometric

contractions. For these contractions, subjects lifted the sled slowly until the

metal peg stopped its upward movement and hip and knee angles were

checked to ensure they were at 90o and 110o respectively. Subjects then

provided a maximal isometric contraction (i.e. as hard as possible) while

maintaining the pre-determined hip and knee angles. The contractions lasted

three seconds. Force during each isometric contraction was sampled at 100

117

Figure 6.3. Position for the isometricforward hack squat (FHS). The hipangle (angle between the C7 vertebra,greater trochanter and lateral condyle)was 90o and knee angle 110o.

Hz by a load cell placed in series with the movement direction of the weighted

sled (Output = 1.9231 mV/V, hysteresis <0.02%, Model LPS-2KG, Scale

Components Pty. Ltd., Australia). The signal was collected using a personal

computer (IBM compatible 486 DX) and data stored using a custom program

written using AMLAB software (Chatanooga, Inc., USA; see Appendix X).

To determine weights equal to 40% and 70% of maximum isometric force, the

vertical component of the force was calculated first. The following equation

was used:

Weight = x * (y/100) - 74.6 kg

cos 41o / 9.81

where y was the percent required of the isometric maximum (equal to 40 or

70), x was the previously determined isometric maximum force in Newtons,

cos 41o was used to calculate the vertical component of the total isometric

force, 9.81 (m.s-2) is the gravity constant used to convert Newtons (N) to

kilograms, and 74.6 kg is the vertical component of the weight of the sled

apparatus which forms part of the total weight of the lifted system. That is, the

vertical component of the total force provided during the isometric contraction

was calculated, a percentage of that weight determined (40% or 70%) then

the weight of the sled was subtracted to determine the actual weight to be

added to the sled. The kilogram amount was then placed on the sled to the

nearest five kilograms.

118

Subsequently, the subject performed maximal, dynamic contractions at the

40% and 70% loads where the weight was lowered in a controlled eccentric

phase lasting one to two seconds and then raised as rapidly as possible. A

spring mechanism prevented the sled from moving out of the subject's reach

at the top of the movement and allowed a safe, maximal push to the limit of

the subject's range of motion. The subject was asked to hit the spring at the

top of the movement as hard as possible. All subjects were allowed several

familiarisation trials to gain confidence in the spring mechanism prior to the

recorded trials. Thus there was no deceleration of the weight prior to hitting

the spring. During dynamic trials, both force and displacement were

recorded. Displacement was measured by a cable position transducer (as

described previously) with the cable attached to the sled apparatus and data

was collected using an IBM compatible computer. From the force and

displacement recordings, maximum movement velocity, peak force and peak

power were calculated as measures of performance.

6.2.3 Data Analysis

After force and displacement data were collected during the SQ, FHS and VJ

tests, various performance variables were calculated, as mentioned above, by

a custom program. All variables were subject to Correlation and Components

Analysis (SPSS for Windows v10.0, SPSS Inc.). Numerous variables (related

to power, maximum movement velocity and time to peak force and power)

were highly inter-correlated and were listed under the same components in

the Component analysis. Such variables were eliminated from further

analysis since they provided no information in addition to that gained from

analysing displacement and force variables (from which they were calculated)

alone. As such, analysis of the results was limited to force measures for the

resistance tasks, as well as VJ height and sprint running time.

Pearson's product moment correlation coefficients were calculated to

119

determine relationships among the performance variables. Alpha level was

set at 0.01 to decrease the likelihood of Type I error. Thus only highly

significant relationships were reported as such. The various components

associated with subject performances were also analysed by Components

Analysis using Principal Components extraction and Varimax rotation (SPSS

for Windows v10.0, SPSS Inc.).

6.3 RESULTS

Descriptive statistics for the variables analysed are presented in Table 6.1.

Results of the correlation analysis are presented in Table 6.2. Two-legged

FHS performance was significantly correlated with 10 m and 20 m sprint time

(r = -0.54 – -0.73, r2 = 0.29 – 0.53; p<0.01) such that subjects who ran faster

also performed better in FHS tests. Force produced during the SQ was also

correlated with 10m and 20 sprint time although the correlations were

consistently, but only slightly, lower (r = -0.51 – -0.67, r2 = 0.26 – 0.45; p<0.01;

compare correlations in Table 6.2). Indeed coefficients of determination

suggest that the proportion of the sprint times that can be accounted for by

squat performance was less than 45%. Force produced during the FHS

(isometric, 30% and 60%) were also significantly related to VJ height (r = 0.53

Table 6.1. Mean performance (±SD) forthose variables selected for analysis.

Performance Variable Mean (±SD)10 m sprint time (s) 1.89 (0.22)20 m sprint time (s) 3.28 (0.40)VJ height (m) 0.42 (0.10)FHS isom. (N) 1824 (487)FHS force 40% (N) 1182 (473)FHS force 70% (N) 2004 (586)Squat force isom. (N) 1709 (305)Squat force 30% (N) 1915 (397)Squat force 60% (N) 2294 (586)isom. – isometric30%, 40%, 60%, 70% - load lifted aspercent of isometric maximum.FHS – forward hack squat test

120

– 0.71, r2 = 0.28 – 0.50; p<0.01) as was force produced during ISQ (r = 0.63,

r2 = 0.40; p<0.01) and squat with a load of 30% of isometric maximum (r =

0.55; r2 = 0.30; p<0.01). However force produced during a squat with 60% of

isometric maximum was not significantly correlated (Figure 6.4).

Table 6.2. Significant correlation coefficients (p<0.01) forperformance data.

Strength Variable 10 m time 20 m time Vertical jump

FHS isom. -0.72 -0.73 0.56

FHS force 40% -0.54 -0.56 0.58

FHS force 70% -0.72 -0.71 0.68

Squat isom. -0.67 -0.51 0.63

Squat force 30% -0.50 -0.61 0.55

Squat force 60% -0.61 -0.67 (0.44)

isom. – isometric30%, 40%, 60%, 70% - load lifted as percent of isometric maximum.FHS – forward hack squat testAll correlations (non-bracketed) are significant, p<0.01.Bracketed correlation coefficients were not statistically significant.

0500

10001500200025003000350040004500

0 0.2 0.4 0.6 0.8

Vertical Jump Height (m)

Squ

at F

orce

(N

)

Squat forceisom.

Squat force60%

Linear (Squatforce 60%)

Linear (Squatforce isom.)

Figure 6.4. Scatterplots of isometric force produced during a squat (Squat force isom.)and force during a squat with a load of 60% of maximum isometric load (Squat force 60%)against VJ height. There is a higher correlation between ISQ force and jump height (r =0.63) than squat force at 60% of isometric maximum and jump height (r = 0.44).

121

Results of the Components Analysis were that the variables could be

grouped according to four components (see Table 6.3). The components in

Table 6.3 have been ordered according to the movement velocities and loads

of the movements with Component 1 being the slowest movement velocity

and Component 2 the fastest. SQ and IFHS variables have not been grouped

with any of the high-speed movements suggesting that their force-velocity

characteristics were different. The results also show however that sprint time

was not grouped with any of the FHS variables despite subjects performing

well in the FHS also performing well in the sprint (i.e. they were highly

correlated).

Another interesting finding of the study was that there was a plateau in sprint

running performance at high strength levels. That is, sprint times did not

improve linearly with strength at the highest strength levels (Figure 6.5). This

would have reduced the correlation between FHS and sprint performances

and suggests that strength is not the most important factor in performance in

fast runners.

Table 6.3. Results of the Factor Analysis. The analysis has revealed four componentsthat could be related to the movement velocity (or load) of the test. Components arearranged according to their movement velocity (i.e. 1,3,4,2).

Component 1 3 4 2

Variables Squat isom.Squat force 30%Squat force 60%FHS isom.

FHS 70% FHS 40% 10 m time20 m timeVJ height

Movement velocity

Movementload

Very low

Very high

Low

High

Moderate

Moderate

High

Moderate83% of total variance can be explained by the four components.Minimum communality = 0.65.isom. – isometric force30%, 40%, 60%, 70% - load lifted as percent of isometric maximum.FHS – forward hack squat test

122

6.4 DISCUSSION

Correlations between dynamic squat (which could be considered jump squats

since subjects’ feet invariably left the ground during the ascending phase) and

VJ performance were generally poor with the highest correlation being

between the ISQ and VJ (r = 0.63; p<0.01). Results of the component

analysis indicate also that their force-velocity characteristics were different

(Table 6.3). Therefore, although the results of Study One were that subjects

adopted similar movement patterns during the performance of VJ and JSQ

exercises, they were not well related functionally (r = 0.55; r2 = 0.3). A likely

reason for this discrepancy would be the different movement velocities

achieved and load lifted during performance of the tasks. The VJ is

performed at a high velocity and utilises the stretch-shorten cycle whereas the

squat lift is performed slower and with heavier loads. Indeed the lightest

dynamic squat was performed with a load equal to 30% of isometric maximum

(approximately 44% of dynamic 1-RM; Study Two). These loads are far

greater than for the VJ and the movement velocities achieved were therefore

0

500

1000

1500

2000

2500

3000

2.5 3 3.5 4 4.5

20 m Sprint Time (s)

FH

S F

orce

(N

)FHS isom.

FHS force 40%

Figure 6.5. Scatterplots of isometric force produced during a forward hack squat (FHSisom.) and force during a FHS with a load of 40% of maximum isometric load (FHS force40%) against 20 m sprint time. There is a plateau in sprint times at around 2.7 s.

123

very different. Thus, movement pattern alone did not determine task

similarity.

There was however a significant correlation between ISQ force and VJ height

despite the contraction modes of the two tasks being different. The close

performance relationship might reflect the necessity for high muscle strength

(muscle stiffness) in the squatting position for performance of both tasks (i.e.

the intent to produce high muscle stiffness regardless of the actual mode of

contraction; neuromuscular intent). The countermovement jump relies largely

on the stretch-shorten cycle for power development (Gollhofer et al., 1992).

Pre-activation of muscles to attain high muscle forces has been shown to

enhance the storage and utilisation of elastic energy in stretch-shorten

movements (Asmussen & Bonde-Petersen, 1974; Gollhofer et al., 1992) thus

increasing their efficiency. Further, earlier activation of agonist muscles in a

movement allows more work to be done early in that movement (Bobbert et

al., 1996; Fukashiro et al., 1995; Voigt et al., 1995; Walshe et al., 1997;

Wilson et al., 1991). The ability to use the stretch-shorten cycle optimally in

vertical jumping is therefore contingent on being able to attain high levels of

muscle force/stiffness in the squatting position. Given the high correlation

between ISQ force and VJ height, it appears that task similarity depended on

both the movement pattern and intent to produce high muscle force/stiffness.

Correlations between isometric and dynamic FHS force and sprint running

time were generally high (r = 0.56 – 0.73; p<0.01). Therefore, subjects who

produced large forces in the FHS tests also performed well in the sprint test.

The plateau in 20 m sprint times at high FHS forces (Figure 6.4) would have

affected this correlation. Component analysis revealed that performances in

FHS and sprint tasks were described by different components. 10 m and 20

m sprint times were listed under component 2, generally representing high

velocity movements (see Table 6.3), whereas the dynamic FHS variables (i.e.

not the isometric variables) were listed under components 3 and 4, generally

representing moderate or slower-velocity movements. A conclusion that may

124

be drawn from this is that while the sprint and FHS tests could not be

considered identical (given their different movement velocities), the similarity

in their movement patterns and force-velocity requirements were not as

different as for the isometric and dynamic squat and sprint/vertical jump tasks.

Since the weights used in FHS relative to 1-RM (36% and 62%) were lower

than for the squat (44% and 88%), the result was somewhat expected. Given

the movement patterns are the same (see Study One) and subjects who

performed well in FHS tests also performed well in the sprint tests, it appears

that movement specificity is determined both by the movement pattern and

neuromuscular intent, but not the velocity, of the tasks.

The results of this study offer some insight to the complex functioning of the

neuromuscular system. From Study One it was concluded that the movement

patterns of the JSQ and FHS exercises were similar to the VJ and sprint

(acceleration phase) respectively. Movement pattern-specific adaptations to

training have been shown repeatedly (Martin et al., 1994; Rutherford & Jones,

1986; Thépaut-Mathieu et al., 1988; Weir et al., 1994; Wilson et al., 1996),

even when training and testing exercises were performed at different

contraction velocities (Wilson et al., 1996; Young & Bilby, 1993). The results

of such research suggest that subjects should perform well in tests with the

same movement patterns. One would therefore conclude that, to at least

some degree, subjects who performed well in one resistance exercise would

also perform well in its related performance task. However, in this study,

subjects who performed well in the JSQ tests did not necessarily perform to

the same relative level in the VJ test.

These results may have been due to the resistance and performance (VJ and

sprint) tasks having different force-velocity characteristics (different

neuromuscular intent). The squat tests possibly required high dynamic

muscle strength while performance in the VJ tests depended on the efficiency

of the stretch-shorten cycle. The ISQ and VJ tests may have been more

functionally similar because of the high muscle force/stiffness required for

125

their performance (same neuromuscular intent). The results of this study

also suggest that while there was some difference in the force-velocity

characteristics of the FHS and sprint tests, neuromuscular intent was the

same. Therefore, subjects were likely to produce comparable performances

in tasks that had similar movement patterns, and required similar

neuromuscular intent. The velocity of movement was not a major factor. The

next step toward understanding the effect of movement pattern, movement

velocity and neuromuscular intent on training adaptations is to perform

longitudinal research investigating adaptations to the different types of

training.

In summary, specificity of task performance in humans has previously been

shown to be related to the movement pattern of tasks even when the

velocities at which the tasks were performed were not the same (Wilson et al.,

1996; Young & Bilby, 1993). However, the results of this study suggest that

the neuromuscular intent of the tasks is also important. The results do not

indicate that the actual movement velocity of exercises is important since ISQ

force was well related to VJ performance. A longitudinal study would best test

the influence of movement pattern and neuromuscular intent on training

adaptations.

126

CCHHAAPPTTEERR 77 –– SSTTUUDDYY FFIIVVEE

127

NEUROMUSCULAR AND PERFORMANCE

ADAPTATIONS TO SHORT-TERM CONCURRENT

RESISTANCE AND SPRINT/JUMP TRAINING

7.1 INTRODUCTION

Adaptations to RT appear specific to the movement patterns (Abernethy &

Jürimäe, 1996; Kitai & Sale, 1989; Weir et al., 1994; Wilson et al., 1996) and

velocities (Caiozzo et al., 1981; Delecluse et al., 1995) of the exercises used

in training. In studies investigating the movement-specific adaptations to

training, much of the specific adaptations have been ascribed to changes in

muscle recruitment strategies (Kitai & Sale, 1989; Weir et al., 1994) or in the

length-force characteristics of sarcomeres (Herring et al., 1984; Koh, 1995;

Van Eijden & Raadsheer, 1992). Velocity-specific adaptations have been

ascribed mostly to increases in type-II myosin heavy chain isoforms within

sarcomeres (Adams et al., 1993; Andersen et al., 1994), increases in the total

size or number of type II muscle fibres (Jansson et al., 1990; Mannion et al.,

1993) or an increase in the recruitment of motor units during muscle

contraction (Behm & Sale, 1993b; Cannon & Cafarelli, 1987; Häkkinen et al.,

1985 a,b; Häkkinen & Komi, 1985, 1986). Thus, specific adaptations to RT

occur in many different parts of the neuromuscular system. Despite this, little

research has examined movement-specific changes in muscle architecture, or

examined both muscular and neural changes simultaneously. Furthermore

longitudinal studies investigating movement pattern-specific effects have been

fraught with limitations (this will be discussed later).

128

7.1.1 Muscle Architecture

Muscle architecture describes the size of a muscle in terms of the volume,

cross-sectional area or thickness, the angulation of its fibres relative to the

tendon [pennation) and the length of its fibres (measured as fascicle length)

after training. These factors have been shown to change with RT

(Henriksson-Larsén et al., 1992) however little research has investigated such

changes. With respect to muscle size, increases have been commonly

observed after periods of resistance-type training with much of this increase

being related to fibre size (Colliander & Tesch, 1990; Narici & Kayser, 1995;

Sale et al., 1992; Wang et al., 1993). Increases in muscle size in response to

training appear after several weeks (Moritani, 1993; Moritani & DeVries, 1979;

Narici et al., 1989) and certainly after changes have occurred at the

sarcomere (Heslinga et al., 1995; Williams, 1990) and in the nervous system

(DeVries, 1968; Narici et al., 1989; Sale, 1988). Since few changes have

been seen in the electromyogram of experienced weight trainers (Häkkinen et

al., 1987, 1991), increases in muscle size have been proposed as the major

determinant of muscle strength in well-trained athletes (Narici et al., 1989).

In addition to muscle size changes, changes in muscle pennation could affect

strength development. Increases in pennation possibly allow a greater

muscle mass to attach to a given area of tendon (Kawakami, 1993; Rutherford

& Jones, 1992). As such pennation should increase with the size of the

muscle. Research examining the relationship between muscle size and

pennation (Henriksson-Larsén et al., 1992; Kawakami et al., 1993, 1995;

Rutherford & Jones, 1992) has not conclusively shown whether the two

variables are (Kawakami et al., 1993, 1995; Rutherford & Jones, 1992 [cross-

sectional]) or are not (Henriksson-Larsén et al. 1992; Rutherford & Jones,

1992 [longitudinal]) related. Therefore it is still unclear whether pennation

changes occur in response to changes in muscle size.

Longer muscle fibres have been theoretically and experimentally shown to

129

contract at higher velocities than shorter fibres (Burkholder et al., 1994;

Sacks & Roy, 1982; Wickiewicz et al., 1984). Since fibres are grouped into

fascicles, and the spaces between fascicles are visible in vivo using

ultrasound and computer aided techniques, fibre length is commonly

estimated by measuring the length of these fascicles (Fukunaga et al., 1997;

Kawakami et al., 1998). However no research had examined the relationship

between fascicle (fibre) length and human movement performance until Abe

et al. (1999) showed that fascicle length was greater in sprinters than long

distance runners, and Kumagai et al. (2000) showed a significant relationship

between fascicle length and sprint performance in 100 m sprinters. Still no

research has investigated changes in fascicle length (fibre length) in

controlled training studies using concurrent resistance and task training.

Therefore it is unclear whether fascicle length is altered in response to RT, or

concurrent resistance and task training.

7.1.2 Longitudinal Research

While some longitudinal studies have investigated neuromuscular changes

accompanying training, the exact neuromuscular adaptations that result from

training, and the populations to which the results can be related, are still

unclear. First, subjects in most training studies are not well-trained and

adaptations within their neuromuscular system may well be different to trained

individuals (Häkkinen et al., 1987; Narici et al., 1989). Second, the subjects in

such training studies have generally trained using isokinetic (Ewing et al.,

1990; Mannion et al., 1994; Narici et al., 1989) or isotonic (Abernethy &

Jürimäe, 1996; Petersen et al., 1989; Sale et al., 1992; Wilson et al., 1993,

1996) training modes without also performing additional, task-specific,

practice. A paucity of research has examined the effect of training movement

pattern or velocity when subjects performed both resistance- and task training

concurrently (Delecluse et al., 1995; Tanaka et al., 1993; Voigt & Klausen,

1990). Research that has examined adaptations to concurrent training

suggests that RT performed at high velocities (Delecluse et al., 1995) may be

130

more beneficial than that at lower velocities (Tanaka et al., 1993; Voigt &

Klausen, 1990) even when the movement patterns of the resistance and task

training exercises are similar (Tanaka et al., 1993). Third, while much

research has focussed on changes in the nervous system with training,

relatively few studies have investigated changes in muscle architecture after

RT (Henriksson-Larsén et al., 1992; Kawakami et al., 1993, 1995; Rutherford

& Jones, 1992). Moreover, none have examined changes in both the nervous

system and muscle architecture after a period of concurrent resistance and

task training.

Given that, for most athletes, RT forms only part of a total training program, it

is important that adaptations to RT are described when task training is

performed concurrently. The purpose of the present study was first to

determine if changes in VJ, sprint run and strength tests were related to the

movement pattern or velocity of multi-joint, dynamic RT exercises in well-

trained subjects, and second to examine changes in the nervous and

muscular systems when the RT was performed concurrently with VJ and

sprint training (i.e. task practice).

7.2 METHODS

7.2.1 Subjects

Thirty active individuals from the University population volunteered for the

study (Age range = 18 – 26 yrs). Given the magnitudes of changes in

performance shown in studies investigating movement-specific adaptations,

an effect size of at least 1.0 was expected. A priori power analysis revealed

that ten subjects were required in each group to be 80% confident (i.e. power

= 0.8) of finding differences significant at the 0.05 level (Table 8.3.13, Cohen,

1988). Of the 30 subjects, 23 (eight women & 15 men) completed the study

with the largest portion of withdrawals resulting from injury sustained outside

131

the study. This would have affected the power of tests. Male and female

subjects have been used in many strength/sprint training studies (Esbjörnsson

Liljedahl et al., 1996; Herbert et al., 1998; Hortobàgyi et al., 2000; Mannion et

al., 1994; Smith & Rutherford, 1995). Given the difficulty in recruiting athletic

subjects for the present study, both men and women were included to

increase subject numbers. All subjects had participated in sport at the

recreational or representative level, had a minimum of three months of weight

training experience, could produce a force equal to twice their bodyweight

during an isometric squat lift, had no recent injuries or medical conditions that

would prevent maximal exertion. All subjects read and signed statements of

informed consent prior to participation in the study. The research was

approved by the Southern Cross University Human Ethics Committee

(Appendix B).

7.2.2 Protocol

Subjects participated in four weeks of resistance- and sprint/jump training

(familiarisation) prior to a second five-week (specific) training phase (Figure

7.1). During the four-week familiarisation phase, subjects performed two

sprint/jump sessions per week with each session involving one hour of

supervised training in sprint running and vertical jumping technique. The

purpose of such training was three-fold: 1) to ensure all subjects had

experience with sprint and jump technique so that ‘learning’ of the tasks was

minimal during the subsequent ‘specific’ training phase, 2) to improve the

reliability (decrease the variability) of the subjects’ performances, and 3) to

ensure subjects were training regularly prior to the first testing occasion.

In addition to the sprint/jump training, subjects also performed two supervised

weight training sessions per week. Each session involved performing three

sets of ten repetitions of reclined leg-press, deadlift, leg extension, leg curl

and standing calf raise exercises. If greater than 12 or less than eight

repetitions were performed in a set, the weight was adjusted for subsequent

132

sets. The purpose of such training was to ensure all subjects were performing

weight training consistently prior to the study and that all subjects were

competent lifters. Attendance at training sessions was monitored and

subjects who did not perform a minimum of six sprint/jump and six RT

sessions over the four-week period were excluded from the study. Given that

all subjects had been performing RT, and training involving sprinting and

jumping, prior to the study those subjects recruited for the specific training

phase could be considered well-trained.

Following the four-week familiarisation phase, subjects were divided into three

training groups with male and female subjects distributed equally among the

groups. These groups were named squat (SQ), forward hack squat (FHS)

and sprint/jump (SJ) based on their training (see over). Briefly, all groups

performed at least two sprint/jump sessions per week with SQ and FHS also

performing two weight training sessions and SJ two additional sprint/jump

sessions (i.e. four sessions) each week. By the end of the study the SQ, FHS

and SJ groups contained eight, seven and eight subjects respectively (each

group contained at least two females, thus male/female ratios were similar

between the groups).

After the four-week familiarisation phase, but before the five-week specific

training phase, subjects performed 20 m sprint, vertical jump, squat lift,

forward hack squat and isokinetic leg extension tests (pre-test). On a

separate day, EMG was collected from leg musculature during performance of

vertical jump and sprint tasks. Collecting EMG on a separate day would have

minimised the effects of fatigue on the EMG recordings. Muscle thickness,

Familiarisation

(4 weeks)

Pre-test Specific training (5 weeks)

Four groups: SQ, FHS & SJ

Post-test

Figure 7.1. Overview of training and testing. A familiarisation phase preceded the 5-week ‘specific’ training phase to ensure all subjects were currently training. Testingwas performed before and after the specific training phase.

133

pennation and fascicle length were also measured at two regions of both

the vastus lateralis and rectus femoris muscles (see over). The tests were

repeated after the five-week specific training phase (post-test). Three days of

rest separated the last training session of each phase from the testing.

7.2.3 Testing

7.2.3.1 20 m sprint

Times to sprint 10 m and 20 m were recorded using the same protocol

described previously (see Study Four). Briefly, subjects performed three

maximal sprints from a standing start. Electronic timing gates at 0, 10 and 20

m recorded time. The best running time to the 10 m and 20 m marks were

taken as that subject’s performances.

7.2.3.2 Vertical Jump

Subjects performed single- and double-leg vertical jumps using the same

protocol as described previously (see Study Four). Briefly, subjects

performed countermovement jumps with arms crossed over the chest. Jump

height was measured by a cable position transducer; the cable was

connected to a belt secured around the subject’s waist. The greatest jump

height recorded in three trials for both one- (subject’s preferred leg) and two-

legged jumps was taken as a measure of jump performance.

7.2.3.3 Squat lift

Subjects performed dynamic, free-weight squat lifts (minimum internal knee

angle was 90o) and isometric squats as described previously (see Study

Four). The descending phase of the squat lift was performed at a moderate

speed (1-2 s) but the ascending phase was performed maximally. In most

134

instances the subject’s feet left the force platform at the end of the

movement and is best termed a ‘jump squat’ (JSQ). The maximum force

produced during the squat lift was taken as a measure of performance.

Testing maximum isometric strength rather than 1-RM strength would have

improved subject safety while allowing good measurement of subjects’ task-

specific strength. Testing of the relationship between dynamic and isometric

squat maximums suggested that weights of 30% and 60% of isometric

maximum correspond to weights of 44% and 88% of dynamic maximum (see

Study Two). Thus force produced during these efforts may indicate the

subjects’ ability to lift lighter and heavier loads rapidly.

7.2.3.4 Forward hack squat

Subjects performed both isometric and dynamic single- and double-leg FHS

as described previously (see Study Four). For the dynamic FHS, subjects

lowered the sled (including weights) at a moderate speed (1-2 s downward

phase) but performed the concentric phase at maximum velocity. A metal

stop was placed such that a spring attached to the sled contacted the stop at

the top of the movement, but before the subjects’ feet left the foot platform.

Therefore, subjects could provide maximum force throughout the concentric

phase without concern for injury. The maximum force produced during FHS

lifts (disregarding the force produced during impact of the sled with the metal

stop) was taken as a measure of performance. The minimum internal hip

angle was 90o and the internal knee angle was 110o. This approximated the

hip and knee angles during push-off in the acceleration phase of sprint

running (Jacobs & Ingen Schenau, 1992). Testing of the relationship between

dynamic and isometric forward hack squat maximums suggested that weights

of 40% and 70% of isometric maximum correspond to weights of 35% and

62% of dynamic maximum (see Study Two).

135

7.2.3.5 Isokinetic knee extensor torque

Concentric, isokinetic knee extensor torque of each subject’s right leg was

tested at joint angular velocities of 30o.s-1 and 180o.s-1 using a KinCom

Isokinetic Dynamometer (Chatanooga Inc., USA). Subjects sat with a hip

angle of 90o and were secured by straps across the chest and waist. Gravity

correction of the subject’s limb was performed and anatomical references

defined. To define the anatomical reference, joint angle was measured during

a maximal knee extension contraction and this angle entered into the

computer. Often, angles are defined under passive conditions and the joint

angle during contraction can be different to that measured by the

dynamometer. In our case, the joint angle measured by the dynamometer

was very close to the joint angle actually achieved during the maximal

contractions. During testing, subjects performed two sets of four repetitions of

isokinetic knee extension and flexion at an angular velocity of 180o.s-1, then

three maximal repetitions of knee extension and flexion at 30o.s-1.

Only force data collected during knee extension was used for analysis. From

this, the maximum torque produced at both speeds was calculated, as was

the angle at which the maximum torque was produced at 30o.s-1. The angle of

maximum torque at 180o.s-1 was not used for analysis since torque at this

speed was highly variable both within and between subjects. The knee joint

angle during the concentric movement phase ranged from an external angle

of 95o (knee flexed) to 10o (knee extended) however only data collected from

knee extension between the angles of 80o and 20o was used for analysis. As

such, torque peaks associated with the impact of the tibia against the force

transducer early in the concentric phase were not included in the analysis.

7.2.3.6 Muscle Size and Architecture

While in a supine position subject’s knees were flexed to 90o and supported

136

by the researcher. After applying hypoallergenic, water-soluble

transmission gel to the skin, a qualified sonographer used an 8 MHz linear

ultrasound transducer (Acuson 8L5, California, USA) to scan the surface of

the thigh to locate the muscle-tendon junction at the distal end of the rectus

femoris muscle (RF d). The point was clearly identified since the muscle

appears dark, but the tendon light, on the computer screen (see Figure 7.2).

The areas of transition from muscle to tendon appeared small (approximately

one centimetre). The transducer was then moved two centimetres proximally

where muscle thickness (distance between the superficial and deep borders

of the muscle) was calculated from a transverse section by an Acuson

Sequoia 512 system (Acuson, California, USA) after the muscle was manually

traced on the image screen. The distance to this point was measured on a

line from the joint cleft at the lateral condyle of the femur to the palpable

centre of the greater trochanter (Figure 7.3). The scanning head was then

rotated to view a longitudinal section of the muscle where the aponeurosis of

the muscle and fascicles attached to it were clearly visible. A photograph

(computer-aided transparency) of the ultrasound image was taken for

subsequent pennation measurement. The scanning head was then moved

proximally and muscle thickness measured at regular intervals along the

Figure 7.2. The muscle-tendon junction of rectus femoris was determined by moving thescanning head (ultrasound) distally along the thigh. Diagram A shows the dark centre of rectusfemoris and the white connective tissue that surrounds it (circled). The muscle-tendon junctionwas defined as the point at which the whole of the muscle became white. A longitudinal section(Diagram B) where the rectus femoris can been seen to taper from dark muscle to whiteconnective tissue can verify this.

A B

Rectus femoristapers

137

muscle. At a point where the muscle thickness was deemed greatest, the

measures were repeated. This point was named RF p (proximal rectus

femoris). Measures of muscle thickness and pennation after the five weeks of

training were taken as close as possible to these sights after measuring the

distances from the lateral condyle. Repeatability of the measures was

practiced prior to testing to ensure reliability and has been demonstrated

previously (Giorgi et al., 1999). The reliability of the sonographer has been

determined previously (Ostrowski et al., 1997).

For the vastus lateralis muscle, measures were taken with the subject

remaining in a supine position with the knee flexed to 90o. Measures of

muscle thickness and photographs for pennation assessment were taken two

centimetres from the most distal muscle point (VL d – distal vastus lateralis)

and at the point of greatest muscle thickness (VL p – proximal vastus

lateralis). Again, the distances to these points were measured from the lateral

condyle.

Figure 7.3. Muscle thickness, pennationand fascicle length estimates weremade at two sites of the rectus femorisand vastus lateralis muscle usingultrasound. These sites are shown inthe diagram and described in the text.

RF – Rectus femorisVL – Vastus lateralis

138

Pennation measurement

The angles of three fascicles were measured manually three times on the

photograph transparency of the ultrasound image by a goniometer and the

angle for each fascicle taken as the median of the three recordings. The

fascicle angle was measured at the fascicle-aponeurosis junction. As such

slight fascicle curvature was not accounted for (Kawakami et al., 1993). The

mean of the median angle of the three fibre bundles was considered the

muscle pennation angle. The bundles chosen were contained within two

centimetres of each other in the muscle. Reliability of pennation

measurement has been shown (Kawakami et al., 1993; Henriksson-Larsen et

al., 1992) and reliability of our pennation measurements has also been shown

(Blazevich & Giorgi, 2001).

Estimation of fascicle length

Fascicle length (FL) at each region on the two muscles was estimated as the

length of the hypotenuse of a triangle with an angle equal to the pennation

angle (θ) and the side opposite to this angle equal to the muscle thickness (T).

Therefore, FL=T/sinθ. Fascicle length is commonly estimated by this method

(Henriksson-Larsén et al., 1992; Kawakami et al., 1995; Kumagai et al.,

2000). Nonetheless, more recently digital measures have been used where

the fascicle length is measured after tracing it from ultrasound photographs.

We have compared the two methods, the results are presented in Appendix

F). Briefly, mathematical estimation is less reliable than the digital method

making significant changes in fascicle length harder to detect. Given the

results in Appendix F, we predict an error of up to five millimetres may be

expected in the present study using the mathematical method. Digital

techniques were not available for use in this study.

139

5.2.3.7 Electromyographic (EMG) analysis

EMG recordings of five muscles of the right leg (gluteus maximus, biceps

femoris [long head], psoas major, rectus femoris and vastus lateralis) were

analysed for contraction/co-contraction patterns after subjects performed both

two-legged vertical jumps and sprint runs. After hair removal and light

abrasion with sandpaper to decrease skin resistance, stainless steel, bipolar,

pre-amplified surface electrodes (inter-electrode distance = 20 mm) were

placed over the muscle belly’s of the five muscles (see Table 7.1). The

recording electrodes were oriented parallel to the predicted line of muscle

fibres. The leads from the electrodes were attached to 6 m extension leads to

allow the subjects to move over a 12 m distance. Subjects then performed

two maximal vertical jumps and two maximal sprints over 8 m such that the

right leg contacted the ground on at least three occasions. A video camera

operating at 50 Hz (shutter speed 1/1000 s) captured the movement on tape

and EMG data collection commenced immediately as the subjects were

instructed to perform the jump or sprint. A light-emitting diode placed in the

camera’s view was illuminated at the same time so the EMG could be

synchronised to the movement. During the movements, raw EMG signals

sampled at 1000 Hz were amplified and collected using A/D conversion

(DT01EZ; Data Translation, USA) by personal computer (386 DX IBM-

compatible). High frequency noise was reduced by a 500 Hz anti-alias filter

and low frequency noise (particularly that caused by movements of the long

electrode cables) was minimised by passing the raw signals through a 10 Hz

high-pass filter. The data was then stored for subsequent analysis.

The VJ was analysed as two parts, the first being the descending or eccentric

phase and the second being the ascending or concentric phase. The sprint

run was likewise divided into two parts, the first being from first contact of the

foot with the ground (foot-ground contact; right foot) to the first contact of the

contralateral (left) foot with the ground, and the second being from

contralateral foot-ground contact to foot-ground contact of the first (right) foot.

140

For all subjects, the stride analysis started from the first contact of the right

foot after the subjects had left the starting position. To determine the sections

of EMG used for analysis, the video was analysed for event times. The

associated EMG was then rectified and then averaged in bins of 5% of

movement time. The two phases of each movement were analysed

separately so that the first 50% of the EMG output related to the first

movement phase while the second 50% related to the second movement

phase. Thus, the different phases of the movements were time-normalised.

The EMG data were analysed by two methods. First, EMG recorded during

each 5% period were normalised to the greatest EMG recorded in any 5% bin

for a particular muscle in that movement. Thus an indication of the magnitude

of EMG detected during the movements was obtained. Second, muscle co-

contraction patterns were calculated for the sprint run and muscle activity

onset times calculated for the VJ. A ten-point moving average (1% of

movement time) was applied to the rectified data before determining muscle

burst onset (on) and offset (off) times. Each muscle was analysed separately

and deemed ‘on’ when ten consecutive samples of EMG exceeded a

threshold of 15% of the maximum amplitude of EMG collected for the duration

Table 7.1. Details of electrode placements on the five thigh muscles.

Muscle Electrode placement

Gluteus maximus (GL) Centre of the palpable part of the muscle with the electrodealigned diagonally downwards in line with the fibres

Biceps femoris (BF) A point 50% of the distance from the gluteal fold to the poplitealcrease on a line drawn vertically up the thigh from the palpabletendon on the lateral aspect of the lower, posterior thigh.Subjects flexed the knee to cause contraction of the muscle toensure electrode placement on the belly of the muscle. Theelectrode was aligned parallel to the femur.

Vastus lateralis (VL) A point 50% of the distance from the lateral border of the patellato the greater trochanter and on the line joining these landmarks.The electrode was aligned such that the long axis of the electrodeconfiguration passed through the patella’s centre.

Rectus femoris (RF) A point 50% of the distance from the most medial palpable pointof the inferior superior iliac spine to the middle of the superiorborder of the patella and aligned parallel to the femur (thus thecomplex pennation of RF was not accounted for).

Psoas major (HF; hipflexor

Immediately below the inguinal fold and 2 cm medial to theanterior superior iliac spine. Aligned parallel to the femur.

141

of the task. A 15% threshold was selected after trialing thresholds ranging

from 5% to 30% and comparing the on and off times derived manually. The

muscle was deemed ‘off’ when the EMG amplitude diminished to less than

15% of the maximum normalised EMG for ten consecutive samples. On and

off times were checked manually after analysis to reduce the risk of identifying

the muscle as ‘on’ when the muscle was relatively inactive (type I error). This

method of determineing on/off times has been previously presented (Steele &

Brown, 1999).

Muscle co-contraction changes (sprint run) for two pairs of muscles (GL/HF

and VL/BF) were evaluated. The analysis was run for three separate data

sets. First, the percent of movement time in which both muscles were active

in the first and second phases of the movements (i.e. foot-ground contact and

recovery phases for running, and descending and ascending phases of the

vertical jump) was calculated. Two further data sets were calculated, one

where co-contraction patterns were normalised to the average time in which

the muscles were labeled ‘on’ (average of percent time in which one muscle

was ‘on’ and the percent time the second muscle was ‘on’), and a second

where co-contraction patterns were normalised to the ‘on’ time of the muscle

that was active longest during the movement.

Specific terms have been used to describe certain phases of the sprint

running movement. These include:

Acceleration phase of the sprint run – Considered as that part of a sprint run

beginning at the movement’s onset and ending when maximal (or near-

maximal) speed is reached. In the present study, the term refers more to the

early part of this phase when the body has a distinct forward lean. Jacobs &

Ingen Schenau (1992) described this phase by examining sprint runners from

the second to the fourth step of a sprint run from a stationary start.

Foot-ground contact phase – occurs when the foot first strikes the ground and

142

ends when the foot leaves the ground.

Recovery phase – describes that part of the running stride from when the foot

leaves the ground to when the foot once again makes contact with the

ground.

Toe-off – refers to the precise moment when the foot leaves the ground (ie

between foot-ground contact and recovery phases).

7.2.4 Training

7.2.4.1 Training groups

Squat (SQ) training

Subjects in the squat (SQ) group used the free-weight squat lift as their

dominant training exercise during the specific training phase (supplemenatry

exercises are described later). The squat lift required subjects to lower their

body to a sitting or squatting position with a knee angle of 90o with a weighted

bar rested across the shoulders then lift the weight back up to the starting

position. Subjects were guided to the correct knee angle by a supervisor

during each squat. Training was performed two times per week. In the first

session of each week (heavy day), subjects performed three warm up sets of

the squat lift (see Appendix D for details) followed by three sets of six squats

with weights equal to 50% - 80% of their pre-determined isometric maximum

force (described earlier). Three minutes rest separated sets. Weights were

increased when subjects could perform more than six repetitions in a set. The

weight lifted throughout the five weeks of training increased from 50 – 60% to

70% - 80%. In some instances, subjects lifted up to 90% of their

143

predetermined isometric maximum in sessions toward the end of the

training period. In the second session of each week (light day), subjects lifted

weights equal to 30 – 50% of their isometric maximum for three sets of six

repetitions. No subjects were allowed to lift more than 50% of their

predetermined isometric maximum regardless of strength gains. In both

sessions, the ascending (concentric) phase of the squat was performed at

maximum velocity such that the subjects’ feet left the ground. Thus, the squat

could be considered a jump-squat. The loads were different between

sessions to provide a different movement stimulus (Wilson et al., 1993) and

prevent subjects becoming accustomed to the training. Typical training

sessions for heavy and light days are presented in Appendix D.

In addition to the squat lift training, SQ subjects also performed two sets of ten

repetitions of a back extension exercise, three sets of eight repetitions of a leg

curl (knee flexion) and two sets of eight standing calf raises. All sets were

performed with a weight that allowed movement failure within the allotted

number of repetitions on the heavy day, but could be performed with greater

movement speed and without failure on the light day. Subjects were also

encouraged to perform two sets of abdominal crunches and spend 15 minutes

stretching the major lower limb muscles after training. In addition to the

weight training, SQ subjects also performed two sprint/jump sessions per

week (see over).

Forward hack squat (FHS) training

Training performed by the forward hack squat (FHS) group differed to SQ only

in the exercise used as the dominant lift in weight training. FHS used the one-

legged FHS exercise as their dominant training exercise during the specific

training phase (Figure 7.4). Thus, in contrast to SQ, training was performed

unilaterally since sprint running is performed unilaterally and some research

(Häkkinen et al., 1996; Rube & Secher, 1990; Tanaguchi, 1997) has shown

that adaptations to RT can be specific to the laterality of training exercises.

144

Within each session, legs were trained alternately with one set being

performed with the right leg and the next with the left. Training was performed

twice a week (same as SQ). In both sessions, the concentric (upward) phase

of the FHS was performed at maximum velocity such that the sled on which

the weights were placed was moved forcefully into a spring at the top of the

movement. The spring height was set individually for each subject. Typical

training sessions for heavy and light days are presented in Appendix D.

Sprint/jump (SJ) training

Subjects in the sprint/jump (SJ) group did not perform weight training during

the five-week specific training phase. Instead, SJ subjects participated in four

sprint/jump sessions. Thus, the total number of training sessions performed

by all training groups was the same.

7.2.4.2 Sprint and jump training

SQ and FHS subjects performed two sprint/jump training sessions per week

while the sprint/jump (SJ) group performed four sessions per week. The

Figure 7.4. Single-leg forward hack squat. These diagrams show clearly the body position andlaterality of the task. The ‘free’ leg can also be seen flexing while the ‘working’ leg extends.This movement was performed in an attempt to better simulate the acceleration phase of sprintrunning.

145

sessions typically lasted one hour and consisted of a ten minute warm-up,

five minutes stretching, 35 min of sprint and jump training and another ten

minutes of stretching at the end of the session. The sprint/jump sessions

were divided into a sprint component and jump component. During the sprint

component, subjects predominantly practiced running over distances up to 30

m using the techniques previously taught to them. A qualified sprint coach

who was unaware as to the group allocation of subjects supervised all

sessions for each group. Subjects often ran up to 20 sprints in a session with

training volume increasing over the nine weeks of training (four-week

familiarisation and five-week specific training phases). The jump component

typically consisted of both one- and two-legged jumps in sets of three to five

repetitions. Subjects practiced jumping with different countermovement

distances in order to find their optimum knee bend. Subjects were also

expected to perform the jumps maximally and ensure complete extension of

the hip, knee and ankle joints at take-off.

Sessions typically consisted of 20 jumps separated by rest. The training load

was increased over the nine weeks of training. The intensity of the runs and

jumps was always maximal, however the volume of work increased. In the

first week of training, two sets of three sprint runs were separated by two

minutes of rest. Two sets of three vertical jumps were also performed with

one minute of rest separating sets. By the end of the study, four sets of four

sprints with two minutes rest were performed with four sets of four vertical

jumps. For SJ subjects, sprint sessions could not be performed on four

consecutive days. Sprint training may, for example, be performed on

Monday, Tuesday, Thursday and Saturday. For SQ and FHS subjects sprint

sessions were performed on different days to the RT and one rest day

separated the four sessions. For example, sprint sessions may have been

performed on Monday and Thursday with RT sessions being performed on

Tuesday and Friday.

146

7.2.5 Data analysis

After satisfying the assumptions of homogeneity of variance (Lavene’s test),

sphericity (Mauchly’s test) and normal distribution of data (Kolmogorov-

Smirnov test), performance changes with training (sprint run, VJ, SQ and

FHS) were analysed using Repeated Measures ANOVA (SPSS v10.0, SPSS

Inc) with ‘group’ as the between subjects factor and ‘time’ (pre- to post-

training) as the within subjects factor. When significant group effects were

revealed, Tukey’s HSD post-hoc analysis was used to determine differences

between the three groups. For all analyses, significance was set at an alpha

level of p<0.05, unless otherwise stated.

Analyses of muscle thickness, pennation and fascicle length were performed

separately. For each measurement site, Repeated Measures ANOVA

examined significant effects of group and time. Interaction effects were

further analysed by one-way ANOVA of difference scores (ie. pre- to post-

training changes). Bonferroni post-hoc analysis tested for significant

differences. In the event of non-homogeneous distribution of data,

Tamhane’s T2 post-hoc analysis was used. Tamhane’s T2 post-hoc analysis

does not assume equal variances. To examine the relationships between

muscle thickness, pennation and fascicle length at each site on the muscles,

Pearson’s Product Moment correlation coefficients were computed on the

difference scores (absolute variable changes from pre- to post-training). In

order to control for type 1 error, significance was set at p<0.01.

Changes in isokinetic knee extension torque produced during contractions at

two speeds were compared using Repeated Measures ANOVA with ‘training

group’ as a between-group factor. Differences in the torque produced at the

different speeds, and changes in the angle at which peak torque was

produced were analysed. Between group effects were further analysed by

Tukey’s HSD post-hoc test.

147

Electromyogram data were analysed in two ways. First, changes (±95%

confidence intervals) in normalised EMG for each muscle were calculated for

each 5% of movement. Paired t-tests with Bonferroni correction were used to

assess differences between groups. Due to loss of data, only ten subjects

were included in the analysis. Four subjects had performed RT (SQ and FHS

subjects) while six performed only sprint and jump training (SJ subjects). As

such, comparisons were made only between weight-trainers and SJ subjects.

No comparison was made between SQ and FHS groups because the low

subject number and large number of t-tests performed would have made

significant results unlikely (Perneger, 1998). Therefore effect sizes were

calculated to provide a description of between-group differences without

concern for sample size. In order to control for type I error rate only effect

sizes greater than 1.0 (i.e. between-group differences were greater than the

pooled standard deviation) were deemed large and of statistical importance.

Changes in muscle co-contraction (sprint run) and muscle activity onset times

(VJ) for gluteus maximus and psoas major (GL/HF), and vastus lateralis and

biceps femoris (VL/BF) muscle pairs were compared between the groups

(again, comparisons were only made for ten subjects. As such, comparisons

were made between weight-trainers and SJ subjects) by Repeated Measures

ANOVA. ‘Group’ and ‘movement phase’ were submitted as between-group

factors.

For all Repeated Measures ANOVA’s, power analysis was also performed to

examine the likelihood that significant effects could be detected. When power

was low (power < 0.8) effect sizes were calculated on near-significant results

(p<0.1) to examine differences without concern for sample size. When

significant group effects were revealed, Tukey’s HSD post-hoc analysis was

used to determine differences between the three groups. For all analyses,

significance was set at an alpha level of p<0.05, unless otherwise stated.

148

7.3 RESULTS

7.3.1 Performance Changes with Training

There were no differences between the groups’ performances either before or

after the training in any strength, VJ or sprint test. There was however an

effect of time (p< 0.01) such that, for many strength and performance

measures, subjects improved over the five weeks of training. Pre- and post-

training test performances of all subjects (pooled) are presented in Table 7.2.

Test Variable Pre-test 95% CI Post-test 95% CI Mean

Change

p-value

10 m sprint (s) 1.91 1.78-2.02 1.86 1.77-1.95 -0.05 <0.05

20 m sprint (s) 3.26 3.00-3.47 3.22 3.05-3.40 -0.04 NS

VJ 1L (m) 0.29 0.25-0.33 0.28 0.25-0.32 -0.01 NS

VJ 2L (m) 0.40 0.34-0.46 0.41 0.36-0.46 +0.01 NS

FHS 1L iso (N) 1186 1030-1342 1455 1256-1654 +269 <0.01

FHS 2L iso (N) 1817 1558-2077 2108 1827-2389 +291 <0.01

FHS 2L 40% F (N) 1249 1055-1444 1277 1091-1463 +28 NS

FHS 2L 70% F (N) 2012 1721-2304 1952 1703-2201 -60 NS

FHS 2L 40% Velp (m.s-1) 1.60 1.51-1.68 1.19 1.14-1.24 -0.41 <0.001

FHS 2L 70% Velp (m.s-1) 1.13 1.04-1.23 1.19 1.14-1.24 +0.06 NS

SQ iso F (N) 1731 1573-1889 1743 1589-1896 +12 NS

SQ 30% F (N) 1937 1729-2145 2048 1866-2230 +111 <0.05

SQ 60% F (N) 2327 2022-2632 2374 2126-2622 +47 NS

Table 7.2. Pre-training, post-training and change scores for sprint, VJ, FHS and Squat tests (allsubjects pooled). There was an increase in some strength measures and decrease in 10 msprint time (p<0.05). There were no between-group differences.

NS – Not statistically significantVJ – vertical jump, FHS – forward hack squat, SQ – squat.iso – isometric contraction30%, 40%, 60%, 70% - load as a percent of isometric maximumVelp – Peak movement velocity1L – single-leg2L – double-leg

149

7.3.2 Isokinetic Knee Extension Torque

7.3.2.1 Angle of peak torque

Reliability of measures of the angle at which peak torque was produced (APT

– Angle of Peak Torque) were poor at 180o.s-1, but were good at 30o.s-1 (see

Table 7.3). Thus changes in APT were analysed only for the slow speed.

There was a near-significant (p<0.07) increase in APT (i.e. the knee angle

was closer to 90o) when all subject data was combined for all groups,

however there was no difference between the groups (see Table 7.4).

Statistical power was low for both main effect (Power = 0.44) and interaction

(Power = 0.39) analyses making it unlikely that significant effects would be

seen. Effect sizes (ES) were thus calculated to examine performance

changes without concern for subject sample size. The effect statistics

suggest that changes in APT may have differed between SQ and FHS (ES =

0.71) and SQ and SJ (ES = 0.90) groups with the knee angle for SQ subjects

being greater (more flexed) after training. Low subject numbers in the present

study may therefore have prevented significance being reached.

Angular Velocity Statistic Score Lower 95% CI Upper 95% CI

30o.s-1 Change in mean 0.61o -2.54 1.32

ICC 0.85 0.64 0.94

180o.s-1 Change in mean 1.18o -1.56 3.91

ICC 0.63 0.26 0.84

Table 7.3. Reliability statistics for angle of peak torque. Inter-repetition reliability for the slow(30o.s-1) movement was better than for the fast movement (180o.s-1).

150

Pre-testing Post-testing

Mean (o) SD Mean (o) SD

FHS 65.7 9.3 67.3 5.9

Squat 62.0 6.9 68.3 3.5

Sprint/jump 61.1 11.9 61.4 6.4

7.3.2.2 Velocity-specific isokinetic torque changes

Subjects produced more knee extension torque at 30o.s-1 than 180o.s-1 (246.7

± 62.6 Nm and 161.8 ± 45.1 Nm respectively; p<0.001) although there were

no significant between-group differences after training. Thus there were no

training-related changes in isokinetic knee extension torque at either

contraction velocity.

7.3.3 Muscle Size and Architecture

7.3.3.1 Muscle thickness

Mean muscle thickness for each training group at each test occasion is

presented in Table 7.5. There was an overall increase in muscle thickness

after training (p<0.05). However, the increase was not different between the

groups (see Figure 7.5). Thus, muscle thickness generally increased in both

muscles in response to training but the change was not related to the training

performed by the subjects. Given the low statistical power of the tests (power

< 0.6), effect sizes were calculated on near-significant results (p<0.1). At

VLd, muscle thickness of FHS subjects decreased relative to both SQ and SJ

(ES = 0.96 and 1.9 respectively). There was no apparent difference between

SQ and SJ. At VLp, muscle thickness of SQ and FHS increased more than

SJ (ES = 1.18 and 0.78 respectively). At RFd, muscle thickness of FHS and

SJ increased more than SQ (ES = 1.27 and 0.90 respectively). While there

Table 7.4. Angle of peak torque (0o = full extension) pre- and post-testing. There wereno differences between the groups.

151

was a small difference between FHS and SJ (with muscle thickness of FHS

increasing more, ES = 0.43), the difference was small. There were no

apparent differences between the groups at RFp.

Table 7.5. Mean (±SD) pre- and post-test muscle thickness and change in thickness. Meanchange values are rounded to two significant figures and are not calculated from thepreviously-rounded pre- and post-test scores. There were no between-group differences inchanges in muscle thickness, however there was an overall increase in muscle thicknessacross all groups at each muscle site (p<0.05*) except VL d. VL d – vastus lateralis distal, VL p– vastus lateralis proximal, RF d – rectus femoris distal, RF p – rectus femoris proximal.

Muscle Pre-test

Mean (mm)SD

Post-test

Mean (mm)SD

Change*

Mean (mm)95%Confidence interval

SQ VL d 13.0 3.9 13.6 3.8 0.6 -0.4 – 1.6VL p 23.4 4.4 26.0 3.6 2.6 0.8 – 4.3RF d 13.4 2.3 13.6 3.2 0.2 -1.3 – 1.7RF p 24.0 2.6 25.9 2.2 2.4 0.7 – 4.2

FHS VL d 13.9 2.8 11.3 2.8 -2.6 -9.2 – 4.0VL p 20.0 0.8 22.3 1.4 2.3 0.1 – 4.5RF d 11.1 1.6 14.2 2.0 3.1 -0.6 – 6.8RF p 23.0 1.6 25.5 2.6 2.5 0.7 – 4.3

SJ VL d 11.0 0.6 12.4 2.0 1.3 -1.3 – 4.0VL p 21.0 2.1 21.6 1.7 0.7 -0.8 – 2.2RF d 11.4 1.0 13.8 2.8 2.3 -0.7 – 5.4RF p 20.8 3.3 25.0 4.1 4.2 0.9 – 7.5

152

-10

-5

0

5

10

Ch

ang

e o

f th

ickn

ess

(mm

)

-10

-5

0

5

10

Ch

ang

e o

f th

ickn

ess

(mm

) Proximal Vas tus Lateralis

-10

-5

0

5

10

Ch

ang

e o

f th

ickn

ess

(mm

) Distal Rectus Femoris

-10

-5

0

5

10

Ch

ang

e o

f th

ickn

ess

(mm

)

Squat

FHS

Sprint/jump

Proximal Rectus Femoris

Distal Vastus Lateralis

Figure 7.5. Muscle thickness changes for all muscle sites. There was a significant increasein muscle thickness after training (p<0.05) but no difference between groups. Solid barsrepresent mean scores while error bars represent the 95% confidence intervals of thechange in muscle thickness.

153

7.3.3.2 Muscle pennation

Mean pennation for each training group at each test occasion is presented in

Table 7.6. Statistically significant (p<0.05) changes in pennation were only

seen at VLd where pennation increased after SQ and FHS training but

decreased after SJ training (Figure 7.6). Given the low statistical power of the

tests (power < 0.6), effect sizes were calculated on near-significant results

(p<0.2). For both VL p and RF d, squat and FHS groups showed increases in

pennation while SJ decreased. At VL p effect sizes for the differences in

pennation change scores were 1.08 and 0.78 for SQ and FHS respectively

when compared to SJ. At RF d effect sizes were 0.98 and 1.45. Thus there

was a trend toward greater increases in pennation of muscles of SQ and FHS

subjects that should be followed up in future research.

Table 7.6. Mean (±SD) pre- and post-test muscle pennation and change in pennation. There wasa significant difference in the change in pennation between both the SQ and SJ, and FHS and SJfor VL d (p<0.05*). VL d – vastus lateralis distal, VL p – vastus lateralis proximal, RF d – rectusfemoris distal, RF p – rectus femoris proximal.

Muscle Pre-test

Mean (deg) SD

Post-test

Mean (deg) SD

Change

Mean (deg) Confidence interval

SQ VL d 8.3 1.8 8.8 0.8 0.5 -1.4 – 2.4VL p 9.9 2.2 11.4 1.6 1.5 -0.5 – 3.5RF d 4.1 1.1 5.4 1.0 1.3 -0.2 – 2.8RF p 10.9 3.1 10.1 1.7 -0.9 -4.5 – 2.6

FHS VL d 8.8 0.5 9.9 1.8 1.1 -1.4 – 3.7VL p 10.0 3.2 11.3 3.1 1.3 -1.7 – 4.2RF d 4.1 0.6 6.0 1.2 1.9 0.2 – 3.5RF p 8.3 3.6 9.0 2.1 0.8 -7.5 – 9.0

SJ VL d 9.9 0.7 6.8 0.8 -3.1* -4.0 - -2.2VL p 9.6 1.8 9.0 1.6 -0.6 -2.7 – 1.5RF d 5.4 1.4 5.2 2.6 -0.2 -4.4 – 4.0RF p 10.7 5.2 11.3 5.6 0.6 -0.8 – 2.0

154

Figure 7.6. Change in muscle pennation for all muscle sites. At VL d, SQ and FHSincreased pennation while SJ decreased (p<0.05*). There were no other significantchanges. Solid bars represent mean changes in pennation while error bars represent 95%confidence intervals for the change in pennation.

-10

-5

0

5

10

Ch

ang

e in

pen

nat

ion

(d

eg) Distal Vastus Lateralis

-10

-5

0

5

10C

han

ge

in p

enn

atio

n (

deg

) Proximal Vastus Lateralis

-10

-5

0

5

10

Ch

ang

e in

pen

nat

ion

(d

eg) Distal Rectus Femoris

-10

-5

0

5

10

Ch

ang

e in

pen

nat

ion

(d

eg)

Squat

FHS

Sprint/jump


*

155

7.3.3.3 Fascicle length

Mean estimated fascicle length for each training group at each test occasion

is presented in Table 7.7. At VLd, fascicle lengths for SJ subjects increased

while there were no changes in SQ and FHS subjects. This was reflected in a

significant group × time interaction effect where fascicle lengths of SJ subjects

changed differently to both SQ and FHS subjects (p<0.05; Figure 7.7). At VL

p, there was a non-significant trend toward a group × time interaction (p=0.08;

ES = 4.33) such that again, SJ increased while FHS and SQ did not change.

Thus for vastus lateralis, fascicle length did not change for the SQ and FHS

groups, but increased significantly for SJ.

There were no differences between the groups’ fascicle length changes in the

rectus femoris although for the proximal part of this muscle, fascicle length

increased overall after training (p<0.05). Therefore, training group did not

influence fascicle length of the rectus femoris.

Table 7.7. Mean (±SD) pre- and post-test estimated fascicle length and change in fasciclelength. At VL d there was a significant difference in the change in fascicle length between SQand SJ, and FHS and SJ (p<0.05a). There was also a near significant difference between SQ andSJ for VL p (p=0.08b). Estimated fascicle length increased for RF p with no differences betweenthe groups. VL d – vastus lateralis distal, VL p – vastus lateralis proximal, RF d – rectus femorisdistal, RF p – rectus femoris proximal.

Muscle Pre-test

Mean (deg) SD

Post-test

Mean (deg) SD

Change

Mean (deg)95%Confidence interval

SQ VL d 92.2 28.0 88.5 17.1 -3. 7a -24.3 – 16.9VL p 140.0 29.1 133.0 16.2 -6.1b -37.9 – 24.7RF d 170.0 42.1 207.4 69.4 51.6 -53.0 – 128.2RF p 117.9 34.0 216.1 16.5 -6.6 44.3 – 152.2

FHS VL d 78.9 18.6 71.9 22.9 10.5a -31.6 – 19.5VL p 108.1 53.0 113.9 38.6 32.2 -20.0 – 41.0RF d 131.7 11.9 137.7 33.3 37.6 -63.7 – 65.0RF p 160.1 97.0 181.9 64.0 0.6 -180.3 – 240.6

SJ VL d 64.4 7.1 116.0 15.8 67.5a 31.3 – 71.8VL p 129.3 27.0 161.5 24.1 98.3b 9.9 – 54.6RF d 127.3 41.5 194.9 48.8 31.6 -73.1 – 208.2RF p 106.2 29.3 147.8 36.8 41.6 10.9 – 72.3

156

-100

-50

0

50

100

Ch

ang

e in

fas

cicl

e le

ng

th

(mm

)

-100

-50

0

50

100

Ch

ang

e in

fas

cicl

e le

ng

th

(mm

)

Proximal Vastus Lateralis

-250

-125

0

125

250

Ch

ang

e in

fas

cicl

e le

ng

th

(mm

)

Distal Rectus Femoris

-250

-125

0

125

250

Ch

ang

e in

fas

cicl

e le

ng

th

(mm

)

Squat

FHS

Sprint/jump


Distal Vastus Lateralis

*

+

Figure 7.7. Change in fascicle length for all muscle sites. Fascicle length increased for SJat VL d (distal vastus lateralis) while there was no change for SQ and FHS (interactioneffect: p<0.05*). There was also a near-significant difference in the change in fascicle lengthbetween SQ and SJ at VL p (p=0.08+). There were no group differences in fascicle lengthfor rectus femoris. Solid bars represent mean changes in fascicle length while error barsrepresent the 95% confidence intervals for the change in fascicle length.

157

7.3.3.4 Relationship between muscle thickness, pennation and

fascicle length

There was no correlation between changes in muscle thickness and

pennation or between changes in thickness and fascicle length. However,

highly significant correlations were found between muscle pennation and

fascicle length (r = -0.82 – -0.92, p<0.01; Table 7.8). Coefficients of

determination ranged from 0.67 to 0.85, therefore 67% - 85% of the variability

in fascicle length can be accounted for by changes in pennation, or vice

versa. Thus, while there was no relationship between muscle thickness and

pennation changes with training, there was a strong relationship between

pennation and fascicle length changes.

7.3.4 Electromyographic Changes

7.3.4.1 Changes in normalised EMG

Pre- to post-training changes in EMG amplitude (normalised to the greatest

EMG during the movement) were calculated for ten subjects. Of those, four

performed RT (SQ and FHS subjects) while six performed only sprint/jump

training (SJ). While low subject numbers likely yielded low statistical power,

Table 7.8. Results of correlation analysis on pennation and estimated fascicle lengthchanges after training. There was a strong relationship between pennation andfascicle length despite no relationship between thickness and either pennation orfascicle length.

Muscle site tested r r2 p-value

Distal vastus lateralis-0.84 0.71 <0.001

Proximal vastus lateralis -0.82 0.67 <0.001Distal rectus femoris -0.85 0.72 <0.001Proximal rectus femoris -0.92 0.85 <0.001

158

data analysis was performed to determine trends that might have been

significant with a larger sample size. There were no differences between

those subjects who performed RT (SQ and SJ) and those who did not (SJ) in

the changes in normalised EMG during the sprint and VJ when univariate

tests were corrected for type I error rate (Bonferroni correction). Therefore,

effect sizes were calculated for 5% sections of movement to examine the

differences between groups without regard for sample size. A stringent effect

size of 1.0 was taken as a ‘large’ effect (Hopkins, 2000). In some cases

uncorrected p-values from t-tests performed on the data were used to indicate

parts of the movement where between-group differences were notable.

For running acceleration (see Figure 7.8) there was an increase in gluteus

maximus (GL) EMG in the weight-trained subjects from the point at which the

right foot left the ground to approximately the point at which the foot passed

under the body (45% - 70% of movement). No differences appeared for

biceps femoris (BF) although EMG for both groups decreased relative to pre-

training levels during foot-ground contact and then increased prior to foot-

ground contact. Thus BF may have been activated differently after training

regardless of the type of training performed by the subjects. Vastus lateralis

EMG of weight-trained subjects was greater from immediately after the right

foot left the ground to just prior to foot-ground contact (65% - 95% of

movement) suggesting greater muscle activity during the recovery phase of

the stride. For rectus femoris (RF), weight-trained subjects tended to increase

EMG prior to foot-ground contact (65 – 95% of movement) while there was no

change in SJ subjects. Finally, hip flexor (HF; psoas major) activity increased

in SJ subjects early in the foot-ground contact phase, and was elevated in

both groups around toe-off and early in the recovery phase. There was also a

marked decrease in HF activity immediately prior to foot-ground contact (90 –

100%) in weight-trained subjects. A t-test (not corrected for type I error rate)

found a significant difference between EMG changes in weight-trained and SJ

subjects in this part of the movement.

159

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Ch

ang

e in

No

rmal

ised

G

L E

MG

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Ch

ang

e in

No

rmal

ised

B

F E

MG

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Ch

ang

e in

No

rmal

ised

V

L E

MG

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Ch

ang

e in

No

rmal

ised

R

F E

MG

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0 20 40 60 80

Ch

ang

e in

No

rmal

ised

H

F E

MG

% Movement Time

Figure 7.8. Change (±95% CI) innormalised EMG for five thighmuscles during the accelerationphase of a sprint run. There wereno differences between weight-trained subjects (dark line) andsprint/jump subjects (light line) forany muscle. Foot-ground contactoccurred at 0% of movement, thefoot left the ground at 50% ofmovement and then contacted theground again at 100% ofmovement.

GL – Gluteus maximusBF – Biceps femorisVL – Vastus lateralisRF – Rectus femorisHF – Hip flexor (psoas major)

160

For VJ (see Figure 7.9) there was an increase in GL activity in weight-

trained subjects early in the descending phase (0 – 40% of movement) and

during the transition and early ascending phase (50 – 70% of movement).

However, late in the ascending phase, EMG of VL decreased in weight-

trained subjects (70 – 90%). Indeed t-tests revealed a significant (non-

corrected) difference between subjects who performed RT and those that did

not (significant differences from 75 – 80% and 85 – 90% of movement).

Similarly complex changes were seen in BF with the EMG of SJ subjects

decreasing late in the descending phase (35 – 40% of movement) and the

EMG of weight-trained subjects decreasing early in the ascending phase (60

– 70% of movement). Generally though, both groups produced less EMG

after training either late in the descending or early in the ascending phase, but

more during the middle of the ascending phase. There were no between-

group differences in the change in EMG for VL or HF, although for RF the

weight-trained subjects showed less muscle activity early in the descending

phase (5 – 25% of movement) with the difference being significant by t-test

(uncorrected; 5 – 10% of movement).

7.3.4.2 Changes in muscle co-contraction (sprint run) and activity onset

times (vertical jump)

There were no differences between changes in the co-contraction patterns of

weight-trained and SJ subjects in either phase of the sprint run and VJ

movements. While the observed power of the tests was generally poor

(<0.50) no comparisons approached significance. Thus effect sizes were not

calculated to examine the magnitude of differences without consideration for

sample size.

161

-1.5

-1

-0.5

0

0.5

1

1.5

Ch

ang

e in

No

rmal

ised

G

L E

MG

-1.5

-1

-0.5

0

0.5

1

1.5

Ch

ang

e in

No

rmal

ised

B

F E

MG

-1.5

-1

-0.5

0

0.5

1

1.5

Ch

ang

e in

No

rmal

ised

V

L E

MG

-1.5

-1

-0.5

0

0.5

1

1.5

Ch

ang

e in

No

rmal

ised

R

F E

MG

Figure 7.9. Change (±95% CI) innormalised EMG for five thighmuscles during the performance of avertical jump. There were nodifferences between weight-trainedsubjects (dark line) and sprint/jumpsubjects (light line) for any muscle.Forward rotation of the upper body(which signalled the beginning of thedescending phase of the jump)occurred at 0% of movement, thetransition from the descending toascending phase occurred at 50% ofmovement, while the toe left theground at the end of the jump at100% of movement.

GL – Gluteus maximusBF – Biceps femorisVL – Vastus lateralisRF – Rectus femoris

HF – Hip flexor (psoas major)

% Movement Time

-1.5

-1

-0.5

0

0.5

1

1.5

0 20 40 60 80

Ch

ang

e in

No

rmal

ised

H

F E

MG

162

7.5 DISCUSSION

This study aimed to describe short-term changes in both performance and

neuromuscular functioning after concurrent resistance- and sprint/jump

training. It was hypothesised that if rapid, movement pattern-specific changes

occurred the FHS-trained subjects should improve their sprint run more than

the SQ group, while the SQ-trained subjects should improve their VJ more

than the FHS group. The sprint/jump group was incorporated to determine

whether the addition of RT to a program affected performance differently to a

program where no RT is performed.

7.5.1 Performance Changes with Training

Neither RT per se nor the movement pattern of resistance exercises

influenced performance of SQ, FHS, sprint or jump tests. Several

explanations may be offered for the lack of training-specific performance

changes. First, the short (five-week) specific training phase may not have

been sufficient for meaningful changes to occur especially given that training-

induced performance changes are often marginal in athletes who have been

training for long periods (Häkkinen et al., 1987, 1991). However, there were

statistically significant performance improvements for the subjects as a whole

in many of the test variables. This suggests that the training period was long

enough for performance changes to occur. Furthermore, studies investigating

movement-specific changes to RT have shown significant effects after as little

as four weeks (Abernethy et al., 1996; Weir et al., 1994, 1995a,b) when RT is

performed in isolation (i.e. without accompanying task practice).

The lack of training-specific performance changes may also have resulted

from the three training groups each performing elements in training that were

beneficial to test performances, but no single group performing training that

was more advantageous than another group. As such, it is possible that all

163

three training programs offered similar performance benefits over the short

training period used in the present study. Indeed Garnica (1986) observed

similar improvements in upper body, isokinetic muscle power in groups that

trained at slow (60o.s-1) and fast (180.o.s-1) speeds. Alternatively, variability in

subject’s training responses and the low subject numbers (23 in total) might

have made it difficult to show clear performance changes.

Improvements across all training groups may have resulted from subjects

training with extra vigor during the specific training phase. Häkkinen et al.

(1987) showed that improvements in strength and performance of highly

trained weightlifters in a one-year training cycle occurred during those periods

of training where training intensity was higher than normal. Similarly,

performances of subjects in the present study may have been improved if

their training intensity was higher than normal. An increase in training

intensity was likely given the training was somewhat novel. Also, subjects’

motivation might have been improved by the knowledge that their training

sessions were supervised and performance changes were to be assessed

after the training period. Given the likely increase in motivation a general

increase in training intensity and test performance could be expected.

Nonetheless, past research has also shown no performance differences

between groups who perform different types of RT with task training. Sleivert

et al. (1995) reported improvements in cycle ergometer power in subjects who

performed eight weeks of strength training and then six weeks of bicycle

sprint training that were similar to a group that performed sprint training for the

entire 14 weeks. This was despite between-group differences in some of the

physiological parameters measured. As such, examination of performance

changes should not be used as the sole indicator of the influence of combined

resistance- and speed training, especially when training is performed for short

periods. Delecluse et al. (1995) also reported no effect of RT movement

velocity on changes in running acceleration when subjects performed two

resistance and one sprint session a week for nine weeks. A high-velocity

164

training group however improved their maximum running speed more than

a low-velocity group. Thus the results of the present study are similar to other

studies that have examined the effects of combined strength and speed

training on tasks involving high power outputs (eg cycle ergometer or running

acceleration).

7.5.2 Body Position-specific Strength Changes

Although the magnitude and timing of joint angle changes and laterality

differed between SQ and FHS exercises, one would expect that if body

position affected performance then some differences between SQ and FHS

groups would have been found given they had different body positions.

However there were no differences in the training responses between the

groups. Thus, it is possible, if not likely, that body position did not influence

test performances. Alternatively, a difference between the groups would not

have been conclusive evidence of an effect of body position given the other

factors that differed between the tasks.

7.5.3 Joint Angle-specific Strength Changes

Adaptations to RT are often specific to the joint angles through which force is

produced in training (Kitai & Sale, 1989; Lindh, 1979; Weir et al., 1994). In

the present study, the range of motion of the knee joint differed between SQ

and FHS groups with the knee angle of SQ subjects closing to 90o but the

knee angle of FHS subjects only closing to 70o (110o internal knee angle).

Given the 20o difference in knee range of motion between the groups, one

could anticipate post-training differences in the angle at which maximum

torque was produced (APT – angle of peak torque) during the knee extension

task.

Across all subjects, there was a near-significant increase in APT (i.e. shift

165

toward increased torque at greater knee flexion; p<0.07) after training. The

increase was largely due to a shift in the APT of SQ subjects (Mean change =

6.3o ± 4.6) with little change in FHS and SJ subjects. Indeed effect size

statistics suggest that the change in APT for SQ subjects was far greater than

either FHS or SJ (ES = 0.71 and 0.90 for SQ versus FHS and SQ versus SJ

respectively). Changes in APT in that direction could be expected given SQ

subjects moved through a greater range of motion in training than both the

FHS (who trained to an internal knee angle of 110o) and SJ (who only

performed sprint and jump training, both of which require movements of less

than 90o at the knee during propulsive phases). The changes in APT

therefore could be considered evidence that, even during the concurrent

training of short duration performed in this study, angle-specific strength

changes occurred.

The mechanisms responsible for the small differences in APT between the

groups are not known. Certainly neural mechanisms have been implicated in

previous research (Kitai & Sale, 1989; Weir et al., 1994). However no EMG

measures were taken during the knee extension test. Muscular changes

might have also contributed however. Certainly a change in the length-

tension properties of fibres of the quadriceps muscle groups would have

resulted in changes in APT. Again, such changes were not monitored in this

study.

Muscular factors that influence the torque-angle relationship and were

measured in this study include the pennation and fibre length of quadriceps

muscles. The amount of force transmitted along a tendon from a contracting

fibre is inversely related to its angle of attachment, and since fibres of pennate

muscles rotate during muscular contraction, pennation and therefore the loss

of force is greater in muscles with greater pennation. Thus, there is a greater

reduction in relative force producing potential at short muscle lengths in highly

pennate muscles compared to muscles with smaller pennation. In this study,

pennation of the vastus lateralis and rectus femoris was not different between

166

SQ and FHS subjects despite their APT changing differently. Therefore,

unless changes in vastus intermedius or vastus medialis had a significant

effect, it is unlikely that changes in pennation affected the APT of subjects in

this study.

Changes in fibre length can also change the length-tension properties of a

muscle (Goldspink, 1974; Williams et al., 1990). Decreases in fibre length are

associated with increases in passive tension and therefore a reduction in the

length at which optimum force is produced. Again, there were no differences

between SQ and FHS subjects. It is therefore unlikely that fibre length

changes affected APT of subjects.

7.5.3 Laterality-specific Strength Changes

Effects of laterality of training were investigated by comparing the

performances of SQ (who trained bilaterally) and FHS groups (who trained

unilaterally) on unilateral tests. There was no evidence for laterality-specific

adaptations as there were no between-group differences in unilateral VJ,

unilateral FHS or unilateral isokinetic knee extension performance after

training. The result might be due to the short training period or low subject

numbers. However, Tanaguchi (1997) reported significantly greater increases

in bilateral handgrip and leg extension strength after three weeks of training in

subjects who trained bilaterally as compared to subjects who trained

unilaterally. Thus, when resistance exercise was performed in isolation (i.e.

not concurrently with another mode of training) laterality-specific performance

changes seemed to occur rapidly.

It was also possible that the reliability of unilateral tests was low. This would

reduce the likelihood of detecting significant changes. Nonetheless, an

investigation of the reliability of the unilateral and bilateral FHS was conducted

to assess the reliability of uncommon unilateral and bilateral tasks in Study

Three. The research showed that the reliability of both tests were similar.

However, reliability was reduced in both unilateral and bilateral movements

167

when light loads rather than heavy loads were lifted (ICC of unilateral FHS

with 40% and 70% of isometric maximum load were 0.70 and 0.90

respectively; ICC of bilateral FHS at 40% and 70% loads were 0.64 and 0.95

respectively). So poor reliability of unilateral tasks is unlikely to have affected

the results here. As such, the results of the present study might suggest that

early adaptations to concurrent strength and sprint/jump training are not

specific to the laterality of training exercises.

7.5.4 Velocity-specific Isokinetic Torque Changes

Adaptations to RT have also been shown specific to the velocity at which

training exercises are performed (Coyle et al., 1981; Caiozzo et al., 1981;

Wilson et al., 1993). In the present study, greater knee extension torque was

produced across all subjects at 30o.s-1 than at 180o.s-1. However there was

no general increase in torque at either movement velocity and there were no

between-group differences. Therefore, subjects who performed RT did not

show greater improvements in slow speed strength (as measured by an

isokinetic leg extension task at least) nor did subjects who trained only with

high-velocity sprint and jump movements significantly increase their high-

speed strength.

Given that the training performed by the subjects did not involve isokinetic

knee extension, the results could be attributed to poor test specificity

(Abernethy et al., 1995; Wilson et al., 1996). It is worth noting that muscles

with less pennation and shorter fibre lengths are better able to perform high-

velocity contractions (Sacks & Roy, 1982; Kumagai et al., 2000). In the

present study, pennation and fascicle length (used as a measure of fibre

length) decreased in the vastus lateralis muscle of SJ subjects. If these

changes were representative of changes in other vastii muscles, increases in

knee extension velocity could have been expected. Given no velocity-specific

isokinetic knee extension changes were seen it is possible that movement

pattern-specific training was also needed for performance changes to be

168

realised. That is, the testing and training exercises might have had to be

similar. The result therefore highlights the movement pattern-specific nature

of strength adaptations. It is unlikely though that the results of the isokinetic

tests reflect an absence of absolute strength gains after training since

subjects improved their force production in many of the multi-joint resistance

tests.

Mechanisms other than architectural changes have been proposed for

velocity-specific strength gains. Neural adaptations might include increases in

muscle activation (Häkkinen & Komi, 1983, 1985, 1986; Häkkinen et al.,

1985a,b), selective activation of muscles with high fast-twitch fibre content

(Duchateau et al., 1986; Nardone & Schieppati, 1988) and increased motor

unit synchronisation (Moritani et al., 1987). Muscular changes might include

changes in myosin heavy chain (Jansson et al., 1990; Tesch et al., 1989) and

light chain expression (Jostarndt-Fogan et al., 1998; O’Brien et al., 1992),

increases in myosin ATPase activity (Essén et al., 1975) and increases in fast

tropomyosin and troponin isoforms (O’Brien et al., 1992). Given the

numerous changes that result in increases in movement-velocity, or force at a

given movement velocity, it seems likely that changes in high-speed isokinetic

knee extension, sprint or jump tests would have been seen if significant

adaptations had occurred. It therefore appears that there were few changes

other than muscle architecture.

7.5.5 Changes in Muscle Architecture

7.5.5.1 Training effects on muscle pennation and fascicle length

Muscle architecture of vastus lateralis changed in accordance with changes

that have been previously reported in the literature (Kawakami et al., 1995;

Kumagai et al., 2000). For subjects who performed RT as part of their training

program, muscle pennation increased while fascicle length decreased. For

169

SJ subjects, who performed only high-velocity training, pennation

decreased while fascicle length increased. Greater pennation and shorter

fascicle lengths are reported to be prominent in muscles that regularly perform

high-force, low-velocity contractions (Burkholder et al., 1994; Van Eijden et

al., 1997) whereas muscles that participate more regularly in movements of

high velocity tend to possess smaller pennation and longer fascicle lengths

(Burkholder et al., 1994; Kumagai et al., 2000). Indeed the length of a muscle

fibre has been theoretically and experimentally shown to be related to the

fibre’s contraction velocity (Burkholder et al., 1994; Sacks & Roy, 1982;

Wickiewicz et al., 1983). Until recently however, no research had shown a

relationship between muscle architecture and the performance in complex

tasks until Kumagai et al. (2000) reported a high correlation between 100 m

sprint performance and fascicle length of leg musculature (faster sprint times

correlated with longer fibres). Furthermore, while changes in pennation have

been more extensively researched and the relationship between pennation

and physical performance highlighted (Kawakami et al., 1993, 1995), no

research has examined muscle architecture changes when both high-velocity

and high-force training has been performed concurrently.

The results of the present study suggest that high-velocity training in the

absence of low-velocity, high-force training was associated with a decrease in

pennation and increase in fascicle length. One could deduce from this that

the length of muscle fibres increased in subjects who performed only high-

velocity training (assuming muscle fibre length is synonymous with fascicle

length). Also, when RT was performed with the high-speed training (in the

present study the quantity of high-speed training was also reduced for the

weight training groups) muscle architecture changes were similar to those

seen in muscles that participate often in high-force contractions. Given this,

the muscle architecture of SJ subjects appeared to adapt to produce higher

velocity contractions. The muscle architecture of SQ and FHS subjects,

despite subjects in these groups also performing high-velocity training,

adapted to produce contractions of higher force.

170

For rectus femoris, muscle architecture changes were less consistent.

Pennation increased in the distal part of the muscle in SQ and FHS subjects

compared to SJ suggesting similar changes to vastus lateralis. However no

changes were seen at the proximal site and no changes were seen in fascicle

length. The inconsistent results might be attributed to the complex functioning

of this biarticular muscle. During most multi-joint lower limb movements (eg

pushing movements), knee extension and hip flexion occur simultaneously, as

do knee flexion and hip extension. As such, even during movements where

the joint ranges of motion are large, the length of rectus femoris muscle may

change little but instead act almost isometrically to transfer force (or more

correctly joint power) from the hip to the knee (Bobbert & Ingen Schenau,

1988, 1992; Jacobs et al., 1993; Van Soest et al., 1993). Given that pushing

movements are performed frequently in sport, the training stimulus provided

to the rectus femoris may not have been sufficiently unique to promote

architectural changes.

7.5.5.2 Training effects on muscle thickness (hypertrophy)

Muscle hypertrophy is not only well correlated with strength levels in humans,

but is considered important for continued strength increases in well trained

athletes (Jones, 1992; Narici et al., 1989). Since the ability to produce power

in movements depends on both the speed and force of muscle contraction,

larger and stronger muscles may contribute to greater power production. In

the present study there was a significant increase in muscle size of rectus

femoris and vastus lateralis (as estimated by muscle thickness changes)

across all subjects. However the increase was not different between the

groups. Effect statistics suggest there were some differences in hypertrophy

among the groups, but these changes were small and inconsistent. There

was no apparent effect therefore of RT per se or the movement pattern of

training exercises on hypertrophy. Whether the five-week training phase was

too short for significant differences in hypertrophy to be seen is unclear.

171

However given there were significant increases in muscle thickness over

the training period across all subjects one would have to assume that training-

related differences in hypertrophy would occur only in the long term.

It is perhaps of interest to note that muscle thickness increases were as large

for SJ as they were for FHS and SQ. Given hypertrophy is often associated

with RT, it is unclear how hypertrophy occurred in SJ. One theory is that the

hypertrophy in SJ muscles reflected the accumulation of fluid within the

muscle. The accumulation of metabolites during exercise triggers osmotic

changes that pull plasma into the muscle cells. Therefore the muscles of SJ

subjects may have become more ‘full’ as a result of their high-intensity

training. A second theory is that the training promoted increases in

sarcoplasmic material (Nikituk & Samoilov, 1990). Namely, increases in

creatine phosphate, free creatine, ATP and glycogen stores, as well as some

increase in capillarisation may have occurred (Fleck & Kraemer, 1988;

MacDougall et al., 1977). However, given the subjects often performed sprint

and jump training, and performed a four-week familiarisation, significant

increases in fluid within the muscle and greater sarcoplasmic content (an

acute exercise response) would not have been expected unless training was

of higher-than-normal intensity (a point that was discussed earlier).

Furthermore, at least four days separated the final training session and the

assessment of muscle thickness. This period would have allowed much of

the muscle volume associated with the acute exercise response to subside.

As such, it is unlikely that these two mechanisms would have been solely

responsible for the increase in muscle thickness of SJ subjects.

Another theory is that some selective hypertrophy of type II muscle fibres

occurred over the training period as training volume increased. Hypertrophy

of type II fibres has been shown to occur within weeks of beginning sprint-type

training (Mero et al., 1983; Sleivert et al., 1995). Indeed Sleivert et al. (1995)

showed that both fast- and slow-twitch fibres areas increased in a sprint-

trained group (10 s cycle sprints) similarly to a resistance-trained group in an

172

eight week training regime using untrained subjects. Again however,

hypertrophy of fast-twitch fibres of the subjects in the present study could be

expected to be small given the subjects’ training history and their lack of

improvement in high-speed isokinetic knee extension.

A final theory is that, despite the pennation of vastus lateralis muscles of SJ

subjects becoming smaller after training, increases in fibre length may have

resulted in increases in muscle thickness. Increases in pennation are often

accompanied by decreases in fibre length (Benninghoff & Rollhauser, 1952;

Burkholder et al., 1994), so the opposite would also be likely. However, given

that muscle thickness is a function of muscle pennation and fibre length

(MT=FL•sinθ, where MT = muscle thickness, FL = fascicle [fibre] length and θ

= pennation), if fibre length increases were of greater proportion to pennation

reductions then an increase in fibre length would cause an increase in muscle

thickness, regardless of actual fibre hypertrophy. More likely, the hypertrophy

seen in the present study reflected a combination of adaptations. Whether the

rate of hypertrophy seen here would have continued with further training is

unclear.

7.5.5.3 Relationship between Muscle Thickness, Pennation and Fascicle

Length

Much research has investigated the relationship between muscle size

(especially muscle thickness) and pennation. While it is logical that increases

in muscle size are coupled with increases in pennation to allow more muscle

tissue to attach to a given area of tendon (Kawakami et al., 1993; Rutherford

& Jones, 1992), research has shown inconsistent results. Both cross-

sectional and longitudinal studies have investigated the relationship with some

finding a relationship (Kawakami et al., 1993, 1995, 2000) and others not

finding a relationship (Henriksson-Larsén et al., 1992; Rutherford & Jones,

1992) between the two architectural features. Therefore, correlation analysis

173

was used in the present study to further assess the relationship between

the different architectural measures. There was no correlation between

muscle thickness and pennation. Therefore changes in muscle thickness

appeared not to be related to changes in pennation supporting the reports of

Henriksson-Larsén et al. (1992) and Rutherford and Jones (1992)

There was however a significant relationship between muscle pennation and

estimated fascicle length. Indeed, between 67% and 85% of the variability in

fascicle length can be attributed to changes in pennation, or vice versa. The

result is in agreement with other research showing a similar relationship

between pennation and fascicle length where longer fibres tend to attach at

smaller angles to the tendon (Burkholder et al., 1994; Henriksson-Larsén et

al., 1992; Lieber & Blevins, 1989; Sacks & Roy, 1982). Since there was no

correlation between muscle thickness and fascicle length, one may speculate

that fascicle length change occurred independently of muscle thickness.

Given however that pennation and fascicle length were highly correlated and

changed differently between the groups (decrease in pennation and increase

in fascicle length in SJ compared to SQ and FHS), the movement velocity and

force requirements of training exercises might have affected pennation and

fascicle length

7.5.6 Muscle Recruitment Pattern Changes with Training

7.5.6.1 Changes in EMG amplitude or ‘neural drive’

The recruitment timing and magnitude of agonist (Buchanan et al., 1989;

Buchanan & Lloyd, 1997; Theeuwen et al., 1994), antagonist (Buchanan et

al., 1986, 1989; Sergio & Ostry, 1995) and stabilising muscles (Oddsson &

Thorstensson, 1990) has been shown to change when forces are applied in

different directions and at different joint angles. For example, Nakazawa et al.

(1993) found that the recruitment of brachioradialis and biceps brachii

174

muscles changed depending on the range of motion through which the

elbow joint moved (0-30o, 30-60o and 60-90o) and the mode of contraction

(concentric or eccentric). One might expect therefore that chronic training

could alter muscle contraction patterns (Carolan & Cafarelli, 1992; Moritani,

1992; Sale, 1992).

In the present study, changes in normalised EMG during the acceleration

phase of a sprint run were inconsistent between subjects. Generally however,

subjects who performed weight training exhibited greater gluteus maximus

(GM) activation during the recovery part of the stride cycle and greater biceps

femoris (BF), vastus lateralis (VL) and rectus femoris (RF) activation

immediately prior to foot-ground contact (see Figure 7.8). The increase in GM

activity during the recovery phase could be considered counterproductive

since hip flexion is the predominant movement in this phase. The increases

in BF, VL and RF activity possibly helped prepare for foot-ground contact. For

SJ subjects there was little change in normalised EMG throughout the stride

cycle, although a slight increase in hip flexor (HF) activity could be seen early

in the foot-ground contact phase and early in recovery (Figure 7.8). The

importance of the increase in activity in the foot-ground contact phase is

unclear, but might allow greater control of the leg during ground contact. The

increase early in recovery however seems important since one would expect

greater hip flexor force to improve the speed of leg recovery. As such, more

change can be seen in the EMG patterns of subjects who performed

resistance training. It is possible that most of these changes are

counterproductive.

For the VJ, a marked decrease in RF activity was seen early in the

descending phase followed by increases in GM activity during the transition

from descending to ascending phases (see Figure 7.9). Furthermore, there is

a marked decrease in GM EMG prior to the end of the jump. The decrease in

RF activity early might suggest a more passive beginning to the jumping

movement whereas the increase in GM activity in the transition phase and

175

decrease late in the jump suggests that GM was contributing to force

earlier in the jump. Given that greater hip extension torque can be transferred

to the knee and ankle joints by the biarticular muscles (RF and

gastrocnemius) and that earlier increases in muscle activity are associated

with greater jumping performance (Bobbert et al., 1996; Voigt et al., 1995), the

change in GM activity may be beneficial to jump performance.

Few changes were observed in EMG activity of SJ subjects, although a slight

decrease in BF activity early in the transition phase and an increase in activity

during the ascending phase suggests that activation of this muscle was

altered after training (Figure 7.9). Given the biceps femoris is a hip extensor

(and knee flexor) the increase in activity during ascent may be beneficial.

Again then, greater (non-significant) changes were seen in subjects who

performed weight training, however for the VJ, the changes may have been

more productive than for the sprint run.

Given these results, it could suggested that RT influenced muscle recruitment

patterns. For weight trainers the changes may have affected their efficiency

during the acceleration phase of a sprint run, but for the VJ these changes

might have improved performance. For SJ subjects, muscle recruitment

patterns appeared not to change significantly. It appears therefore that the

provision of RT in addition to sprint and jump training may, even in training

periods of only a few weeks, influence muscle recruitment patterns. These

changes however did not significantly affect their sprint or jump test

performances. Unfortunately data were only available for ten subjects. Also

inter-subject variability was high (see 95% confidence intervals in Figures 7.5

& 7.6). Thus it was difficult to make clear conclusions about muscle

recruitment strategies. Also, longitudinal changes in EMG are difficult to

detect using surface electrodes since exact replication of the preparation and

positioning of electrodes is impossible. Nonetheless, future research may be

compared to the current research and a more clear idea of muscle contraction

changes gained.

176

7.5.6.2 Muscle co-contraction and muscle activation onset changes

Some authors have suggested that movement-specific adaptations to training

are partially attributable to changes in muscle co-contraction (Weir et al.,

1994, 1995b). Certainly, antagonistic co-contraction may be modified after

training (Baratta et al., 1988; Carolan & Cafarelli, 1992). Thus, co-contraction

patterns of subjects who performed weight training could be expected to

change. However no differences were observed in co-contraction during the

acceleration phase of the sprint run in either group. Furthermore, there were

no changes in EMG onset times during the VJ. While the small sample size

and high variability of test performances may have masked significant

findings, none of the variables investigated approached statistical

significance. As such, there was no evidence that muscle co-contraction

patterns (for the sprint run) or activation onset times (for the VJ) were altered

during training. Thus it is unlikely that the training performed here was

sufficient to promote such changes. One can consider that short duration RT

has little effect on muscle contraction sequences and therefore on

performance.

7.5.7 Practical Implications

There were no performance differences between those athletes who

performed RT and those that did not. Generally all groups improved their

performance in strength and power tasks but showed no marked improvement

in sprint (except 10 m sprint time) and jump performance. Nonetheless, there

was some evidence that changes had occurred in muscle architecture and in

the nervous system. Furthermore, there was evidence of angle-specific

training changes in SQ subjects. Given that the muscle architecture of

subjects who performed resistance exercises adapted in a way thought to

produce higher force contractions, whereas muscles of SJ subjects adapted

to produce higher velocity contractions (Burkholder et al., 1994; Kawakami et

177

al., 1993, 1995), it could be suggested that the incorporation of RT into a

longer training plan could have a negative impact on movement speed.

Nonetheless, power rather than pure speed is often required for successful

performance in sport. Since power production requires a combination of both

muscle force and contraction velocity, an absence of training that can

enhance muscle force could also have long-term detrimental effects.

Of interest here though was that muscle architectural changes occurred

rapidly. Data presented in this study may provide a solution to the problem of

how to use RT to improve muscle force characteristics without compromising

contraction speed (at least from a muscle architecture point of view). Strength

and speed training could be performed concurrently in a training regime. The

speed training (often representing task training) would improve the efficiency

of task performance and promote changes that improve muscle contraction

velocities while RT would improve the force of muscle contractions. Then,

several weeks from a major competition (or whatever the season’s focus) RT

could be phased out. Muscle architectural changes might then rapidly adapt

to the speed training, muscle activation patterns that may have been

compromised by RT may revert closer to optimum, and fatigue and muscle

damage synonymous with RT could be reduced. Thus optimum conditions

would exist for high-speed or powerful movements. Taper periods commonly

used by athletes would probably serve this purpose.

There was less evidence to suggest that movement pattern-specific changes

occurred in the present study with only some change in the angle at which

peak isokinetic knee extension torque was produced in SQ subjects.

Unfortunately, no comparisons could be made between SQ and FHS subjects

regarding muscle activation changes because data was only collected for a

small number of subjects. However, past evidence, and evidence from the

knee extension test in the present study, suggests that the movement pattern

of training exercises has some effect on movement efficiency (Baratta et al.,

1988) and strength expression (Kitai & Sale, 1989; Lindh, 1979; Weir et al.,

178

1994; Wilson et al., 1996). If this is indeed true, then athletes should use

resistance exercises that mimic the task they wish to improve.

179

CCHHAAPPTTEERR 88:: TTHHEEOORRYY OONN

EEAARRLLYY AADDAAPPTTAATTIIOONNSS TTOO

RREESSIISSTTAANNCCEE TTRRAAIINNIINNGG

180

8.1 DOCUMENTATION OF THEORY

There is much contention as to the process of neuromuscular adaptation to

RT. Commonly, neural adaptations are believed to occur prior to muscular

changes, however much evidence suggests that changes to sarcomere

length, fibre size, and muscle architecture can occur within hours or days of a

stimulus. It is therefore possible that adaptations in the nervous system are

secondary to muscular changes. That is, the nervous system adapts to the

‘new’ muscle forged by training. As such, the purpose of this chapter is to

speculate as to the process of neuromuscular adaptation to RT or concurrent

RT and speed training.

8.1.1 Are strength changes related to muscle activation?

Early changes in strength during a period of RT have traditionally been

ascribed to adaptations within the neural system (DeVries, 1968; Narici et al.,

1989; Sale, 1988). This is most likely due to research showing that early

strength changes were related to changes in muscular electrical activity (i.e.

increases in EMG) rather than changes in muscle size (e.g. Moritani, 1992;

Narici et al., 1989). It was suggested that strength increases resulted from

greater activation of muscle rather than increases in the size or number of

contractile elements. Indeed, early research using electrical muscle

stimulation suggested that, after training, those subjects who were unable to

fully activate their muscles during a contraction were able to do so after

strength training (Jones & Rutherford, 1987; Rutherford & Jones, 1986).

However more recently, the idea that untrained subjects could not fully

activate their muscles to the same degree as their strength-trained

counterparts has been questioned (Behm & St-Pierre, 1998; Cafarelli &

Fowler, 1993). While research has shown that untrained subjects could not

fully activate their muscles (Allen et al., 1995; Belanger & McComas, 1981;

181

Dowling & Cardone, 1994; Lloyd et al., 1991; Strojnic, 1995) complete

muscle activation has been shown to occur in untrained subjects (Bellemare

et al., 1983; Gandevia & McKenzie, 1988; Rutherford et al., 1986).

Presenting the results of training studies, some researchers reported that

most or all subjects could fully activate their muscles prior to training

(Garfinkel & Cafarelli, 1992; Jones & Rutherford, 1987; Rutherford & Jones;

1986) and Sale et al. (1992) did not find a change in subjects’ quadriceps

activation after dynamic RT. More recently, Lyle & Rutherford (1998) and

Martin et al. (1994) showed that increases in strength occurred after

stimulation training where motor commands were not required in training.

Also, Herbert et al. (1998) showed increases in strength only occurred in

subjects who weight trained but not in subjects who performed imagined

contractions. There was also no change in muscle recruitment (estimated by

a sensitive form of the electrical stimulation technique) after training. These

studies provide further evidence that short-term changes need not result from

an increased recruitment of muscle.

Therefore, other factors might explain the increases in EMG seen with weight

training. For example Yao et al. (2000) reported that greater surface EMG

occurs concomitantly with greater motor unit synchronisation. Also, increases

in muscle mass (Alway et al., 1992; Bell & Jacobs, 1990; Hortobágyi et al.,

2000) and decreases in radial packing density (Claassen et al., 1989; Horber

et al,. 1985; Jones & Rutherford, 1987) after RT might allow more active

tissue to be located within the pick-up area of a surface electrode. Similarly,

reduced EMG signal filtering could be expected with decreases in

subcutaneous and/or intra-muscular fat that might accompany training. It is

very possible then that increases in EMG after RT do not reflect increased

muscle activation. Thus, early strength improvements might result from some

other mechanism in addition to, or exclusive of, muscle activation changes.

182

8.1.2 How does muscle strength increase with resistance training?

In view of conflicting evidence as to the cause of the increase in EMG with

RT, mechanisms involving systems other than the nervous system must also

be considered. Hypertrophy is rarely suggested to be a factor in early

strength adaptation (Narici et al., 1989). This is largely because changes in

muscle thickness, cross-sectional area or volume are significant only weeks

after training onset. However it may be possible that early fibre hypertrophy

cannot be detected by anthropometric, ultrasound or magnetic resonance

imaging techniques. Needle biopsy studies have shown Increases in fibre

area within weeks of the commencement of training (Esbjörnsson-Liljedahl et

al., 1996). Furthermore, significant fibre hypertrophy (up to 30%) has been

seen in electrically-stimulated rabbit muscle after only four days. However

increases in radial packing density (Claassen et al., 1989; Horber et al,. 1985;

Jones & Rutherford, 1987) or decreases in intramuscular fat could minimise

changes in muscle cross-section or volume. Furthermore, a change in the

size and pennation of fibres in pennate muscles occurs with a decrease in

fibre length (Benninghoff & Rollhauser, 1952; Muhl, 1982). Such adaptations

would minimise muscle volume changes to allow the muscle to better fit within

its compartment (Benninghoff & Rollhauser, 1952; Burkholder et al., 1994).

Thus, muscle size changes might not be readily detected by ultrasound or

MRI techniques. However the dismissal of muscle hypertrophy as a factor

involved in strength increases with RT is perhaps unwarranted.

Muscle architecture is hypothesised to affect muscle function in that larger

angles of pennation and shorter muscle fibres are beneficial to higher-force

contractions (Burkholder et al., 1994; Kumagai et al., 2000; Sacks & Roy,

1982; Van Eijden et al., 1997; Wickiewicz et al., 1984). While fibre lengths

have been shown to change rapidly, no studies have thoroughly examined the

time course of pennation changes. Certainly however, such changes occur

within weeks (Henriksson-Larsén et al., 1992). The results of the present

thesis also suggest this. Some authors hypothesise that increases in

183

pennation are a response to muscle hypertrophy allowing more contractile

tissue to attach to a given area of tendon (Kawakami et al., 1993; Rutherford

& Jones, 1992). However poor relationships between muscle size (thickness

or fibre area) and pennation have been shown (Blazevich & Giorgi, 2001;

Blazevich et al., 1998; Henriksson-Larsén et al., 1992; present thesis). Also,

Rutherford and Jones (1992 [longitudinal study]) found no relationship

between changes in muscle size and changes in pennation, and no

relationship was seen between the two in the present thesis. So pennation

changes do not seem to mirror changes in muscle hypertrophy.

8.1.3 How would muscle architecture affect strength?

In Study Five of this thesis all training groups showed similar increases in

muscle size, although only the groups that performed RT showed greater

pennation of the vastus lateralis. This suggests perhaps that the stimulus

provided by RT influenced pennation changes. Theoretically this makes

sense. The muscle length change of highly-pennate muscle is greater for a

given length of fibre shortening since fibres not only shorten during

contraction, but rotate. So sarcomeres in a pennate muscle could probably

work closer to their optimum lengths during a dynamic contraction (Muhl,

1982). There is good theoretical evidence therefore that pennation should

increase in response to high-load training even before hypertrophy occurs.

The shorter fibres in muscles with greater pennation might point to another

mechanism by which strength can be improved. Force from sarcomere

shortening is transmitted through all of the serially-arranged sarcomeres

within a fibre. Thus, force produced by the contracting fibre can only be as

great as the weakest sarcomeres. Indeed, when force produced by one

sarcomere has to be transmitted through other sarcomeres, energy will be lost

at each sarcomere. Thus, fibre contraction force could be greatest when only

a small number of sarcomeres are arranged in series. Improved force

production however would be attained from many parallel columns of

184

sarcomere strings.

Moreover, shorter fibres tend to possess longer sarcomeres. The longer

sarcomeres would have longer actin and myosin filaments. Assuming all

fibres of a given species of animal have a similar number of cross-bridges per

unit length of filaments, and similar likelihood for cycling of cross-bridges,

longer sarcomeres would have more actin-myosin attachments and provide

greater contractile force. So decreases in fibre length (and increases in

sarcomere length) would benefit high force production by allowing more

cross-bridges per sarcomere to produce force.

Early losses of sarcomeres in series could also minimise the energy cost of

muscle hypertrophy if it mirrored increases in sarcomeres arranged in parallel.

The energy saved, or absorbed, by sarcomere loss could be used to build

more sarcomeres in series. Therefore, early increases in fibre area would be

cost-effective. Longer-term hypertrophy that involves increases in

sarcomeres arranged in parallel, with no further decreases in sarcomeres

arranged in series would only occur if the stimulus for strength increases were

chronic. Therefore, muscles with both greater pennation and shorter fibres

may be better for contractions involving high forces.

8.1.4 Is there a neural explanation for angle-specific strength changes?

Adaptations to strength training have been shown to be highly specific

(Abernethy & Jürimäe, 1994; Lindh, 1979; Rutherford et al., 1986; Thépaut-

Mathieu et al., 1988; Weir et al., 1995a). Therefore, strength gained by the

performance of one task does not necessarily translate to strength in another

task. Most clearly, strength adaptations are specific to the joint angle (or

muscle length) at which training is performed (Kitai & Sale, 1989; Weir et al.,

1994). No single mechanism has been proven responsible for the angle-

specific adaptations reported by such investigators. Kitai and Sale (1989)

suggested that neural mechanisms were likely since angle-specific

185

plantarflexor strength changes were seen in voluntary but not stimulated

contractions. However many studies have not shown changes in muscle

activation after RT (Brown et al., 1990; Carolan & Cafarelli, 1992; Harridge et

al., 1999; Herbert et al., 1998; Sale et al., 1992). The lack of changes is

perhaps due to muscle activation being nearly maximal in most subjects

(Carolan & Cafarelli, 1992; Garfinkel & Cafarelli, 1992). It has also been

suggested that such techniques are not sensitive enough to detect small

changes in muscle recruitment (Allen et al., 1995; Gandevia et al., 1995).

Further evidence for a neural explanation for angle specificity was provided by

Weir et al. (1994) who showed angle-specific changes in both a trained and

untrained limb. They hypothesised that strength increases seen in the

untrained limb indicated that neural mechanisms were involved. However

Srihari (1981) reported changes in myosin light chain expression of the soleus

muscle in a control limb after cross-innervation of soleus with gastrocnemius.

Therefore muscular changes can occur in a control limb, even in the absence

of training or learning. Thus cross-education may not be evidence for a

neural explanation for angle-specific strength changes.

Other studies have also not shown changes in surface EMG with angle-

specific strength changes (Weir et al., 1994, 1995b). Further, angle-specific

torque changes have been shown with electrical muscle stimulation training

where central motor commands are not required (Martin et al., 1994). Despite

neural mechanisms being held most likely responsible for angle-specific

strength changes, no research has definitively shown this to be the case.

Therefore, adaptations that do not involve changes in the nervous system

resulting from the learning process might be involved in the angle-specific

strength adaptations seen with resistance training.

8.1.5 How could muscle strength increase in an angle-specific manner?

Sarcomere length has been shown to change not only in response to periods

186

of immobilisation at lengths greater or lesser than rest length (Tabary et al.,

1972; Goldspink et al., 1974; Heslinga et al., 1995) but also in response to

imposed stretch (Williams, 1990), stretch combined with electrical stimulation

(Williams et al., 1986) and downhill running (Lynn & Morgan, 1994).

Therefore, sarcomere adaptation may occur in response to an imposed load.

Herring et al. (1984) found that masticatory muscles’ optimum length for force

production was most related to the length at which maximum force was

required in vivo. Thus, sarcomere length might adapt to a new length should

resistance-type training be performed at a given muscle length. This could

explain the angle-specific strength adaptations shown in some studies (see

Koh, 1995).

Sarcomere length affects the active length-tension relationship of muscle.

Although elastic and viscous properties of a muscle affect its length-force

relationship (Gillard et al., 2000), active muscle force is usually greatest near

the length of optimum filament (actin-myosin) overlap. A slight change in the

length of optimum overlap would alter the length at which the fibre produces

optimum force. However, in pennate muscles, length-tension properties are

more complex. The force produced along the length of a tendon is reduced

as the angle at which fibres attach to the tendon is increased (Burkholder et

al., 1994; Wottiez et al., 1983). In pennate muscles, muscle shortening is

caused not only by fibre shortening, but also by rotation of those fibres (Muhl,

1982). As such, the angle of fibres to the tendon increases as the muscle

shortens and the proportion of fibre force acting along the tendon is reduced.

The greater the pennation of a muscle, the earlier in a contraction fibre

rotation becomes significant and force declines. Therefore, a muscle’s length-

tension characteristics are influenced, among other things, by both the length-

tension characteristics of its constituent fibres the angle they attach to the

tendon (or aponeurosis).

While the length of sarcomeres influences the properties of a muscle,

sarcomere length is heterogeneous throughout the muscle (Scott et al., 1993;

187

Van Eijden & Raadsheer, 1992; Willems & Huijing, 1994). Therefore, for a

given shortening of muscle, some fibres will shorten more than others (Weijs

& Van der Wielen-Drent, 1983; Van Eijden & Raadsheer, 1992). It would be

more efficient perhaps for motor units at near-optimum lengths to contract in

most contractions while those on their descending limb could lengthen to

provide passive force and improve force transmission through the muscle

fibres.

Indeed motor units of some longer muscles are not randomly distributed

throughout a muscle and are not equally likely to be recruited, but are

grouped as sub-populations or ‘functional compartments’ based on the

likelihood of their activation during a given contraction (Segal, 1992). For

example, the biceps brachii appears to contain a group of motor units that are

readily recruited during arm flexion but a separate group that are readily

recruited during forearm supination (Ter Haar Romeny et al., 1982; 1984;

Theeuwen et al., 1994; Van Zuylen et al., 1988). Such compartmentalisation

has also been shown in muscles such as the human masseter (Tonndorf &

Hannam, 1994) and cat lateral gastrocnemius (English & Weeks, 1984).

Further evidence that selective activation of compartments can increase the

number of sarcomeres in a region of muscle has been provided by studies

showing selective hypertrophy of certain regions of muscle. Narici et al.

(1989) found that hypertrophy of the quadriceps was greater in vastus

medialis and vastus intermedius than rectus femoris and vastus lateralis after

isokinetic strength training. Furthermore, Housh et al. (1992) reported

significant increases in vastus lateralis and vastus intermedius cross-sectional

area at the mid-level and in rectus femoris across the entire muscle following

isokinetic strength training. In the present study, there was evidence that

hypertrophy of parts of vastus lateralis and rectus femoris differed depending

on the training performed by subjects.

Therefore, continued selective recruitment of muscles and sections of

188

muscles may result in selective hypertrophy of these regions. Given that

muscle hypertrophy is at least partly attributable to increases in the number of

sarcomeres (Alway et al., 1989; Gollnick et al., 1981; McDonnagh & Davies,

1984), increases in the number of those sarcomeres at optimum length might

occur in certain regions of muscle with RT. Therefore, the recruitment of

motor units within a muscle seems not only contingent on the ‘size principle’

(Milner-Brown et al., 1973), type of contraction (Person & Kudina, 1970) and

sensory input (Garnett & Stephens, 1981; Grimby & Hannerz, 1974;

Romanguére et al., 1992) but on their spatial location within the muscle.

It is likely then that the recruitment of functional compartments is related to the

length of sarcomeres in the muscle fibres. Van Zuylen et al. (1988) found that

the recruitment of these compartments was dependent on the joint angle, and

therefore the muscle length, at which a contraction was performed. Indeed,

Herring et al. (1984) found that sarcomere lengths varied between different

locations in the pig medial pterygoid, masseter and temporalis muscles. It is

therefore possible that functional compartments are organised on the basis of

the length-tension relationships of a fibre’s constituent sarcomeres. Strength

training using a particular movement pattern or joint angle could stimulate

changes in sarcomere length within the functional compartment which was

most readily recruited for a given contraction. However, if changes also

occurred in those functional compartments that were not readily recruited,

sarcomeres in these latter compartments would then be of more similar length

at rest to those compartments that were readily recruited during the

contraction. They could therefore contribute more to subsequent

contractions. The increased muscle activity in these regions could result in

greater EMG during a given contraction at all contraction strengths since more

fibres would be recruited at low levels of force and the firing rates at

subsequently greater contraction strengths would be higher. However these

increases would only be seen if a surface electrode was placed close to the

site of increased muscle activation. The areas over which functional

compartments span would possibly also change since some compartments

189

may become homonymous with others.

8.1.6 How does muscle strength increase in a velocity-specific manner?

Most increases in movement velocity have been attributed to increases in

fast-twitch fibre size or content. This makes intuitive sense since fast-twitch

fibres have higher contraction velocities than slow-twitch fibres. However,

other muscle properties can affect its velocity characteristics. Longer fibres

have been theoretically and experimentally shown to exhibit greater

shortening velocities (Burkholder et al., 1994; Sacks & Roy, 1982; Wickiewicz

et al., 1984). Furthermore, longer fibres are prevalent in fibres that often

perform higher-velocity, low-force contractions (Van Eijden et al., 1997), and

in muscles of well-trained sprint athletes (Kumagai et al., 2000). Fibre

lengthening occurs by an increase in the number, but decrease in the length

of sarcomeres (Matano et al., 1994; Williams, 1990). While it is unclear how

quickly these changes proceed in humans, they have been shown within

hours of a stretch stimulus in animals (Williams, 1990). In the present thesis

fibre length changes occurred within weeks.

The total length change of a contracting fibre equals the sum of shortening of

individual sarcomeres. Therefore, the more sarcomeres arranged in series,

the greater propensity for fibre length change. Since velocity is determined by

the length change per unit time, small displacements in each sarcomere

would culminate in large fibre length changes in a given amount of time. Thus

shortening velocity would be great. In addition, sarcomeres could shorten

less, and maintain lengths around optimum more often, if more are arranged

in series. Thus the force involved would be increased and power (dictated by

both the force and velocity of the contraction) would be greater.

8.1.7 What about conflicts in architecture and fibre type?

While fibre type changes should parallel architecture changes this is not often

190

the case. For example, the gastrocnemius muscle is characterised by large

pennation angles, short fibres and a high fast-twitch fibre percentage.

Furthermore, Burkholder et al. (1994) found a poor correlation between fibre

length and slow-twitch fibre percentage in human muscles. Why is it that a

muscle can have architecture conducive to slow-velocity, high force

production, but fibre type preponderance consistent with muscles that

produce fast force?

Perhaps fibre type is dependent more on metabolic and velocity constraints

whereas architecture is dependent more on force requirements. Fast-twitch

fibre content is highly correlated with performance in tasks requiring fast force

production (Coyle et al., 1979; Froese & Houston, 1985; Suter et al., 1993).

Their shorter half-relaxation times might also be a benefit in rapid eccentric

contractions where sarcomere elongation is required. Finally, they have a

better anaerobic capacity than slow-twitch fibres. The gastrocnemius is often

used in jumping movements where high forces are necessary, but small

amplitude rapid movements are required. Furthermore, the highly anaerobic

nature of fast-twitch fibres are useful given the muscle rarely participates in

endurance-type exercise. As an added benefit, the improved anaerobic

capacity of fast-twitch fibres might be more important in pennate muscles

where higher intra-muscular pressures could impede blood flow (Van

Leeuwen & Spoor, 1994). Increases in pennation however are usually

proportional to increases in the force production of a muscle (Benninghoff &

Rollhauser, 1952; Wottiez et al., 1983) or inversely related to fibre length

(Burkholder et al., 1994). Also, strength increases seem related to changes in

pennation, but not necessarily hypertrophy (Blazevich & Giorgi, 2001;

Blazevich et al., 1998; Henriksson-Larsén et al., 1992). So the relationship

between muscle pennation, fibre length and fibre type is complex and

probably determined by the force, velocity and metabolic requirements of a

muscle.

191

8.1.8 Conclusion

The purpose of this section of the thesis was to provide evidence for the

hypothesis that changes at the muscle level, or within some regions of

muscle, can result in increases in strength without noticeable increases in

muscle activation or muscle size. Should changes in sarcomere length occur

with RT, adaptations to strength would include specific increases in strength

at the joint angle at which maximum force was exerted during training and

therefore predicts that strength increases should be task specific.

8.2 ‘PERIPHERAL ADAPTATIONS’ EXAMPLE OF STRENGTH CHANGES

AFTER RESISTANCE EXERCISE.

Any model used to explain neuromuscular changes to training (particularly

resistance training in this instance) must predict several outcomes. These

include the following:

1. Muscle activation changes should increase with strength changes,

although, since this does not occur in many cases, strength increases

should not be dependent on increases in muscle activation.

2. Strength increases must be obtainable without a marked increased in

twitch or tetanic force (i.e. level of muscle activation).

3. Early increases in muscle size should not be detectable by ultrasound or

MRI techniques.

4. Changes in strength must be specific to the muscle lengths or joint angles

used in training.

5. Angle-specific strength improvements should not occur with a decrease in

force at non-training angles, but rather little or no increase at those angles.

6. Changes in strength must be specific to the body position or posture used

in training.

7. Changes in strength must be specific to the velocity of the training

192

exercises without changes in muscle activation.

8. Significant cross-education effects must be possible after unilateral

training.

9. Large increases in strength must be obtainable within the first few weeks

of training, but smaller increases should be seen thereafter.

In order to explain such an adaptive process, a fictional muscle (FM) will be

chosen as the subject of the model. It will be unipennate and able to perform

two functions, flexion and rotation. It will have a proportion of motor units

(MU’s) that are recruited mostly for flexion tasks (medial portion) and others

recruited mostly for rotation (lateral portion). Muscle fibres that are central will

tend to be activated easily during both tasks, but are not recruited for low level

force production. Thus FM is similar in function to the biceps brachii (Ter Haar

Romeny et al., 1984). 60% of its fibres will be fast-twitch and 40% slow

twitch. Furthermore, its original position of greatest strength will be with a

joint angle of 90o. Flexor training of the right limb will be performed at a slow

(15o.s-1) velocity through the range of 0o – 60o (full range of motion = 0o to

1700) of elbow flexion three times a week for eight weeks. Long rest periods

will separate three sets of 6 repetitions of exercise training.

8.2.1 What adaptations are likely in the first week of training?

Sarcomeres seem to adapt such that optimum overlap exists at muscle

lengths where high forces are commonly produced. Based on the evidence

presented previously, one might expect that an increase in sarcomere number

and decrease in length would occur with the process beginning after the first

session and predominate early in the training weeks. Consequently there

would be a change in the functional length-tension characteristics of FM

fibres. Since sarcomere lengths are not uniform throughout the muscle one

might also expect that fibres would adapt such that more sarcomeres with

ideal length-tension characteristics for the exercises are available within the

muscle. However, those sarcomeres near optimum length for elbow flexion

193

through this range of motion would have been most maximally recruited.

Even during maximal contractions sarcomeres at extreme (short or long)

muscle lengths would contribute little to the overall muscle force. Indeed

fibres on their descending limb would probably lengthen maximally and

provide passive tension and aid force transmission.

Therefore, it would most likely be that sarcomeres that were close to optimum

length when working through the training range of motion (in this example

these would probably be the centrally-located motor units that are active

during both low-level rotation and flexion) would adapt first. This would occur

with no change in neural pathways initially, however the body might soon

adapt to the new distribution of fibres with changes to the innervation of

muscle. Consequently, the number of motor units activated during low-force

flexion contractions would increase and, approaching maximum, the firing rate

of those motor units would be greater given their early recruitment. In this

case, the change in the number of fibres that are at an ideal length would

increase and be reflected in greater EMG detected at surface electrodes.

However, since only a small portion of closely-grouped MU’s would have

greater activity, changes in EMG would be small, and probably not detected

unless the electrode/s was/were placed immediately over the MU group.

If the theory previously presented is true then in multifunctional muscles the

area over which motor units are readily recruited during the task being trained

should increase if the other training is not being performed concurrently.

Indeed, Tonndorf and Hannam (1994) found some motor unit territories

crossed the intramuscular tendons that typically separated functional

compartments within the human masseter. Does this provide evidence that

motor unit territories were expanding? The model also predicts of course that

training while the muscle is in a lengthened position will culminate in fibre

length-tension changes that are ideal for working at long lengths, especially in

those motor units which are most readily recruited.

194

Similarly, the theory also explains why increases in EMG are not always

seen after periods of strength training. Since only some areas of muscle will

contain sarcomeres at, or near, optimum length for a given contraction, other

sarcomeres must be either too short or too long. Sarcomeres that are too

long are said to be on the ‘descending limb’ of their length-force curve.

Research by Morgan (1990; although tentatively refuted by Allinger et al.

[1996]) has shown that such sarcomeres might lengthen to their physiological

maximum. At this length they provide only passive tension created by their

elastic structures. There would be no requirement for activation of these

sarcomeres. Thus EMG electrodes placed on the muscle around areas

where sarcomeres tended to their physiological maximum may not record

signals that represent total muscle activity. Thus one difference between

those studies that showed increases in EMG after training and those that did

not may be the positioning of electrodes over the muscle. Multiple electrode

arrays (see Chanaud et al., 1991; Thusneyapan & Zahalak, 1989) may

therefore be more useful in gauging muscle activity changes after training.

It is possible also that hypertrophy of fibres (increases in contractile and

connective tissues) that are most active would occur rapidly. This might

parallel decreases in intra-muscular fat deposits and increases in the radial

packing density of contractile tissue. As such, increases in overall muscle

thickness, cross-section or volume would not be seen. Furthermore, early

hypertrophy might be confined only to those areas where sarcomeres are

near optimum length. Selective hypertrophy has been shown after RT (Housh

et al., 1992; Narici et al., 1996) and there was good evidence that it may have

occurred in Study Five of the present thesis. Nonetheless, if as presented

above joint-angle specific changes occur largely by sarcomere length

changes one could speculate that not only would a muscle become stronger

at one muscle length, but weaker at another. A more general hypertrophy of

the muscle would prevent such a decline at non-training angles.

Due to its unipennate fibre arrangement, increases in pennation would

195

contribute to strength increases in FM. It is possible that pennate muscles

have a greater propensity for early strength increases since increases in

pennation could occur simultaneously with other changes. Alternatively, the

increased pennation of such muscles might occur in place of other

adaptations. The increase in force production capability of pennate muscles

would then be the same as for parallel muscles. Fibre lengths would also

decrease, firstly because fibre shortening would reduce the volume of the

muscle after pennation had increased, thus allowing the muscle to remain a

size that easily fits into the compartment in which it sits. Also the decrease in

fibre length would increase force-generating capacity. The slow contractions

might induce some changes in fibre type, but since the muscle is rarely

performing contractions in an ischaemic state (i.e. many contractions at high

force with minimal rest) fibre type transition from its current proportions would

be unlikely.

Increases in the left (non-trained) FM might also occur. Generally, cross-

education has been attributed to neural causes. However changes at the

muscle level might occur. Srihari (1981) showed that myosin light chain

expression changed in a soleus muscle after cross-innervation of the

contralateral soleus with gastrocnemius. It was hypothesised that a neural

feedback mechanism was involved in this muscular adaptation. However it is

possible that, since messengers (namely hormones) stimulate protein

synthesis, a blood-borne messenger is responsible. Indeed increases in

blood flow to a non-training limb have been shown after unilateral training

(Yasuda & Miyamura, 1983). What if training of one muscle stimulated the

release of these messengers into the bloodstream? If these messengers

attached to particular receptors that differed between muscles, or differed

between sections of muscles, then muscular changes could occur without

intervention from the nervous system. Such a mechanism is purely

speculation, changes in muscle architecture of fibre properties have not been

investigated after unilateral training. The cause of the cross-education effect

therefore is unclear.

196

It must be added however that some early neural adaptations could occur.

Increases in synchronisation might enhance force production. Early changes

could at least partially explain the increase in surface EMG shown in some

studies (Yao et al., 2000). Also, a decrease in reflex inhibition in the first two

weeks of training would allow more motor units to contribute to force under

high loads. A reduced reflex inhibition however is most likely to be significant

in ‘untrained’ as apposed to ‘active’ or ‘well-trained’ subjects whose

neuromuscular systems would have experience in lifting heavy loads.

Nonetheless, early strength increases do not have to be mediated by a

‘reworking’ of neural pathways initially, but by muscular changes which occur

in response to the stresses placed on them.

8.2.2 What about muscle activation?

It is interesting to hypothesise why we often do not see a change in muscle

activation after training. First, studies which have examined sub-populations

of motor units (i.e. functional compartments) have reported some motor units

which are not activated during some tasks at low force levels (Ter Haar

Romeny et al., 1982, 1984; Van Zuylen et al., 1988). What if this is caused by

an inhibitory mechanism at the muscle level that could be controlled by neural

circuitry of the central nervous system. In this case, if muscle stimulation

could not activate these motor units during a maximum contraction, then

subjects may not be activating their muscles fully but muscle stimulation

would not allow any additional recruitment.

Should this be correct, increases in force after stimulation would be ascribed

to subjects not providing maximum effort prior to stimulation or subjects

learning how to involve all possible muscles for that specific task. After task

training, the number of motor units containing fibres of ideal length for that

contraction would increase. The inhibitory mechanism at the muscle level

would then be switched off to allow those extra motor units to be recruited

197

early. There may still be other motor units that cannot be activated.

Therefore, even though more of the muscle can be activated during a given

contraction. Electrical stimulation still might not recruit any more muscle than

is already activated during the voluntary contraction unless the subject failed

to attain maximum effort or they had not learned to produce maximum force.

Or perhaps those extra motor units are unable to significantly increase the

force of contraction since they are not near optimum length. Therefore, after

training the muscle force will improve and muscle activity would increase, but

muscle stimulation will only produce greater gains in force if the subject was

not providing a maximal contraction prior to stimulation. Again, this is purely

speculation.

Alternatively, the failure of electrical stimulation techniques to increase muscle

force might be related to the length of sarcomeres during maximal

contractions. As described earlier, sarcomeres that are at longer-than-

optimum lengthen further to their physiological maximum and exert passive

force during maximal muscle contractions. The provision of electrical

impulses to the muscle may still not allow these sarcomeres to contract since

their actin-myosin overlap would not allow sufficient force to be produced.

Those sarcomeres that are at, or are less than, optimum may always be more

readily recruited. Thus increases in muscle force with training may occur

when fewer sarcomeres lengthen to their physiological maximum, or when the

sarcomeres at or near optimum increase their force generating capacity. The

response to resistance training, particularly angle-specific adaptations to

resistance training, may reflect the number of sarcomeres at or near optimum

for a movement of given characteristics.

8.2.3 What about general strength increases?

Since adaptations to the sarcomeres, and therefore the muscle

compartments, is specific to the training task, increases in strength will not be

likely in an unassociated task. This is generally shown in past studies

198

(Abernethy & Jürimäe, 1994; Lindh, 1979; Rutherford et al., 1986; Thépaut-

Mathieu et al., 1988; Weir et al., 1995b). Unfortunately, no research has

examined the activation of compartments during maximal contractions to

determine if compartments that remain inactive during a particular task

become active at maximum.

8.2.4 Long-term adaptations?

Several processes could mediate longer-term improvements in strength.

First, the working muscle will be better able to cope with the loads imposed on

it such that eventually muscle damage and breakdown are of smaller

magnitude and protein synthesis can more dramatically outweigh it. As such,

increases in muscle size would be more rapid. This greater muscle

hypertrophy would lead to improved muscle strength. Also, the nervous

system would continue to adapt to the ‘new’ muscle state acquired from

training. Inter- and intra-muscular coordination would be enhanced so that

certain muscles within a group would be recruited before others thus

amplifying both angle-specific and body position- or posture-specific training

adaptations. Indeed one would ‘learn’ how to most effectively use the muscle

that has changed since training began. Importantly, by providing the muscle

with several stimuli (i.e. concurrent training) the adaptive process would be

more complex and clear changes would not be as readily seen. Such a result

was clearly observed in the present thesis. The processes outlined above

can be summarised as in Figure 8.1.

8.3 SUMMARY

Changes in neural pathways may not adequately predict early increases in

strength with RT. However many adaptations within the muscular system can

account for research observations well. These include changes in sarcomere

lengths and number, architectural changes and fibre hypertrophy (without total

muscle size increases). Neural adaptations may be secondary to these

199

muscular changes while long-term strength changes might be a result of

continued hypertrophy and more minor neural adaptations.

Visible hypertrophy

Fibre hypertrophyPennation & fibre length

Sarcomere adaptation

Inter- and intra-muscular coordination

Synchronisation/inhibitory reflex

0 1 2 3 4 5 6 7 8

Week of Training

0 1 2 3 4 5 6 7 8

Week of Training

50

10

0%

Rat

e of

Cha

nge

Rel

ativ

eto

Max

imum

50

10

0%

A

BFigure 8.1. Hypothesised time course of muscular (A) and neural (B) changes with resistance exercise.Many of the early changes (<2 weeks) might result from muscular adaptations with changes in thenervous system promptly following. Long-term (>6 weeks) adaptations might occur from considerablehypertrophy and continuing neural adaptation. Different muscles (i.e. different size, architecture, action,etc.) would respond differently, the model presented here is theoretical and may not be faithful to the timecourse f change.

B

A

200

CCHHAAPPTTEERR 99:: TTHHEESSIISS

SSUUMMMMAARRYY

201

9.1 SUMMARY

The first study examined the movement patterns of several resistance and

performance tasks in order to describe similarities between them. The results

were that the VJ without arm swing (particularly with arms placed across the

chest) was kinematically similar to the jump squat exercises. The traditional,

slower squat lift however was not similar largely because joint angle changes

occurred simultaneously rather than sequentially. Also, none of the broad

jump variations were similar to the FHS. Nonetheless the acceleration phase

of sprint running, as described by Jacobs and Ingen Schenau (1992) did

appear similar in both the magnitude and timing of joint angle changes to the

FHS. Given that the FHS is performed in a semi-prone position and can be

performed unilaterally, one could consider the pushing phases of these two

movements very similar. A kinematic study investigating the movement

patterns of subjects performing both tasks is required to more clearly establish

their similarity.

Although two groups of tasks (VJ with arms across the chest and jump-squat,

and the FHS and acceleration phase of a sprint run) were found to be

kinematically similar, it was unclear if they could be described as functionally

(kinetically) similar. That is, do subjects who perform well in a resistance task

also perform well in its related performance task? It is possible that for

optimum improvements in a performance task to occur, the resistance task

might have to be both kinematically and functionally similar. Results of Study

Four included a strong relationship existed between ISQ and VJ performance,

but not JSQ and VJ performance. This suggested that JSQ, while being

kinematically similar, was not functionally similar. The similarity between ISQ

and VJ may reflect their requirement for high muscle forces/stiffness at long

muscle lengths. In the VJ, high muscle forces/stiffness may be required for

optimum use of the stretch-shorten cycle. There was however a strong

relationship between the FHS and acceleration phase of a sprint run.

Furthermore, component analysis hinted at a similarity in their force-velocity

202

characteristics. As such the FHS and sprint tasks could be considered

both kinematically and functionally similar. Given the results of this fourth

study, it was deemed possible to test the effects of kinematic and functional

similarity on performance adaptations in the third study.

The purpose of the fifth study was to examine changes in SQ, FHS, sprint and

VJ performance after a short period of either concurrent resistance- and

sprint/jump training or sprint/jump training alone. Further, the effect of

movement pattern of RT exercises could be compared by two of the

resistance groups performing tasks with different movement patterns as their

dominant training exercise. After five weeks of training there was no

difference between the groups in squat, FHS, sprint or VJ performance.

Therefore, short duration, concurrent training appeared to have no significant

movement pattern- or velocity-specific effects in well-trained subjects. It was

also not possible therefore to determine if only kinematic similarity, or both

kinematic and functional similarity, was required between resistance and

performance tasks for optimum improvements in a task to occur. The low

statistical power resulting from low subject numbers may have affected

significant findings. However, if clear differences existed between groups,

these would have likely been detected since statistically significant

improvements in many of the resistance and task tests were found across the

groups after the five weeks of training.

Many factors affect the movement pattern-specific effect. Three of these were

examined in this fifth study: body position, joint angle and laterality. There

was no apparent effect of body position on training adaptations as there was

no difference between the resistance groups in their performance of the FHS

and squat tests. Although the magnitude and timing of joint angle changes

and laterality also differed between these two tasks, one would expect that if

body position affected performance then some differences between groups

would have been found given they trained with exercises that had different

body positions. On the other hand, a difference between the groups would

203

not have been conclusive evidence of an effect of body position given the

other factors that differed between the tasks.

With respect to joint angle changes, while the timing and magnitude of joint

angle changes differed between the SQ and FHS tasks, there were no

differences between the groups that trained with these tasks. Nonetheless,

there was some evidence (supported by high effect sizes) of between-group

differences in the angle at which peak torque was produced (APT) during slow

isokinetic knee extension. APT in subjects who performed SQ training was

produced at a more closed angle after training while there was no difference

in the angle for subjects who trained with the FHS. Given that the range of

motion through which the knee moved was greater for subjects who

performed the SQ training, the result provides some evidence for angle-

specific torque changes. If small changes in APT did occur between groups,

between-group differences in dynamic tests could possibly be expected after

longer training periods.

Effects of laterality of training were also investigated. There was no evidence

for laterality-specific adaptations as there were no differences in unilateral VJ,

unilateral FHS or unilateral isokinetic knee extension performance after

training. Again, the result might be due to the short training period and/or low

subject number. Alternatively the result might suggest that early adaptations

to concurrent strength and sprint/jump training are not specific to the laterality

of training exercises.

The effects of training velocity could be examined since one group performed

no RT and therefore performed only high-speed running and jumping

movements. There was strong evidence that muscle pennation of the vastus

lateralis muscle increased while fascicle length decreased in groups who

performed RT in addition to the sprint/jump training. Subjects who performed

no RT however showed no increase in pennation but longer fascicle lengths.

Such changes may have contributed to similar increases in muscle thickness

204

after training. The changes were certainly similar to those described

previously in the literature (Burkholder et al., 1994; Kawakami et al., 1995).

Nonetheless, these architectural changes, while theoretically important to the

shortening velocity of the muscle, did not manifest themselves by changes in

dynamic performance in this short-term study. There was no difference

between groups in the performance of the SQ, FHS, sprint or jump tests, nor

was there a difference in their improvements in isokinetic knee extensor

torque at any movement speed (30o.s-1 or 180o.s-1). The lack of significant

change in the knee extension test might be due to the training and testing

modes being different. However, the change in architectural characteristics of

muscle suggest that long-term training, even when resistance- and task

training are performed concurrently, might result in velocity-specific

performance changes. Given that changes occur rapidly however, athletes

who use resistance- and task training concurrently might be able to quickly

reverse any adverse architectural changes by performing only sprint-type

training.

Finally, the results of the EMG analyses were equivocal due to high inter-

individual variability and low statistical power. There was some evidence

however that changes in muscle activity of resistance-trained subjects may

have affected sprint running but improved VJ efficiency. However there was

no change in muscle co-contraction patterns in sprint running or in the muscle

activity onset times during VJ. There were also no changes in the muscle

activity patterns of sprint/jump subjects. As such, changes in the nervous

system may be highly individual, especially when resistance- and task training

are performed concurrently by well-trained subjects for short periods and

changes in the nervous system resulting from training may not be as

consistent as when RT is performed in isolation.

In conclusion, for the subjects tested here there was some evidence of

muscle architectural changes related to the velocity of training exercises.

However there were no differences between the groups in their performance

205

of SQ, FHS, sprint or VJ tests, and little or no change in joint angle-specific

torque at the knee or muscle activity patterns. Therefore, for short training

periods, changes resulting from concurrent training appear different to those

where RT is performed in isolation in that changes are not as abrupt or

consistent across subjects. Nonetheless, there is enough evidence to

suggest that differences between ‘specific’ and ‘non-specific’ training may be

significant after longer training periods.

9.2 FUTURE RESEARCH

There are many neuromuscular adaptations that can occur with RT and with

concurrent training. Certainly there is still much work needed to ascertain the

exact nature of these adaptations. This work been highlighted throughout the

thesis and will not be reiterated here. Some important research that must be

conducted however stems from limitations of Study Five. Namely:

1) changes in muscle activation need to be examined in greater detail,

2) more subjects are required to provide a more detailed and accurate

account of neuromuscular and performance changes,

3) training should be performed for longer (> 3 months) periods to allow

examination of both short- and long-term adaptations to the training.

4) Different concurrent training regimes need to be used in studies to assess

the effects of relative volumes and intensities of resistance- and task

training.

Such research, combined with more detailed research investigating singular

mechanisms would improve our knowledge of adaptations to concurrent

resistance- and speed training and help coaches and athletes plan their

training for optimum performance.

206

RREEFFEERREENNCCEESS

207

REFERENCES

1. Abe, T., Kumagai, K. & Brechue, W.F. (1999). Muscle fascicle length isgreater in sprinters than long-distance runners (Abstract). Medicine andScience in Sports and Exercise, 31 Suppl. 5: S328.

2. Abernethy, P., Wilson, G. & Logan, P. (1995). Strength and powerassessment: issues, controversies and challenges. Sports Medicine,19(6): 401-417.

3. Abernethy, P.J. & Jürimäe, J. (1996). Cross-sectional and longitudinaluses of isoinertial, isometric and isokinetic dynamometry. Medicine andScience in Sports and Exercise, 28(9): 1180-1187.

4. Abernethy, P.J., Jürimäe, J., Logan, P.A., Taylor, A.W. & Thayer, R.E.(1994). Acute and chronic response of skeletal muscle to resistanceexercise. Sports Medicine, 17(1): 22-38.

5. Adams, K., Hather, B.M, Baldwin, K.M. & Dudley, G.A. (1993). Skeletalmuscle myosin heavy chain composition and resistance training. Journalof Applied Physiology, 74(2): 911-915.

6. Adams, K., O’Shea, J.P., O’Shea, K.L. & Climstein, M. (1992). The effectof six weeks of squat, plyometric and squat-plyometric training on powerproduction. Journal of Applied Sport Science Research, 6(1): 36-41.

7. Agre, J.C., Magness, J.L., Hull, S.Z., Wright, K.C., Baxter, T.L., Patterson,R. & Stradel, L. (1987). Strength testing with a portable dynamometer:reliability for upper and lower extremities. Archives of Physical Medicineand Rehabilitation, 68(7): 454-458.

8. Aguado, X., Izquierdo, M. & Montesinos, J.L. (1997). Kinematic and kineticfactors related to the standing long jump performance. Journal of HumanMovement Studies, 32: 156-169.

9. Akima, H., Takahashi, H., Kuno, S.Y., Masuda, K., Masuda, T., Shimojo,H., Anno, I., Itai, Y. & Katsuta, S. (1999). Early phase adaptations ofmuscle use and strength to isokinetic training. Medicine & Science inSports & Exercise, 31(4): 588-594.

10. Alexander, M.J.L. (1990). Peak torque values for antagonist musclegroups and concentric and eccentric contraction types for elite sprinters.Archives of Physical Medicine and Rehabilitation, 71(5): 334-339.

208

11. Allen, G.M., Gandevia, S.C. & McKenzie, D.K. (1995). Reliability ofmeasurements of muscle strength and voluntary activation using twitchinterpolation. Muscle and Nerve, 18: 593-600.

12. Allinger, T.L., Epstein, M. & Herzog, W. (1996). Stability of muscle fiberson the descending limb of the force-length relation. A theoreticalconsideration. Journal of Biomechanics, 29(5): 627-633.

13. Almasbakk, B. & Hoff, J. (1996). Coordination, the determinant of velocityspecificity? Journal of Applied Physiology, 80(5): 2046-2052.

14. Alway, S.E., Grumbt, W.H, Gonyea, W.J. & Stray-Gundersen, J. (1989).Contasts in muscle and myofibers of elite male and female body builders.Journal of Applied Physiology, 67(1): 24 -31.

15. Alway, S.E., Grumbt, W.H., Stray-Gundersen, J. & Gonyea, W.J. (1992).Effects of resistance training on elbow flexors of highly competitivebodybuilders. Journal of Applied Physiology, 72(4): 1512-1521.

16. Andersen, J.L., Klitgaard, H. & Saltin, B. (1994). Myosin heavy chainisoforms in single fibres from m. vastus lateralis of sprinters: influence oftraining. Acta Physiologica Scandinavica, 151: 135-142.

17. Aoki, H., Tsukahara, R. & Yabe, K. (1989). Effects of pre-motionelectromyographic silent period on dynamic force exertion during a rapidballistic movement in man. European Journal of Applied Physiology andOccupational Physiology, 58(4): 426-432.

18. Arnold, B.L. & Perrin, D.H. (1993). The reliability of four different methodsof calculating quadriceps peak torque and angle-specific torques at 30o,60o, and 75o. Journal of Sport Rehabilitation, 2: 243-250.

19. Asmussen, E. & Bonde-Petersen, F. (1974). Storage of elastic energy inskeletal muscles in man. Acta Physiological Scandinavica, 91: 385-392.

20. Ausoni, S., Gorza, L., Schiaffino, S., Gundersen, K. & Lomo, T. (1990).Expression of myosin heavy chain isoforms in stimulated fast and slow ratmuscles. Journal of Neuroscience, 10(1): 153-160.

21. Baker, D., Wilson, G. & Carlyon, B. (1994). Generality versus specificity: acomparison of dynamic and isometric measures of strength and speed-strength. European Journal of Applied Physiology and OccupationalPhysiology, 68: 350-355.

209

22. Bandy, W.D. & Hanten, W.P. (1993). Changes in torque andelectromyographic activity of the quadriceps femoris muscles followingisometric training. Physical Therapy, 73(7): 455-467.

23. Bar, A., Simoneau, J.A. & Pette, D. (1989). Altered expression of myosinlight-chain isoforms in chronically stimulated fast-twitch muscle of the rat.European Journal of Biochemistry, 178(3): 591-594.

24. Bárány, M. (1967). ATPase activity of myosin correlated with speed ofmuscle shortening. Journal of General Physiology, 50: 197-216.

25. Baratta, R., Solomonow, M., Zhou, B., Letson, D. & Chouinard, L. (1988).Muscular coactivation: The role of the antagonist musculature inmaintaining knee stability. American Journal of Sports Medicine, 16: 113-122.

26. Barkhaus, P.E. & Nandedkar, S.D. (1994). Recording characteristics of thesurface EMG electrodes. Muscle and Nerve, 17: 1317-1323.

27. Barrett, B. (1962). The length and mode of termination of individualmuscle fibres in the human sartorius and posterior femoral muscles. ActaAnatomica, 48: 242-257.

28. Behm, D.G. (1991). An analysis of intermediate speed resistanceexercises for velocity-specific strength gains. Journal of Applied SportScience Research, 5(1): 1-5.

29. Behm, D.G. & Sale, D.G. (1993a). Intended rather than actual movementvelocity determines velocity-specific training response. Journal of AppliedPhysiology, 74(1): 359-368.

30. Behm, D.G. & Sale, D.G. (1993b). Velocity specificity of resistancetraining. Sports Medicine, 15(6): 374-388.

31. Behm, D.G. & St-Pierre, D.M.M. (1998). The effects of strength trainingand disuse on the mechanisms of fatigue. Sports Medicine, 25(3): 173-189.

32. Belanger, A.Y. & McComas, A.J. (1981). Extent of motor unit activationduring effort. Journal of Applied Physiology: Respiration, Environment, and

210

Exercise Physiology, 51: 1131-1135.

33. Belka, D. (1968). Comparison of dynamic, static and combination trainingon dominant wrist flexor muscles. Research Quarterly, 39: 241-250.

34. Bell, D.G. & Jacobs, I. (1990). Muscle fibre area, fibre type &capillarization in male and female body builders. Canadian Journal ofSport Sciences/Journal Canadien des Sciences du Sport 15(2): 115-119.

35. Bell, G.J. & Wenger, H.A. (1992). Physiological adaptations to velocity-controlled resistance training. Sports Medicine, 13(4): 234-244.

36. Bell, G.J., Petersen, S.R., Quinney, H. & Wenger, H.A. (1989). The effectof velocity-specific strength training on peak torque and anaerobic rowingpower. Journal of Sports Sciences, 7(3): 205-214.

37. Bellemare, F., Woods, J.J., Johansson, R. & Bigland-Ritchie, B. (1983)Motor-unit discharge rates in maximal voluntary contractions of threehuman muscles. Journal of Neurophysiology, 50(6): 1380-1392.

38. Bemben, M.G., Massey, B.H., Boileau, R.A. & Misner, J.E. (1992).Reliability of isometric force-time curve parameters for men aged 20 to 79years. Journal of Applied Sports Science Research, 6(3): 158-164.

39. Benninghoff, A. & Rollhauser (1952). Zur inneren Mechanik desgefiederten Muskels. Pflugers Archives, 254: 527-548.

40. Blazevich, A.J. (1995). The difference between seven-week ‘strength’ and‘speed’ resistance training programs on the performance of sprint runningathletes during concurrent resistance- and sprint-running training.Honours Thesis, The University of Queensland.

41. Blazevich, A.J. & Gill, N.D. (2001). Reliability and validity of two isometricsquat tests. Journal of Strength and Conditioning Research, In Press.

42. Blazevich, A.J. & Giorgi, A. (2001). Effect of testosterone administrationand weight training on muscle architecture. Medicine and Science inSports and Exercise, In Press.

43. Blazevich, A.J. & Jenkins, D. (1997). Physical performance differencesbetween weight-trained sprinters and weight trainers. Journal of Science

211

and Medicine in Sport, 1(1): 12-21.

44. Blazevich, A.J., Giorgi, A. & Murphy, P. (1998). The effect of 12 weeks ofresistance training on the relationship between muscle size and pennation.Australian Conference of Science and Medicine in Sport, AdelaideAustralia, 1998.

45. Blazevich, A.J., Newton, R.U., Sharman, M., Bronks, R. & Gill, N. (2000).Specificity of Strength training exercises to the vertical jump and 20 msprint tests. Australian and New Zealand Society of BiomechanicsConference. Gold Coast Australia. January 2000.

46. Bobbert, M.F., Mackay, M., Schinkelshoek, D., Huijing, P.A. & IngenSchenau, G.J. van. (1986). Biomechanical analysis of drop andcountermovement jumps. European Journal of Applied Physiology, 54:566-573.

47. Bobbert, M.F. & Van Soest, A.J. (1994). Effects of muscle strengtheningon vertical jump height: a simulation study. Medicine and Science inSports and Exercise. 26(8): 1012-1020.

48. Bobbert, M.F., Gerritsen, K.G.M., Litjens, M.C.A. & van Soest, A.J. (1996).Why is countermovement jump height greater than squat jump height?Medicine and Science in Sports and Exercise, 28(11): 1402-1412.

49. Booth, J., McKenna, M.J., Ruell, P.A., Gwinn, T.H., Davis, G.M.,Thompson, M.W., Harmer, A.R., Hunter, S.K. & Sutton, J.R. (1997).Impaired calcium pump function does not slow relaxation in humanskeletal muscle after prolonged exercise. Journal of Applied Physiology,83(2): 511-521.

50. Bottinelli, R. Schiaffino, S. & Reggiani, C. (1991). Force-velocity relationsand myosin heavy chain isoform composition of skinned fibres from rateskeletal muscle. Journal of Physiology, 437: 655-672.

51. Bottinelli, R., Canepari, M., Pellegrino, M.A. & Reggiani, C. (1996). Force-velocity properties of human skeletal muscle fibres: myosin heavy chainisoform and temperature dependence. Journal of Physiology, 495: 573-586.

52. Bottinelli, R., Sandoli, D., Canepari, M. & Reggiani, C. (1992). Maximalisometric force and myosin heavy chain isoform composition in single

212

skinned skeletal muscle fibres from the rat. European Journal ofPhysiology, 420: R193.

53. Brown, A.B., McCartney, N. & Sale, D.G. (1990). Positive adaptations toweight-lifting training in the elderly. Journal of Applied Physiology, 69(5):1735-1733.

54. Buchanan, T.S. & Lloyd, D.G. (1997). Muscle activation at the human kneeduring isometric flexion-extension and varus-valgus loads. Journal ofOrthopaedic Research, 15(1):11-17.

55. Buchanan, T.S., Almdale, P.J., Lewis, J.L. & Zev Rymer, W. (1986).Characteristics of synergic relations during isometric contractions ofhuman elbow muscles. Journal of Neurophysiology, 56(5): 1225-1241.

56. Buchanan, T.S., Rovai, G.P. & Zev Rymer, W. (1989). Strategies formuscle activation during isometric torque generation at the human elbow.Journal of Neurophysiology, 62(6): 1201-1212.

57. Burgess-Limerick, R., Abernethy, B. & Neal, R.J. (1993). Relative phasequantifies interjoint coordination. Journal of Biomechanics, 26(1): 91-94.

58. Burke, R.E. (1991). Selective recruitment of motor units. In: Motor Control:Concepts and Issues, Humphrey, D.R. & Freund, H.-J. (Eds), John Wiley& Sons Ltd., New York, pp. 5-21.

59. Burkholder, T.J., Fingado, B., Baron, S. & Lieber, R.L. (1994). Relationshipbetween muscle fiber types and sizes and muscle architectural propertiesin the mouse hindlimb. Journal of Morphology, 221: 177-190.

60. Cabric, M. & Appell, H.J. (1987). Effect of electrical stimulation of high andlow frequency on maximum isometric force and some morphologicalcharacteristics in men. International journal of sports medicine, 8(4): 256-260.

61. Cabric, M., Appell, H.-J. & Resic, A. (1988). Fine structural changes inelectrostimulated human skeletal muscle: evidence for predominant effectson fast muscle fibres. European Journal of Applied Physiology andOccupational Physiology, 57(1): 1-5.

62. Cadefau, J., Casademont, J., Grau, J.M., Fernandez, J., Balaguer, A.,

213

Vernet, M., Cusso, R. & Urbano-Marquez, A. (1990). Biochemical andhistochemical adaptation to sprint training in young athletes. ActaPhysiologica Scandinavica, 140(3): 341-351.

63. Cafarelli, E. & Fowler, B. (1993). Does maximal neural activation of muscleincrease after resistance training? European Journal of Applied Physiologyand Occupational Physiology, 66(6): 553-554.

64. Caiozzo, J., Perrine, T. & Edgerton, V.R. (1981). Training inducedalterations in the in-vivo force-velocity relationship of human muscle.Journal of Applied Physiology, 51: 750-754.

65. Canavan, P.K., Garrett, G.E. & Armstrong, L.E. (1996). Kinematic andkinetic relationships between an Olympic-style lift and the vertical jump.Journal of Strength and Conditioning Research, 10(2): 127-130.

66. Cannon, R.J. & Cafarelli, E. (1987). Neuromuscular adaptations totraining. Journal of Applied Physiology, 63(6): 2396-2402.

67. Carolan, B. & Cafarelli, E. (1992). Adaptations in coactivation afterisometric resistance training. Journal of Applied Physiology, 73(3): 911-1017.

68. Carroll, T.J., Abernethy, P.J., Logan, P.A., Barber, M. & McEniery, M.T.(1998). Resistance training frequency: strength and myosin heavy chainresponses to two and three bouts per week. European Journal of AppliedPhysiology and Occupational Physiology, 78(3): 270-275.

69. Chanaud, C.M, Pratt, C.A. & Loeb, G.E. (1987). A multiple-contact EMGrecording array for mapping single motor unit territories. Journal ofNeuroscience Methods, 21: 105-112.

70. Chanaud, C.M., Pratt, C.A. & Loeb, G.E. (1991). Functionally complexmuscles of the cat hindlimb. V. The roles of histochemical fiber-typeregionalization and mechanical heterogeneity in differential muscleactivation. Experimental Brain Research, 85: 300-313.

71. Chesley, A., MacDougall, J.D., Tarnopolsky, M.A., Atkinson, S.A. & Smith,K. (1992). Changes in human muscle protein synthesis after resistanceexercise. Journal of Applied Physiology, 73(4): 1383-1388.

214

72. Claassen, H., Gerber, C., Hoppeler, H., Luthi, J.M. & Vock, P. (1989).Muscle filament spacing and short-term heavy-resistance exercise inhumans. Journal of Physiology, 409: 491-495.

73. Clamann, H.P. & Schelhorn, T.B. (1988). Nonlinear force addition ofnewly recruited motor units in the cat hindlimb. Muscle & Nerve, 11(10):1079-1089.

74. Cohen, J. (1988). Statistical power for the behavioural sciences (2nd ed.).Lawrence Erlbaum Associates, New Jersey.

75. Colliander, E. & Tesch, P. (1990). Responses to eccentric and concentricresistance training in females and males. Acta Physiologica Scandinavica,141: 149-156.

76. Conrad, B., Benecke, R. & Goehmann, M. (1983). Premovement silentperiod in fast movement initiation. Experimental Brain Research, 51(2):310-313.

77. Cooke, J.D. & Brown, S.H. (1990). Movement related phasic muscleactivation II: generation and functional role of the triphasic pattern. Journalof Neurophysiology, 63: 465-472.

78. Costill, D.L., Coyle, E.F., Fink, W.F., Lesmes, G.R. & Witzmann, F.A.(1979). Adaptations in skeletal muscle following strength training. Journalof Applied Physiology, 46: 96-99.

79. Coyle, E.F., Coyle, D.L. & Lesmes, G.R. (1979). Leg extension power andmuscle fiber composition. Medicine and Science in Sports and Exercise,11: 12-15.

80. Coyle, E.F., Cote, R.W., Feiring, D.C., Roby, F.B. & Rotkis, T.C. (1981).Specificity of power improvements through slow and fast isokinetictraining. Journal of Applied Physiology: Respiratory, Environmental andExercise Physiology, 51(6): 1437-1442.

81. Davies, C.T.M., Dooley, P., McDonagh, M.J.N. & White, M.J. (1985.Adaptations of mechanical properties of muscle to high force training inman. Journal of Physiology, 365: 277-284.

82. Davies, C.T.M. & Young, K. (1983). Effects of training at 30 and 100%

215

maximal isometric force (MVC) on cnotractile properties of the tricepssurae in man. Journal of Physiology, 336: 22-23P.

83. Dawson, B., Fitzsimons, M., Green, S., Goodman, C., Carey, M. & Cole,K. (1998). Changes in performance, muscle metabolites, enzymes andfibre types after short sprint training. European Journal of AppliedPhysiology, 78: 183-169.

84. Delecluse, C., Van Coppenolle, H., Willems, E., Van Leemputte, M., Diels,R. & Goris, M. (1995). Influence of high-resistance and high-velocitytraining on sprint performance. Medicine and Science in Sports andExercise, 27(8): 1203-1209.

85. De Luca, C.J., LeFever, R.S., McCue, M.P. & Xenakis, A.P. (1982).Behaviour of human motor units in different muscles during linearly varyingcontractions. Journal of Physiology, 329: 113-128.

86. Desmedt, J.E. (1981). The size principle of motoneuron recruitment inballistic or ramp voluntary contractions in man. In Desmedt, J.E. (ed).Progress in Clinical Neurophysiology, 9: 97-136.

87. Desmedt, J.E. & Godaux, E. (1977). Ballistic contractions in man:characteristic recruitment pattern of single motor units of the tibialisanterior muscle. Journal of Physiology, 264:673-693.

88. DeVries, H.A. (1968). Immediate and long term effects of exercise uponresting muscle action potential level. Journal of Sports Medicine andPhysical Fitness, 8(1):1-11.

89. Doherty, T.J. & Campagna, P.D. (1993). The effects of periodized velocity-specific resistance training on maximal and sustained force production inwomen. Journal of Sports Sciences, 11: 77-82.

90. Dowling, J.J. & Cardone, N. (1994). Relative cross-sectional areas ofupper and lower extremity muscles and implications for force prediction.International Journal of Sports Medicine, 15(8): 453-459.

91. Duchateau, J. & Hainaut, K. (1990). Effects of immobilization on contractileproperties, recruitment and firing rates of human motor units. Journal ofPhysiology, 422: 55-65.

216

92. Duchateau, J., Lebozec, S. & Hainaut, K. (1986). Contributions of slowand fast muscles of triceps surae to a cyclic movement. European Journalof Applied Physiology, 55: 476-481.

93. Duke, A.M. & Steele, D.S. (2000). Characteristics of phosphate-inducedCa2+ efflux from the SR in mechanically skinned rat skeletal muscle fibers.American Journal of Physiology, Cell Physiology, 278(1): C126-C135.

94. Duncan, P.W., Chandler, J.M., Cavanaugh, D.K., Johnson, K.R. &Buehler, A.G. (1989). Mode and speed specificity of eccentric andconcentric exercise training. Journal of Orthopaedic and Sports PhysicalTherapy, 11(2): 70-75.

95. Eloranta, V. (1994). Activity pattern of leg musculature during jumpingmovements. Journal of Human Movement Studies, 26: 113-130.

96. English, AW. & Weeks, O.L. (1987). An anatomical and functional analysisof cat biceps femoris and semitendinosus muscles. Journal of Morphology,191: 161-175.

97. Enoka, R.M. & Fuglevand, A.J. (1993). Neuromuscular basis of themaximum voluntary force capacity of muscle. In: Grabiner, M.D. (ed.),Current Issues in Biomechanics, Human Kinetics, Champaigne, IL, pp.215-235.

98. Enoka, R.M. (1988). Muscle strength and its development: Newperspectives. Sports Medicine, 6: 146-168.

99. Enoka, R.M. (1994). Neuromechanical Basis of Kinesiology. HumanKinetics, Champaign, Ill., pp. 131-133.

100. Enoka, R.M. (1997). Neural adaptations with chronic physical activity.Journal of Biomechanics, 30(5): 447-455.

101. Esbjörnsson Liljedahl, M., Holm, I., Sylven, C. & Jansson, E. (1996).Different responses of skeletal muscle following sprint training in men andwomen. European Journal of Applied Physiology, 74: 375-383.

102. Essén, B., Jansson, E., Henriksson, J., Taylor, A.W. & Saltin, B.(1975). Metabolic characteristics of fibre types in human skeletal muscle.

217

Acta Physiologica Scandinavica, 95: 153-165.

103. Ettema, G.J. & Huijing, P.A. (1994). Effects of distribution of musclefiber length on active length-force characteristics of rat gastrocnemiusmedialis. Anatomical Record, 239(4): 414-420.

104. Ewing, J.L., Wolfe, D.R., Rogers, M.A., Amundson, M.L. & Stull, G.A.(1990). Effects of velocity of isokinetic training on strength, power, andquadriceps muscle fibre characteristics. European Journal of AppliedPhysiology, 61: 159-162.

105. Fisher, M.J., Meyer, R.A., Adams, G.R., Foley, J.M. & Potchen, E.J.(1990). Direct relationship between proton T2 and exercise intensity inskeletal muscle MR images. Investigative Radiology, 25: 480-485.

106. Fleck, S.J. & Kramer, W.J. (1988). Resistance training: physiologicalresponses and adaptations (Part 2 of 4). Physician and Sports Medicine,16:108.

107. Fleckenstein, J.L., Watumull, D., McIntire, D.D., Bertocci, L.A., Chason,D.P. & Peshock, R.M. (1993). Muscle proton T2 relaxation times and workduring repetitive maximal voluntary exercise. Journal of AppliedPhysiology, 74(6): 2855-2859.

108. Freund, H.J., Büdingen, J.J. & Dietz, V. (1975). Activity of single motorunits from human forearm muscle during voluntary isometric contractions.Journal of Neurophysiology, 38: 933-946.

109. Froese, E.A. & Houston, M.E. (1985). Torque-velocity characteristicsand muscle fiber type in human vastus lateralis. Journal of AppliedPhysiology, 59: 309-314.

110. Fuglevand, A.J., Winter, D.A., Patla, A.E. & Stashuk, D. (1992).Detection of motor unit action potentials with surface electrodes: Influenceof electrode size and spacing. Biology and Cybernetics, 67: 143-154.

111. Fukunaga, T., Ichinose, Y., Ito, M., Kawakami, Y. & Fukashiro, S.(1997). Determination of fascicle length and pennation in a contractinghuman muscle in vivo. Journal of Applied Physiology, 82(1): 354-358.

112. Fukushiro, S., Komi, P.V., Jarvinen, M. and Miyashita, M. (1995). In

218

vivo achilles tendon loading during jumping in humans. EuropeanJournal of Applied Physiology, 71: 453-458.

113. Gandevia, S.C. & McKenzie, D.K. (1988). Activation of human musclesat short muscle lengths during maximal static efforts. Journal ofPhysiology, 407: 599-613.

114. Gandevia, S.C., Allen, G.M. & McKenzie, D.K. (1995). Central fatigue:Critical issues, quantification and practical implications, In S.C. Gandevia,R.M. Enoka, A.J. McComas, D.G. Stuart and C.K. Thomas (eds), Fatigue:Neural and Muscular Mechanisms. Plenum, New York, pp. 281-294.

115. Gardner, G.W. (1963). Specificity of strength changes of the exercisedand nonexercised limb following isometric training. Research Quarterly,34: 98-101.

116. Gareis, H., Solomonow, M, Baratta, R., Best, R. & D’Ambrosia, R.(1992). The isometric length-force models of nine different skeletalmuscles. Journal of Biomechanics, 25(8): 903-916.

117. Garfinkel, S. & Cafarelli, E. (1992). Relative changes in maximal force,EMG and muscle cross-sectional area after isometric training. Medicineand Science in Sports and Exercise, 24(11): 1220-1227.

118. Garnett, R. & Stephens, J.A. (1981). Changes in the recruitmentthreshold of motor units produced by cutaneous stimulation in man.Journal of Physiology, 311: 463-473.

119. Garnica, R.A. (1986). Muscular power in young women after slow andfast isokinetic training. Journal of Orthopaedic and Sports PhysicalTherapy, 8(1): 1-9.

120. Geiger, P.C., Cody, M.J. & Sieck, G.C. (1999). Force-calciumrelationship depends on myosin heavy chain and troponin isoforms in ratdiaphragm muscle fibers. Journal of Applied Physiology, 87(5): 1894-1900.

121. Gillard, D.M., Yakovenko, S, Cameron, T. & Prochazka. (2000).Isometric muscle length-tension curves do not predict angle-torque curvesof human wrist in continuous active movements. Journal of Biomechanics,33: 1341-1348.

219

122. Giorgi, A., Weatherby, R.P. & Murphy, P.W. (1999). Muscularstrength, body composition and health responses to the use ofTestosterone Enanthate: a double-blind study. Journal of Science andMedicine in Sport, 2(4): 325-339.

123. Goldspink, G., Tabary, J.C., Tabary, C., Tardieu, C. & Tardieu, G.(1974). Effect of denervation on the adaptation of sarcomere number andmuscle excitability to the functional length of muscle. Journal ofPhysiology, 236: 733-742.

124. Goldspink, G., Scutt, A., Martindale, J., Jaenicke, T.Turay, L & Gerlach,G-F. (1991). Stretch and force generation induce rapid hypertrophy andmyosin isoform gene switching in adult skeletal muscle. BiochemicalSociety Transactions, 19: 368-373.

125. Gollhoffer, A., Strojnik, V., Rapp, W. & Schweizer, L. (1992). Behaviourof triceps surae muscle-tendon complex in different jump conditions.European Journal of Applied Physiology, 64: 283-291.

126. Gollnick, P.D., Timson, B.F., Moore, R.L. & Riedy, M. (1981). Muscularenlargement and number of fibers in skeletal muscles of rats. Journal ofApplied Physiology, 50: 936-943.

127. Gonyea, W.J. Sale, D.G., Gonyea, F.B & Mikesky, A. (1986). Exerciseinduced increases in muscle fiber number. European Journal of AppliedPhysiology and Occupational Physiology, 55: 137-141.

128. Gorza, L., Gundersen, K., Lomo, T., Schiaffino, S. & Westgaard, R.H.(1988). Slow-to-fast transformation of denervated soleus muscles bychronic high-frequency stimulation in the rat. Journal of Physiology, 402:627-649.

129. Grange, R.W., Cory, C.R., Vandenboom, R. & Houston, M.E. (1995).Myosin phosphorylation augments the force-displacement and force-velocity relationships of mouse fast muscle. American Journal ofPhysiology, 269(Cell Physiology 38): C713-C724.

130. Grange, R.W., Vandenboom, R., Xeni, J. & Houston, M.E. (1998).Potentiation of in vitro concentric work in mouse fast muscle. Journal ofApplied Physiology, 84(1): 236-243.

131. Graves, J.E., Pollock, M.L., Jones, A.E., Colvin, A.B. & Leggett, S.H.

220

(1989). Specificity of limited range of motion variable resistancetraining. Medicine & Science in Sports & Exercise. 21(1): 84-89.

132. Green, H.J. (1992). Myofibrillar composition and mechanical function inmammalian skeletal muscle. Sciences Reviews, 1: 43-64.

133. Green, H.J., Grange, F., Chin, C., Goreham, C. & Ranney, D. (1998).Exercise-induced decreases in sarcoplasmic reticulum Ca2+-ATPaseactivity attenuated by high-resistance training. Acta PhysiologicaScandinavica, 164(2): 141-146.

134. Gregor, R.J., Cavanagh, P.R. & LaFortune, M. (1985). Knee flexormoments during propulsion in cycling - A creative solution to Lombard'sParadox. Journal of Biomechanics, 18(5): 307-316.

135. Grimby, L. & Hannerz, J. (1974). Differences in recruitment order anddischarge pattern of motor units in the early and late flexin reflexcomponents in man. Acta Physiologica Scandinavica, 90: 555-564.

136. Grimby, L. & Hannerz, J. (1977). Firing rate and recruitment order oftoe extensor motor units in different modes of voluntary contraction.Journal of Physiology, 264: 865-875.

137. Grimby, L. & Hannerz. J. (1968). Recruitment of motor units onvoluntary contraction: Changes induced by proprioceptive afferent activity.Journal of Neurology, 31: 565-573.

138. Guezennec, C.Y., Gilson, E. & Serrurier, B. (1990). Comparativeeffects of hindlimb suspension and exercise on skeletal muscle myosinisozymes in rats. European Journal of Applied Physiology andOccupational Physiology, 60(6): 430-436.

139. Gunning, P. & Hardeman, E. (1991). Multiple mechanisms regulatemuscle fiber diversity. FASEB Journal, 5(15): 3064-3070.

140. Häkkinen, K. & Komi, P.V. (1983). Electromyographic changes duringstrength training and detraining. Medicine and Science in Sports andExercise, 15(6): 455-460.

141. Häkkinen, K. & Komi, P.V. (1985a). Effect of explosive type strengthtraining on electromyographic and force production characteristics of leg

221

extensor muscles during concentric and various stretch-shorteningcycle exercises. Scandinavian Journal of Sports Sciences, 7(2): 65-76.

142. Häkkinen, K. & Komi, P.V. (1986). Training induced changes inneuromuscular performance under voluntary and reflex conditions.European Journal of Applied Physiology, 55: 147-155.

143. Häkkinen, K., Alén, M. & Komi, P.V. (1985). Changes in isometricforce- and relaxation-time, electromyographic and muscle fibrecharacteristics of human skeletal muscle during strength training anddetraining. Acta Physiologica Scandinavica, 125: 573-585.

144. Häkkinen, K., Kallinen, M., Komi, P.V. & Kauhanen, H. (1991).Neuromuscular adaptations during short-term "normal" and reducedtraining periods in strength athletes. Electromyography and clinicalneurophysiology, 31: 35-42.

145. Häkkinen, K., Kallinen, M., Linnamo, V. Pastinen, U-M., Newton, R.U.& Kraemer, W.J. (1996). Neuromuscular adaptations during bilateralversus unilateral strength training in middle-aged and elderly men andwomen. Acta Physiologica Scandinavica, 158: 77-88.

146. Häkkinen, K., Komi, P.V. & Tesch, P.A. (1981). Effect of combinedconcentric and eccentric strength training and detraining on force-time,muscle fibre, and metabolic characteristics of leg extensor muscle.Scandinavian Journal of Sports Sciences, 3: 50-58.

147. Häkkinen, K., Komi, P.V., Alén, M. & Kauhanen, H. (1987). EMG,muscle fibre and force production characteristics during a 1 year trainingperiod in elite weight lifters. European Journal of Applied Physiology, 56:419-427.

148. Häkkinen, K., Komi, P.V. & Alén, M. (1985b). Effect of explosive typestrength training on isometric force- and relaxation-time,electromyographic and muscle fibre characteristics of leg extensormuscles. Acta Physiologica Scandinavica, 125(4): 587-600.

149. Häkkinen, K., Pastinen, U.M., Karsikas, R. & Linnamo, V. (1995).Neuromuscular performance in voluntary bilateral and unilateralcontraction and during electrical stimulation in men at different ages.European Journal of Applied Physiology & Occupational Physiology, 70(6):518-527.

222

150. Harridge, S.D.R., Bottinelli, R., Canepari, M., Pellegrino, M.A.,Reggiani, C., Esbjörnsson, M. & Saltin, B. (1996). Whole-muscle andsingle-fibre contractile properties and myosin heavy chain isoforms inhumans. European Journal of Physiology, 432(5): 913-920.

151. Harridge, S.D.R., Bottinelli, R., Canepari, M., Pellegrino, M, Reggiani,C., Esbjörnsson, M., Balsom, P.D. & Saltin, B. (1998). Sprint training, invitro and in vivo muscle function, and myosin heavy chain expression.Journal of Applied Physiology, 84(2): 442-449.

152. Harridge, S.D.R., Kryger, A. & Stensgaard, A. (1999). Knee extensorstrength, activation, and size in very elderly people following strengthtraining. Muscle and Nerve, 22: 831-839.

153. Hellsten, Y., Apple, F.S. & Sjodin, B. (1996). Effect of sprint cycletraining on activities of antioxidant enzymes in human skeletal muscle.Journal of Applied Physiology, 81(4): 1484-1487.

154. Henneman, E. Somjen, G. & Carpenter, D.O. (1964). Functionalsignificance of cell size in spinal motoneurons. Journal ofNeurophysiology, 28: 560-580.

155. Hennessey, L.C. & Watson, A.W.S. (1994). The interference effects oftraining for strength and endurance simultaneously. Journal of Strengthand Conditioning Research, 8(1): 12-19.

156. Henriksson, J. & Reitman, J.S. (1976). Quantitative measures ofenzyme activities in type I and type II muscle fibres of man after training.Acta Physiologica Scandinavica, 97(3): 392-397

157. Henriksson-Larsén, K., Wretling, M-L., Lorentzon, R. & Öberg, L.(1992). Do muscle fibre size and fibre angulation correlate in pennatedhuman muscles? European Journal of Applied Physiology, 64: 68-72.

158. Herbert, R.D. & Belnave, R.J. (1993). The effect of position ofimmobilisation on resting length, resting stiffness, and weight of the soleusmuscle of the rabbit. Journal of Orthopaedic Research, 11: 358-366.

159. Herbert, R.D. & Gandevia, S.C. (1996). Muscle activation in unilateraland bilateral efforts assessed by motor nerve and cortical stimulation.Journal of Applied Physiology, 80(4): 1351-1356.

223

160. Herbert, R.D., Dean, C. & Gandevia, S.C. (1998). Effects of real andimagined training on voluntary muscle activation during maximal isometriccontractions. Acta Physiologica Scandinavica, 163: 361-368.

161. Herring, S.W., Grimm, A.F. & Grimm, B.R. (1984). Regulation ofsarcomere number in skeletal muscle: a comparison of hypotheses.Muscle & Nerve, 7: 161-173.

162. Heslinga, J.W., te Kronnie, G. & Huijing, P.A. (1995). Growth andimmobilization effects on sarcomeres: a comparison betweengastrocnemius and soleus muscles of the adult rat. European Journal ofApplied Physiology, 70: 49-57.

163. Hickson, R.C., Heusner, W.W. & Van Huss, W.D. (1976). Skeletalmuscle enzyme alterations after sprint and endurance training. Journal ofApplied Physiology, 40: 868-872.

164. Higbie, E.J., Cureton, K.J., Warren, G.L. & Prior, B. (1996). Effects ofconcentric and eccentric training on muscle strength, cross-sectional area,and neural activation. Journal of Applied Physiology, 81(5): 2173-2181.

165. Hoeger, W.W.K., Hopkins, D.R., Barette, S.L. & Hale, D.F. (1990).Relationship between repetitions and selected percentages of onerepetition maximum: a comparison between untrained and trained malesand females. Journal of Applied Sport Science Research, 4(2): 47-54.

166. Hoff, J. & Almasbakk, B. (1995). The effects of maximum strengthtraining on throwing velocity and muscle strength in female team-handballplayers. Journal of strength and conditioning research 9(4): 255-258.

167. Hopkins, W.G. (2000). Sportscience: A new view of statistics.http://www.sportsci.org/resource/stats/index.html.

168. Horber, F.F., Scheidegger, J.T., Grunig, B.E. & Frey, F.J. (1985). Thighmuscle mass and function in patients treated with glucocorticoids.European Journal of Clinical Investigation, 15(6): 302-307.

169. Hortobágyi, T. & Katch, F. (1990). Role of concentric force in limitingimprovement in muscular strength. Journal of Applied Physiology, 6(2):650-658.

224

170. Hortobágyi, T., Katch, F.I. & LaChance, P.F. (1989). Interrelationsamong various measures of upper body strength assessed by differentcontraction modes. Evidence for a general strength development.European Journal of Applied Physiology, 58: 749-755.

171. Hortobágyi, T., Barrier, J., Beard, D., Braspennincx, J., Koens, P.,Devita, P., Dempsey, L. & Lambert, J. (1996). Greater initial adaptations tosubmaximal muscle lengthening than maximal shortening. Journal ofApplied Physiology, 81(4): 1677-1682.

172. Hortobágyi, T., Dempsey, L., Fraser, D., Zheng, D., Hamilton, G.,Lambert, J. & Dohm, L. (2000). Changes in muscle strength, muscle fibresize and myofibrillar gene expression after immobilization and retraining inhumans. Journal of Physiology, 524(1): 293-304.

173. Housh, D.J. & Housh, T.J. (1993). The effects of unilateral velocity-specific concentric strength training. Journal of Orthopaedic and SportsPhysical Therapy, 17(5): 252-256.

174. Housh, D.J., Housh, T.J., Johnson, G.O. & Chu, W. (1992).Hypertrophic response to unilateral concentric isokinetic resistancetraining. Journal of Applied Physiology, 73(1): 65-70.

175. Howard, J.D. & Enoka, R.M. (1991). Maximum bilateral contractionsare modified by neurally mediated interlimb effects. Journal of AppliedPhysiology, 70(1): 306-316.

176. Huijing, P.A. (1999). Muscle as a collagen fibre reinforced composite: areview of force transmission in muscle and whole limb. Journal ofBiomechanics, 32: 329-345.

177. Hunter, S.K., Thompson, M.W., Ruell, P.A., Harmer, A.R., Thom, J.M.,Gwinn, T.H. & Adams, R.D. (1999). Human skeletal sarcoplasmicreticulum Ca2+ uptake and muscle function with aging and strengthtraining. Journal of Applied Physiology, 86: 1858-1865.

178. Irving, M., Piazzesi, G., Lucii, L., Sun, Y.B., Harford, J.J., Dobbie, I.M.,Ferenczi, M.A., Reconditi, M. & Lombardi, V. (2000). Conformation of themyosin motor during force generation in skeletal muscle. Nature StructuralBiology, 7(6): 482-485.

179. Jacobs, I., Esbjörnsson, M., Sylven, C., Holm, I. & Jansson, E. (1987).

225

Sprint training effects on muscle myoglobin, enzymes, fiber types, andblood lactate. Medicine and Science in Sports and Exercise, 19: 368-374.

180. Jacobs, R., Bobbert, M.F. & Ingen Schenau, G.J. van (1993). Functionof mono- and biarticular muscles in running. Medicine and Science inSports and Exercise, 25(10): 1163-1173.

181. Jacobs, R. & Ingen Schenau, G.J van. (1992). Intermuscularcoordination during a sprint push-off. Journal of Biomechanics, 25(9):953-965.

182. Jakobi, J.M. & Cafarelli, E. (1998). Neuromuscular drive and forceproduction are not altered during bilateral contractions. Journal of AppliedPhysiology, 84(1): 200-206.

183. Jansson, E., Esbjörnsson, H.I. & Jacobs, I. (1990). Increase in theproportion of fast twitch muscle fibres by sprint training in males. ActaPhysiologica Scandinavica, 140: 359-363.

184. Jenkins, W.L, Thackaberry, M. & Killian, C. (1984). Speed specificisokinetic training. Journal of Orthopaedic and Sports Physical Therapy,6(3): 181-183.

185. Johnson, B.L. (1972). Eccentric versus concentric muscle training forstrength development. Medicine and Science in Sports, 4: 111-115.

186. Johnson, B.L., Adamczyk, J.W., Tenoe, K.O. & Stromme, S.B. (1976).Comparison of concentric and eccentric muscle training. Medicine andScience in Sports, 8(1): 35-38.

187. Jones, D.A. (1992). Strength of skeletal muscle and the effects oftraining. British Medical Bulletin, 48(3): 592-604.

188. Jones, D.A. & Rutherford, O.M. (1987). Human muscle strengthtraining: The effects of three different regimes and the nature of theresultant changes. Journal of Physiology, 74: 233-256.

189. Jones, D.A., Rutherford, O.M. & Parker, D.F. (1989). Physiologicalchanges in skeletal muscle as a result of strength training. QuarterlyJournal of Experimental Physiology, 74(3): 233-256.

226

190. Jostarndt-Fogen, K., Puntschart, A., Hoppeler, H. & Billeter, R.(1998). Fibre-type specific expression of fast and slow essential myosinlight chain mRNAs in trained skeletal muscles. Acta PhysiologicaScandinavica, 164(3): 299-308.

191. Jürimäe, J. (1997). Skeletal muscle myosin heavy chain isoformexpression and resistance activity: a review. Acta KinesiologiaeUniversitatis Tartuensis, 2: 7-25.

192. Jürimäe, J., Abernethy, P.J., Blake, K. & McEnierty, M.T. (1996).Changes in the myosin heavy chain isoform profile of the triceps brachiimuscle following 12 weeks of resistance training. European Journal ofApplied Physiology and Occupational Physiology, 74(3): 287-292.

193. Kalmar, J.M. & Cafarelli, E. (1999). Effects of caffeine onneuromuscular function. Journal of Applied Physiology, 87(2): 801-808.

194. Kanehisa, H. & Miyashita, M. (1983). Specificity of velocity in strengthtraining. European Journal of Applied Physiology, 52: 104-106.

195. Kannus, P., Jaruinen, M. & Lehto, M. (1991). Maximal peak torque as apredictor of angle-specific torques of hamstring and quadriceps muscles inman. European Journal of Applied Physiology, 63: 112-118.

196. Karst, G. & Hasan, Z. (1987). Antagonist muscle activity during forearmmovements under varying kinematic and loading conditions. ExperimentalBrain Research, 67: 391-401.

197. Kato, M., Murakami, S. & Yasuda, K. (1985). Behavior of single motorunits of human tibialis anterior muscle during voluntary shorteningcontraction under constant load torque. Experimental Neurology, 90: 238-253.

198. Kaufman, K.R., An, K-M. & Chao, Y.S. (1989). Incorporation of musclearchitecture into the muscle length-tension relationship. Journal ofBiomechanics, 22(8/9): 943-948.

199. Kawahats, K. (!983). Switching mechanism of neuromuscular activity intop world athletes. In: Matsui, H. and Kobayashi, K. (eds.), BiomechanicsVIII-A & B: Proceedings of the Eighth International Congress ofBiomechanics, Nagoya, Japan, Champaign, Ill., Human Kinetics

227

Publishers, pp. 289-293.

200. Kawakami, Y., Abe, T. & Fukunaga, T. (1993). Muscle-fiber pennationangles are greater in hypertrophied than in normal muscles. Journal ofApplied Physiology, 74(6): 2740-2744.

201. Kawakami, Y., Abe, T., Kuno, S-Y. & Fukunaga, T. (1995). Training-induced changes in muscle architecture and specific tension. EuropeanJournal of Applied Physiology, 72: 37-43.

202. Kawakami, Y., Ichinose, Y. & Fukunaga, T. (1998). Architectural andfunctional features of human triceps surae muscles during contraction.Journal of Applied Physiology, 85(2): 398-404.

203. Kawakami, Y., Ichinose, Y., Kubo, K., Ito, M., Imai, M. & Fukunaga, T.(2000). Architecture of contracting human muscles and its functionalsignificance. Journal of Applied Biomechanics, 16: 88-98.

204. Kirkwood, P.A. & Sears, T.A. (1991). Cross-correlation analyses ofmotoneurone inputs in a coordinated motor act. In: Kruger, J., Springer-Verlag Series in Synergetics: Neuronal Cooperativity. Springer, Berlin, pp.225-248.

205. Kitai, T.A. & Sale, D.G. (1989). Specificity of joint angle in isometrictraining. European Journal of Applied Physiology and OccupationalPhysiology, 58: 744-748.

206. Koh, T.J. (1995). Do adaptations in serial sarcomere number occurwith strength training. Human Movement Science, 14: 61-77.

207. Koh, T.J., Grabiner, M.D. & Clough, C.A. (1993). Bilateral deficit islarger for step than for ramp isometric contractions Journal of AppliedPhysiology, 74(3): 1200-1205.

208. Komi, P.V. & Buskirk, E.R. (1972). Effect of eccentric and concentricmuscle conditioning on tension and electrical activity in human muscleErgonomics, 15: 417-434.

209. Komi, P.V. (1984). Physiological and mechanical correlates of musclefunction: Effects of muscle structure and stretch-shorten cycle on forceand speed. In Terjung, R.L. (ed). Exercise and Sports Science Reviews.

228

Lexington: The Collamore Press, 81-121.

210. Kromodihardjo, S. & Mital, A. (1987). Biomechanical analysis ofmanual lifting tasks. Journal of Biomedical Engineering, 109: 132-138.

211. Kumagai, K., Abe, T., Brechue, W.F., Ryushi, T., Takano, S. & Mizuno,M. (2000). Sprint performance is related to muscle fascicle length in male100-m sprinters. Journal of Applied Physiology, 88(3): 811-816.

212. Kuno, S., Katsuta, S., Akisada, M., Anno, I. & Matsumoto, K. (1990).Effect of strength training on the relationship between magnetic resonancerelaxation time and muscle fibre composition. European Journal of AppliedPhysiology and Occupational Physiology, 61(1-2): 33-36.

213. Lacerte, M., deLateur, B.J., Alquist, A.D. & Questad, K.A. (1992).Concentric versus combined concentric-eccentric isokinetic trainingprograms: effect on peak toque of human quadriceps femoris muscle.Archives of Physical Medicine and Rehabilitation, 73(11): 1059-1062.

214. Larsson, L. & Moss, R.L. (1993). Maximum velocity of shortening inrelation to myosin isoform composition in single fibres from human skeletalmuscles. Journal of Physiology, 472: 595-614.

215. Laughman, R.K., Youdas, J.M., Garrett, T.R. & Chao, E.Y.S. (1983).Strength changes in the normal quadriceps femoris muscle as a result ofelectrical stimulation. Physical Therapy, 63(4): 494-499.

216. Leong, B., Kamen, G., Patten, C. & Du, C.C. (1995). Motor unitdischarge rates in older weight lifters during maximal voluntarycontractions. Medicine and Science in Sports and Exercise, 27(5): S33.

217. Lesmes, G. (1978). Muscle strength and power changes duringmaximal isokinetic training. Medicine and Science in Sports and Exercise,10: 266-269.

218. Lestienne, F. (1979). Effects of inertial load and velocity on the brakingprocess of voluntary limb movements. Experimental Brain Research, 35:407-418.

219. Lieber, R.L. & Blevins, F.T. (1989). Skeletal muscle architecture of therabbit hindlimb: functional implications of muscle design. Journal of

229

Morphology, 199: 93-101.

220. Lind, A.R. & Petrofsky, J.S. (1978). Isometric tension from rotarystimulation of fast and slow cat muscles, Muscle & Nerve, 1(3): 213-218.

221. Lindh, M. (1979). Increase of muscle strength from isometricquadriceps exercises at different knee angles. Scandinavian Journal ofRehabilitative Medicine, 11: 33-36.

222. Linossier, M.T., Dormois, D., Geyssant, A. & Denis, C. (1997).Performance and fibre characteristics of human skeletal muscle duringshort sprint training and detraining on a cycle ergometer. EuropeanJournal of Applied Physiology and Occupational Physiology, 75(6): 491-498.

223. Lloyd, A.R., Gandevia, S.C. & Hales, J.P. (1991). Muscle performance,voluntary activation, twitch properties and perceived effort in normalsubjects and patients with the chronic fatigue syndrome. Brain, 114(Pt 1A):85-98.

224. Loeb, G.E., Pratt, C.A., Chanaud, C.M. & Richmond, F.J.R. (1987).Distribution and innervation of short, interdigitated muscle fibers in parallel-fibered muscles of the cat hindlimb. Journal of Morphology, 191: 1-15.

225. Lowey, S., Waller, G.S. & Trybus, K.M. (1993). Skeletal muscle myosinlight chains are essential for physiological speeds of shortening. Nature,365(6445): 454-456.

226. Lyle, N. & Rutherford, O.M. (1998). A comparison of voluntary versusstimulated strength training of the human adductor pollicis muscle. Journalof Sports Sciences, 16(3): 267-270.

227. Lynn, P.A., Bettles, N.D., Hughes, A.D. & Johnson, S.W. (1978).Influence of electrode geometry on bipolar recordings of the surfaceelectromyogram. Medical and Biological Engineering and Computing, 16:651-660.

228. Lynn, R. & Morgan, D.L. (1994). Decline running produced moresarcomeres in rat vastus intermedius muscle fibers than does inclinerunning. Journal of Applied Physiology, 77(3): 1439-1444.

230

229. MacDougall, J.D., Ward, G.R., Sale, D.G. & Sutton, J.R. (1977).Biochemical adaptation of human skeletal muscle to heavy resistancetraining and immobilization. Journal of Applied Physiology, 43: 700.

230. MacDougall, J.D., Gibala, M.J., Tarnopolsky, M.A., MacDonald, J.R.,Interisano, S.A. & Yarasheski, K.E. (1995). The time course for elevatedmuscle protein synthesis following heavy resistance exercise. CanadianJournal of Applied Physiology, 20(4): 480-486.

231. MacDougall, J.D., Hicks, A.L., MacDonald, J.R., McKelvie, R.S.,Green, H.J. & Smith, K.M. (1998). Muscle performance and enzymaticadaptations to sprint interval training. Journal of Applied Physiology, 84(6):2138-2142.

232. MacDougall, J.D., Sale, D.G., Alway, S.E. & Sutton, J.R. (1984).Muscle fibre number in biceps brachii in bodybuilders and control subjects.Journal of Applied Physiology, 57:1399-1403.

233. MacDougall, J.D., Tarnopolsky, M.A., Chesley, A. & Atkinson, S.A.(1992). Changes in muscle protein synthesis following heavy resistanceexercise in humans: A pilot study. Acta Physiologica Scandinavica, 146:403-404.

234. MacDougall, J.D., Ward, G.R., Sale, D.G. & Sutton, J.R. (1977).Biochemical adaptation of human skeletal muscle to heavy resistancetraining and immobilization. Journal of Applied Physiology 43(4): 700-703.

235. Mann, R. & Herman, J. (1985). Kinematic analysis of Olympic sprintperformance: men’s 200 meters. International Journal of SportBiomechanics, 1: 151-162.

236. Mannion, A.F., Jakeman, P.M. & Willan, L.T. (1995). Skeletal musclebuffer value, fibre type distribution and high intensity exercise performancein man. Experimental Physiology, 80: 89-101.

237. Mao, J.J., Major, P.W. & Osborn, J.W. (1996). Coupling electrical andmechanical outputs of human jaw muscles undertaking multidirectionalbite-force tasks. Archives of Oral Biology, 41(12):1141-1147.

238. Marsden, C.D., Obeso, J.A. & Rothwell, J.C. (1983). The function ofthe antagonist muscle during fast limb movements in man. Journal of

231

Physiology, 335: 1-13.

239. Martin, L, Cometti, G., Pousson, M. & Morlon, B. (1994). The influenceof electrostimulation on mechanical and morphological characteristics ofthe triceps surae. Journal of Sports Sciences, 12: 377-381.

240. Matano, T., Tamai, K. & Kurokawa, T. (1994). Adaptation of skeletalmuscle in limb lengthening: A light diffraction study on the sarcomerelength In Situ. Journal of Orthopaedic Research, 12: 193-196.

241. McCaw, S.T., & Melrose,D.R. (1999). Stance width and bar load effectson leg muscle activity during the parallel squat. Medicine and Science inSports and Exercise, 31(3): 428-436.

242. McDonnagh, M.J & Davies, C.T.M. (1984). Adaptative response tomammalian skeletal muscle to exercise with high load. European Journalof Applied Physiology, 52:139.

243. McLaughlin, T.M., Dillman, C.J. & Lardner, T.J. (1977). A kinematicmodel of performance in the parallel squat by champion powerlifters.Medicine and Science in Sports, 9(2): 128-133.

244. Mero, A. & Komi, P.V. (1987). Electromyographic activity in sprinting atspeeds ranging from sub-maximal to supra-maximal. Medicine andScience in Sports and Exercise, 19(3): 266-274.

245. Mero, A. & Komi, P.V. (1990). Reaction time and electromyographicactivity during a sprint start. European Journal of Applied Physiology, 61:73-80.

246. Mero, A., Luhtanen, P. & Komi, P.V. (1983). A biomechanical study ofthe sprint start. Scandinavian Journal of Sports Science, 5(1): 20-28.

247. Merton, P.A. (1954). Voluntary strength and muscle fatigue. Journal ofPhysiology, 123: 553-564.

248. Meyers, C.R. (1967). Effects of two isometric routines on strength sizeand endurance in exercised and nonexercised arms. Research Quarterly,38: 430-440.

249. Miffed, R. (1988). Strength and flexibility considerations for exercise

232

prescription. In Blair, S.N., Painter, P., Russie, R., Smith, L. & Taylor, C.(eds). Resource Manual for Guidelines for Exercise Testing andPrescription. Philadelphia, Lea & Febiinger, 263-270.

250. Miller, R.G., Mirka, A. & Maxfield, M. (1981). Rate of tensiondevelopment in isometric contractions of a human hand muscle.Experimental Neurology, 73: 267-285.

251. Milner-Brown, H., Stein, R.B. & Yemm, R. (1973). The orderlyrecruitment of motor units during voluntary isometric contractions. Journalof Physiology, 230: 359-370.

252. Moffroid, M. & Whipple, R.H. (1970). Specificity of speed of exercise.Physical Therapy, 50: 1692-1700.

253. Monti, R.J., Roy, R.R., Hodgson, J.A. & Edgerton, V.R. (1999).Transmission of forces with mammalian skeletal muscles. Journal ofBiomechanics, 32: 371-380.

254. Morgan, D.L. (1990). New insights into the behaviour of muscle duringactive lengthening. Biophysical Journal, 57: 209-221.

255. Moritani, T. (1993). Neuromuscular adaptations during the acquisitionof muscle strength, power and motor tasks. Journal of Biomechanics. 26(Suppl 1): 95-107.

256. Moritani, T., Oddson, L. & Thorstensson, A. (1990). Electromyographicevidence of selective fatigue during the eccentric phase ofstretch/shortening cycles in man. European Journal of Applied Physiology& Occupational Physiology, 60(6): 425-429.

257. Moritani, T. & DeVries, H.A. (1979). Neural factors versus hypertrophyin the time course of muscle strength gain. American Journal of PhysicalMedicine, 58(3): 115-130.

258. Moritani, T. & Shibata, M. (1994). Premovement electromyographicsilent period and á-motoneuron excitability. Journal of Electromyographyand Kinesiology, 4(1): 27-36.

259. Moritani, T. (1992). Time course of adaptations during strength andpower training. In, Komi, P.V. (ed.), Strength and power in sport, Oxford,

233

Blackwell Scientific Publications, pp. 266-278.

260. Moritani, T., Muro, M., Ishida, K. & Tanaguchi, S. (1987).Electromyographic analysis of the effects of muscle power training.Journal of Medicine and Sports Sciences (Japan), 1: 23-32.

261. Morrissey, M.C., Harman, E.A. & Johnson, M.J. (1995). Resistancetraining modes: specificity and effectiveness. Medicine and Science inSports and Exercise, 27(5): 648-660.

262. Muhl, Z.F. (1982). Active length-tension relation and the effect ofmuscle pinnation of fiber lengthening. Journal of Morphology, 173:285-292.

263. Murphy, A.J. & Wilson, G.J. (1995). A comparison of isoinertial andisokinetic tests of muscular function. In: Hakkinen, K. (ed.) XVth Congressof the International Society of Biomechanics, July 2-6, 1995, Jyvaskyla:Book of Abstracts, Jyvaskyla, University of Jyvaskyla.

264. Murphy, A.J., Wilson, G.J., Pryor, J.F. & Newton, R.U. (1995).Isometric assessment of muscular function: the effect of joint angle.Journal of Applied Biomechanics, 11(2): 205-215.

265. Nakazawa, K., Kawakami, Y., Fukunaga, T., Yano, J. & Miyashita, M.(1993). Differences in activation patterns in elbow flexor muscles duringisometric, concentric and eccentric contractions. European Journal ofApplied Physiology, 66: 214-220.

266. Nakazawa, K., Masani, K., Miyashita, M. & Yano, H. (1994). EMGactivities of mono- and bi-articular muscles during goal-directed ballisticmovement. Journal of Human Movement Studies, 13: 601-610.

267. Nardone, A., Romano, C. & Schieppati, E. (1989). Selectiverecruitment of high threshold motor units during voluntary isotoniclengthening of active muscles. Journal of Physiology, 409: 451-471.

268. Nardone, A. & Schieppati, M. (1988). Shift of activity from slow to fastmuscle during voluntary lengthening contractions of the triceps suraemuscles in humans. Journal of Physiology, 395: 363-381.

269. Narici, M.V., Hoppeler, H., Kayser, B., Landoni, L., Claassen, H.,

234

Gavardi, C., Conti, M. & Cerretelli, P. (1996). Human quadriceps cross-sectional area, torque and neural activation during 6 months strengthtraining. Acta Physiologica Scandinavica, 157: 175-186.

270. Narici, M.V. & Kayser, B. (1995). Hypertrophic response of humanskeletal muscle to strength training in hypoxia and normoxia. EuropeanJournal of Applied Physiology, 70: 213-219.

271. Narici, M.V., Roi, G.S., Landoni, L., Minetti, A.E. & Cerretelli, P. (1989).Changes in force, cross-sectional area and neural activation duringstrength training and detraining of the human quadriceps. EuropeanJournal of Applied Physiology, 59: 310-319.

272. Nemeth, G. & Ohlsen, H. (1987). Moment arm lengths of the erectorspinae and rectus abdominis muscles obtained in vivo with computedtomography. In: Jonsson, B. (ed.), Biomechanics X-A, Human KineticsPublishers, Champaign, Ill., pp.189-193.

273. Newton, R.U., Murphy, A.J., Humphries, B.J., Wilson, G.J., Kraemer,W.J. & Hakkinen, K. (1997). Influence of load and stretch shortening cycleon the kinematics, kinetics and muscle activation that occurs duringexplosive upper-body movements. European Journal of AppliedPhysiology and Occupational Physiology, 75(4): 333-342.

274. Nikituk, B. & Samoilov, N. (1990). The adaptive mechanisms of musclefibres to exercise and possibilities for controlling them. Teoriya i PraktikaFizischelskoi Kultury, 5: 11-14.

275. Ninos, J.C., Irrgang, J.J., Burdett, R. & Weiss, J.R. (1997).Electromyographic analysis of the squat performed in self-selected lowerextremity neutral rotation and 30 degrees of lower extremity turn-out fromthe self-selected neutral position. The Journal of Orthopaedic and SportsPhysical Therapy, 25(5): 307-315.

276. Norman, R.W. & Komi, P. (1979). Electromechanical delay in skeletalmuscle under normal movement conditions. Acta PhysiologicaScandinavica, 106: 241-248.

277. O’Brien, G.A., Corbett, J.M., Dunn, M.J., cumming, D.V., May, A.J. &Yacoub, M.H. (1992). Electrophoretic analysis of electrically trainedskeletal muscle. Electrophoresis, 13(9-10): 726-728.

235

278. O’Bryant, H., Byrd, R. & Stone, M. (1988). Cycle ergometerperformance and maximum leg and hip strength adaptations to twodifferent methods of weight-training. Journal of Applied Sport ScienceResearch, 2(2): 27-30.

279. Oda, S. & Moritani, T. (1994). Maximal isometric force and neuralactivity during bilateral and unilateral elbow flexion in humans. EuropeanJournal of Applied Physiology, 69: 240-243.

280. Oddsson, L. & Thorstensson, A. (1990). Task specificity in the controlof intrinsic trunk muscles in man. Acta Physiologica Scandinavica, 139:123-131.

281. Ohira, Y., Yoshinaga, T., Yasui, W., Ohara, M. & Tanaka, T. (2000).Effects of hindlimb suspension with stretched or shortened muscle lengthon contractile properties of rat soleus. Journal of Applied Biomechanics,16: 80-87.

282. Ohtsuki, T. (1983). Decrease in human voluntary isometric armstrength induced by simultaneous bilateral exertion. Behavioural BrainResearch, 7: 165-178.

283. Okada, M. (1987). Effect of muscle length on surface EMG wave formsin isometric contractions. European Journal of Applied Physiology, 56:482-486.

284. Ortenblad, N., Sjogaard, G. & Madsen, K. (2000). Impairedsarcoplasmic reticulum Ca2+ release rate after fatiguing stimulation in ratskeletal muscle. Journal of Applied Physiology, 89: 210-217.

285. Ostrowski, K.J., Wilson, G.J., Weatherby, R.P. & Murphy, P.W. (1997).The effect of weight training volume on hormonal output and muscular sizeand function. Journal of Strength and Conditioning Research, 11(1):148-154.

286. Ozmun, J.C., Mikesky, A.E. & Surberg, P.R. (1994). Neuromuscularadaptations following prepubescent strength training. Medicine andScience in Sports and Exercise, 26(4): 510-514.

287. Palmieri, G.A. (1987). Weight training and repetition speed. Journal ofApplied Sport Science Research, 1: 36-38.

236

288. Pandy, M.G. & Zajac, F.E. (1991). Optimal muscular coordinationstrategies for jumping. Journal of Biomechanics, 24(1): 1-10.

289. Patten, C., Kamen, A., Rowland, D. & Du, C.C. (1995). Rapidadaptations of motor unit firing rate during the initial phase of strengthdevelopment. Medicine and Science in Sports and Exercise, 27(5): S33.

290. Perneger, T.V. (1998). What’s wrong with Bonferroni adjustments.British Medical Journal, 316: 1236-1238.

291. Perrine, J. & Edgerton, V. (1978). Muscle force-velocity and power-velocity relationships under isokinetic loading. Medicine and Science inSports, 10(3): 159-166.

292. Person, R. (1974). Rhythmic activity of a group of human motoneuronsduring voluntary contraction of a muscle. Electroencephalography andClinical Neurophysiology, 36: 585-595.

293. Person, R.S. & Kudina, L. (1970). Discharge frequency and dischargepattern of motor units during voluntary and reflex activation. BrainResearch, 602: 104-110.

294. Petersen, S. (1988). Functional adaptations to velocity-specificresistance training. PhD Dissertation, University of Alberta, 1988.

295. Petersen, S.R., Bagnall, K.M., Wenger, H.A., Reid, D.C., Castor, W.R.& Quinney, H.A. (1989). The influence of velocity-specific resistancetraining on the in vivo torque-velocity relationship and the cross-sectionalarea of quadriceps. Journal of Orthopaedic and Sports Physical Therapy,10(11): 456-462.

296. Petersen, S.R., Bell, G.J., Bagnall, K.M. & Quinney, H.A. (1991). Theeffects of concentric resistance training on eccentric peak torque andmuscle cross-sectional area. Journal of Orthopaedic and Sports PhysicalTherapy, 13(3): 132-137.

297. Pette, D. & Vrbovà, G. (1992). Adaptation of mammalian skeletalmuscle fibers to chronic electrical stimulation. Reviews of PhysiologyBiochemistry & Pharmacology, 120:115-202.

298. Poliquin, C. (1992). Applied strength training: Part 1 Short term

237

periodisation. Sports Coach, 15(3): 25-28.

299. Pousson, M., Amaridis, I.G., Cometti, G. & Van Hoecke, J. (1999).Velocity-specific training in elbow flexors. European Journal of AppliedPhysiology, 80(4): 367-372.

300. Pratt, C.A., Chanaud, C.M. & Loeb, G.E. (1991). Functionally complexmuscles of the cat hindlimb. IV. Intramuscular distribution of movementcommand signals and cutaneous reflexes in broad, bifunctional thighmuscles. Experimental Brain Research, 85: 281-299.

301. Raasch, P.J. & Morehouse, L.E. (1957). Effect of static and dynamicexercises on muscular strength and hypertrophy. Journal of AppliedPhysiology, 11(1): 29-34.

302. Rack, P.M. & Westbury, D.R. (1969). The effects of length and stimulusrate on tension in the isometric cat soleus muscle. Journal of Physiology,204(2): 443-60.

303. Rahmani, A., Dalleau, G., Viale, F., Hautier, C. & Lacour, J-R. (2000).Validity and reliability of a kinematic device for measuring the forcedeveloped during squatting. Journal of Applied Biomechanics, 16: 26-35.

304. Rich, C. & Cafarelli, E. (2000). Submaximal motor unit firing rates after8 wk of isometric resistance training. Medicine and Science in Sport andExercise, 32(1): 190-196.

305. Roberts, A.D., Billeter, R. & Howald, H. (1982). Anaerobic muscleenzyme changes after interval training. International Journal of SportsMedicine, 3: 18-21.

306. Robertson, D.G.E. & Fleming, D. (1987). Kinetics of standing broadand vertical jumping. Canadian Journal of Sports Science, 12(1): 19-23.

307. Romanguére, P., Vedel, J. & Pagni, S. (1992). Effects of tonic vibrationreflex on motor unit recruitment in human wrist extensor muscles. BrainResearch, 602: 32-40.

308. Roy, R.R. & Edgerton, V.R. (1991). Skeletal muscle architecture andperformance. In Komi, P.V. (Ed.). Strength and Power in Sport, City:

238

Blackwell Scientific Publications, pp. 115-129.

309. Rube, N. & Secher, N.H. (1990). Effect of training on central factors infatigue following two- and on-leg static exercise in man. Acta PhysiologicaScandinavica, 141: 87-95.

310. Rutherford, O.M. & Jones, D.A. (1986). The role of learning andcoordination in strength training. European Journal of Applied Physiologyand Occupational Physiology, 55(1): 100-105.

311. Rutherford, O.M. & Jones, D.A. (1992). Measurement of fibrepennation using ultrasound in the human quadriceps in vivo. EuropeanJournal of Applied Physiology, 65:433-437.

312. Rutherford, O.M., Greig, C.A., Sargeant, A.J. & Jones, D.A. (1986).Strength training and power output: transference effects in the humanquadriceps muscle. Journal of Sports Science, 4: 101-107.

313. Sacks, R.D. & Roy, R.R. (1982). Architecture of the hind limb of muscleof cats: functional significance. Journal of Morphology, 173: 185-195.

314. Sale, D.G. (1987). Influence of exercise and training on motor uniactivation. In Pandolf (Ed.). Exercise and Sport Science Reviews.MacMillan Publishing Co. Inc, New York, 15: 95-151.

315. Sale, D.G. (1988). Neural adaptation to resistance exercise. Medicineand Science in Sports and Exercise, 20: S135-S145.

316. Sale, D.G., Marin, J.E. & Moroz, D.E. (1992). Hypertrophy withoutincreased isometric strength after weight training. European Journal ofApplied Physiology, 64: 51-55.

317. Sale, D.G. (1991). Testing strength and power. In: MacDougall J.D.,H.A. Wenger and H.J. Green, eds. Physiological testing of the high-performance athlete. Champaign, IL: Human Kinetics, pp. 21-103.

318. Saltin, B. & Gollnick, P.D. (1983). Skeletal muscle adaptability:Significance for metabolism and performance. In: Peachey, L.D. (ed.).Handbook of Physiology, section 10: Skeletal muscle, Bethesda, Md.,American Physiological Society, pp. 555-631.

239

319. Schantz, P.G., Moritani, T., Kraals, E., Johnson, E. & Lundh, A.(1989). Maximal voluntary force of bilateral and unilateral leg extension.Acta Physiologica Scandinavica, 136: 185-192.

320. Schmidtbleicher, D. & Buehrle, M. (1987). Neuronal adaptation andincrease of cross-sectional area studying different strength trainingmethods. In: Biomechanics X-B. Johnsson, B. (Ed.), Human Kinetics,Champaign, Ill., pp. 615-620.

321. Schmied, A., Ivarson, C. & Fetz, E.E. (1993). Short-termsynchronization of motor units in human extensor digitorum communismuscle: relation to contractile properties and voluntary control.Experimental Brain Research, 97: 159-172.

322. Schmied, A., Vedel, J.P. & Pagni, S. (1994). Human spinallateralization assessed from motoneurone synchronization: dependenceon handedness and motor unit type. Journal of Physiology, 480: 369-387.

323. Schwarzacher, H.G. (1959). Uber die Lange und AnordnundgerMuskelfasern in menschlichen Skeletmuskeln. Acta Anatomica, 37: 217-231.

324. Scott, S.H., Engstrom, C.M. & Loeb, G.E. (1993). Morphometry ofhuman thigh muscles. Determination of fascicle architecture by magneticresonance imaging. Journal of Anatomy, 182(Pt 2): 249-257.

325. Secher, N.H., Rorsgaard, S. & Secher, O. (1976). Contralateralinfluence on recruitment of type I muscle fibres during maximum voluntaryextension of the legs. Acta Physiological Scandinavica, 96: 20A-21A.

326. Secher, M.G., Rorsgaard, S. & Secher, O. (1978). Contralateralinfluence on recruitment of curarized muscle fibres during maximalvoluntary extension of the legs. Acta Physiological Scandinavica, 103:456-462.

327. Segal, R.L. (1992). Neuromuscular compartments in the human bicepsbrachii muscle. Neuroscience Letters, 140: 98-102.

328. Semmler, J.G. & Nordstrom, M.A. (1998). Motor unit discharge andforce tremor in skill- and strength-trained individuals. Experimental BrainResearch, 19: 27-38.

240

329. Sergio, L.E. & Ostry, D.J. (1995). Coordination of multiple musclesin two degree of freedom elbow movements. Experimental BrainResearch, 105: 123-137.

330. Sherwood, L. (1993). Human Physiology: From cells to systems. 2ndEd. West Publishing Company, MN, USA.

331. Signorile, J.F., Weber, B., Roll, B. Cariuso, J.F., Lowensteyen, I. &Perry, A.C. (1994). An electromyographical comparison of the squat andknee extension exercises. Journal of Strength and Conditioning Research,8: 178-183.

332. Simonsen, E.B., Thomsen, L. & Klausen, K. (1985). Activity of mono-and biarticular leg muscles during sprint running. European Journal ofPhysiology 54: 524-532.

333. Simoneau, J.A., Lortie, G., Boulay, M.R., Marcotte, M., Thibault, M.C. &Bouchard, C. (1985). Human skeletal muscle fiber type alteration withhigh-intensity intermittent training. European Journal of Applied Physiologyand Occupational Physiology, 54(3): 250-253.

334. Singh, M. & Karpovich, P.V. (1976). Isotonic and isometric forces offorearm flexors and extensors. Journal of Applied Physiology, 21: 1435-1437.

335. Sleivert, G.F., Backus, R.D. & Wenger, H.A. (1995). The influence of astrength-sprint training sequence on multi-joint power output. Medicine andScience in Sports and Exercise, 27(12): 1655-1665.

336. Smith, M. & Melton, P. (1981). Isokinetic versus isotonic variable-resistance training. American Journal of Sports Medicine, 9(4): 275-279.

337. Smith, R.C. & Rutherford, O.M. (1995). The role of metabolites instrength training. I. A comparison of eccentric and concentric contractions.European Journal of Applied Physiology & Occupational Physiology, 71(4):332-336.

338. Solomonow, M., Guzzi, A., Baratta, R., Shoji, H. & D'Ambrosia, R.(1986). EMG-force model of the elbows antagonistic muscle pair. Theeffect of joint position, gravity and recruitment. American Journal ofPhysical Medicine, 65(5): 223-244.

241

339. Srihari, T., Seedorf, U. & Pette, D. (1981). Ipsi- and contralateralchanges in rabbit soleus myosins by cross-innervation. European Journalof Physiology, 390(3): 246-249.

340. Staron, R.S, Karapondo, D.L., Kraemer, W.J., Fry, C.C., Gordon, S.E.,Falkel, J.E., Hagerman, F.C. & Hikida, R.S. (1994). Skeletal muscleadaptations during early phase of heavy-resistance training in men andwomen. Journal of Applied Physiology, 76: 1247-1255.

341. Staron, R.S., Malicky, E.S., Leonardi, M.J., Falkel, J.E., Hagerman,F.C. & Dudley, G.A. (1990). Muscle hypertrophy and fast fiber typeconversions in heavy resistance-trained women. European Journal ofApplied Physiology and Occupational Physiology, 60(1): 71-79.

342. Steele, J.R. & Brown, J.M.M. (1999). Effects of chronic anteriorcruciate ligament deficiency on muscle activation patterns during an abruptdeceleration task. Clinical Biomechanics, 14: 247-257.

343. Steiner, L.A., Harris, B.A. & Krebs, D.E. (1993). Reliability of eccentricisokinetic knee flexion and extension measurements. Archives of PhysicalMedicine and Rehabilitation, 74: 1327-1335.

344. Street, S.F. (1983). Lateral transmission of tension in frog myofibers: amyofibrillar network and transverse cytoskeletal connections are possibletransmitters. Journal of Cell Physiology, 114: 346-364.

345. Strojnik, V. (1995). Muscle activation level during maximal voluntaryeffort. European Journal of Applied Physiology and OccupationalPhysiology, 72(1/2): 144-149.

346. Suter, E., Herzog, W., Sokolosky, J., Wiley, J.P. & Macintosh, B.R.(1983). Muscle fiber type distribution as estimated by Cybex testing and bymuscle biopsy. Medicine and Science in Sports and Exercise, 25: 363-370.

347. Sweeney, H.L. & Stull, J.T. (1990). Alteration of cross-bridge kineticsby myosin light chain phosphorylation in rabbit skeletal muscle:implications for regulation of actin-myosin interaction. Proceedings of theNational Academy of Sciences of the United States of America, 87(1):414-418.

348. Tabary, J.C., Tabary, C., Tardieu, C., Tardieu, G. & Goldspink, G.

242

(1972). Physiological and structural changes in the cat’s soleus muscledue to immobilization at different lengths by plaster casts. Journal ofPhysiology, 224: 231-244.

349. Tamaki, T., Uchiyama, S. & Nakano, S. (1992). A weight-liftingexercise model for inducing hypertrophy in the hindlimb muscles of rats.Medicine and Science in Sports and Exercise, 24: 881-886.

350. Tanaguchi, Y. (1997). Laterality specificity in resistance training: theeffect of bilateral and unilateral training. European Journal of AppliedPhysiology, 75: 144-150.

351. Tanaka, H., Costill, D.L., Thomas, R.R., Fink, W.J. & Widrick, J.J.(1993). Dry-land resistance training for competitive swimming. Medicineand Science in Sports and Exercise, 25(8): 952-959.

352. Tanji, J. & Kato, M. (1973). Firing rate of individual motor units involuntary contraction of abductor digiti minimi muscle in man.Experimental Neurology, 40(3): 771-783.

353. Ter Haar Romeny, B.M., Denier Van Der Gon, J.J. & Gielen, C.C.A.M.(1984). Relation between location of a motor unit in the human bicepsbrachii and its critical firing levels for different tasks. ExperimentalNeurology, 85: 631-650.

354. Ter Haar Romeny, B.M., Denier Van Der Gon, J.J. & Geilen, C.C.A.M.(1982). Changes in recruitment order of motor units in the human bicepsmuscle. Experimental Neurology, 78: 360-368.

355. Tesch, P.A. & Larson, L. (1982). Muscle hypertrophy in bodybuilders.European Journal of Applied Physiology, 49: 301-306.

356. Tesch, P.A., Thorsson, A. & Essen-Gustavsson, B. (1989). Enzymeactivities of FT and ST muscle fibers in heavy-resistance trained athletes.Journal of Applied Physiology, 67(1): 83-87.

357. Tesch, P.A., Komi, P.V. & Häkkinen, K. (1987). Enzymatic adaptationsconsequent to long-term strength training. International Journal of SportsMedicine, 8(Suppl 1): 66-69.

358. Theeuwen, M., Gielen, C.C.A.M. & Miller, L.E. (1994). The relative

243

activation of muscles during isometric contractions and low-velocitymovements against a load. Experimental Brain Research, 101: 493-505.

359. Thépaut-Mathieu, C., van Hoeke, J. & Maton, B. (1988). Myoelectricaland mechanical changes linked to length specificity during isometrictraining. Journal of Applied Physiology, 64(4): 1500-1505.

360. Thorstensson, A., Sjodin, B. & Karlsson, J. (1975). Enzyme activitiesand muscle strength after “sprint training” in man. Acta PhysiologicaScandinavica, 94: 313-318.

361. Thorstensson, A., Karlsson, J., Biitasalo, J.H.T., Luhtanen, P. & KomiP.V. (1976). Effect of strength training on EMG of human skeletal muscle.Acta Physiologica Scandinavica, 98: 232-236.

362. Thusneyapan, S. & Zahalak, G.I. (1989). A practical electrode-arraymyoprocessor for surface electromyography. IEEE Transactions onBiomedical Engineering, 36(2): 295-299.

363. Tomberlin, J.P., Basford, J.R., Schwen, E.E., Orte, P.A., Scott, S.G.,Laughman, R.K. & Ilstrup, D.M. (1991). Comparative study of isokineticeccentric and concentric quadriceps training. Journal of Orthopaedic andSports Physical Therapy, 14(1): 31-36.

364. Tonndorf, M.L. & Hannam, A.G. (1994). Motor unit territory in relationto tendons in the human masseter muscle. Muscle Nerve 17: 436-443.

365. Tracey, B.L, Ivey, F.M., Hurlbut, D., Martel, G.F., Lemmer, J.T., Seigel,E.L., Metter, E.J., Fozzard, J.L., Fleg, J.L & Hurley, B.F. (1999). Musclequality II. Effects of strength training in 65-75-yr-old men and women.Journal of Applied Physiology, 86(1): 195-201.

366. Tsika, R.W., Herrick, R.E. & Baldwin, K.M. (1987). Time courseadaptations in rat skeletal muscle isomyosins during compensatory growthand regression. Journal of Applied Physiology, 63(5): 2111-2121.

367. Tupling, R., Green, H., Grant, S., Burnett, M. & Ranney, D. (2000).Postcontractile force depression in humans is associated with animpairment in SR Ca2+ pump function. American Journal of Physiology,278: 87-94.

244

368. Van Eijden, T.M.G.J. & Raadsheer, M.C. (1992). Heterogeneity offiber and sarcomere length in the human masseter muscle. TheAnatomical Record, 232: 78-84.

369. Van Eijden, T.M.G.J., Korfage, J.A.M & Brugman, P. (1997).Architecture of the human jaw-closing and jaw-opening muscles. TheAnatomical Record, 248: 464-474.

370. Van Gröeningen, C.J. & Erkelens, C.J. (1994). Task-dependentdifferences between mono- and bi-articular heads of the triceps brachiimuscle. Experimental Brain Research, 100(2): 345-52.

371. Van Leeuwen, J.L. & Spoor, C.W. (1996). A two dimensional model forthe prediction of muscle shape and intramuscular pressure. EuropeanJournal of Morphology, 34(1): 25-30.

372. Van Oteghen, S.L. (1973). Two speeds of isokinetic exercise as relatedto the vertical jump performance of women. Research Quarterly forExercise and Sport, 46: 78-84.

373. Van Soest, A.J., Schwab, A.L., Bobbert, M.F. & van Ingen Schenau,G.J. (1993). The influence of the biarticularity of the gastrocnemiusmuscle on vertical jumping achievement. Journal of Biomechanics, 26(1):1-8.

374. Van Soest, A.J., Roebroeck, M.E., Bobbert, M.F., Huijing, P.A. & VanIngen Schenau, G.J. (1985). A comparison of one-legged and two-leggedcountermovement jumps. Medicine and Science in Sports and Exercise,17(6): 635-639.

375. Van Zuylen, E.J., Gielen, C.C.A.M. & Denier Van Der Gon, J.J. (1988).Coordination and inhomogeneous activation of human arm muscles duringisometric torques. Journal of Neurophysiology, 60(5): 1523-1548.

376. Vandervoort, A.A., Sale, D.G. & Moroz, J. (1984). Comparison of motorunit activation during unilateral and bilateral leg extension. Journal ofApplied Physiology, 56(1): 46-51.

377. Viitasalo, J.T., Häkkinen, K. & Komi, P.V. (1981). Isometric anddynamic force production and muscle fibre composition in man. Journal ofHuman Movement Studies, 7: 199-209.

245

378. Vint, P.F. & Hinrichs, R.N. (1996). Differences between one-foot andtwo-foot vertical jump performances. Journal of Applied Biomechanics,12(3): 338-358.

379. Visser, J.J., Hoogkamer, J.E., Bobbert, M.F. & Huijing, P.A. (1990).Length and moment arm of human leg muscles as a function of knee andhip-joint angles. European Journal of Applied Physiology, 61: 453-460.

380. Voigt, M. & Klausen, K. (1990). Changes in muscle strength and speedon an unloaded movement after various training programmes. EuropeanJournal of Applied Physiology, 60: 370-376.

381. Voigt, M., Simonsen, E.B., Dyhre-Poulson, P. & Klausen.K. (1995).Mechanical and muscular factors influencing the performance in maximalvertical jumping after different prestretch loads. Journal of Biomechanics,28(3): 293-307.

382. Volek, J.S., Duncan, N.D., Mazzetti, S.A., Staron, R.S., Putukian, M.,Gomez, A.L, Pearson, D.R., Fink, W.J. & Kraemer, W.J. (1999).Performance and muscle fiber adaptations to creatine supplementationand heavy resistance training. Medicine and Science in Sports andExercise, 31(8): 1147-1156.

383. Walshe, A.D., Wilson, G.J. & Ettema, G.J.C. (1997). Stretch-shortencycle compared with isometric preload: contibutions to enhanced muscularperformance. Journal of Applied Physiology, 84(1): 97-106.

384. Walter, C.B. (1988). The influence of agonist premotor silence and thestretch-shortening cycle on contractile rate in active skeletal muscle.European Journal of Physiology, 57: 577-582.

385. Wang, N., Hikida, R.S., Staron, R.S. & Simoneau, J. (1993). Musclefibre types of women after resistance training – quantitative ultrastructureand enzyme activity. European Journal Physiology, 424: 494-502.

386. Weijs, W.A. & van der Wielen-Drent, T.K. (1982). Sarcomere lengthand EMG activity in some jaw muscles of the rabbit. Acta Anatomica, 113:178-188.

387. Weijs, W.A. & van der Wielen-Drent, T.K. (1983). The relationship

246

between sarcomere length and activation pattern in the rabbit masseter.Archives of Oral Biology, 28: 307-315.

388. Weir, J.P., Housh, D.J., Housh, T.J. & Weir, L.L. (1995a). The effect ofunilateral eccentric weight training and detraining on joint angle specificity,cross-training, and the bilateral deficit. Journal of Orthopaedic and SportsPhysical Therapy, 22(5): 207-215.

389. Weir, J.P., Housh, D.J., Housh, T.J. & Weir, L.L. (1997). The effect ofunilateral concentric weight training and detraining on joint anglespecificity, cross-training, and the bilateral deficit. Journal of Orthopaedic &Sports Physical Therapy. 25(4): 264-270.

390. Weir, J.P., Housh, T.J. & Weir, L.L. (1994). Electromyographicevaluation of joint angle specificity and cross-training after isometrictraining. Journal of Applied Physiology. 77(1): 197-201.

391. Weir, J.P., Housh, T.J., Weir, L.L. & Johnson, G.O. (1995b). Effects ofunilateral isometric strength training on joint angle specificity and cross-training. European Journal of Applied Physiology, 70: 337-343.

392. Whalen, R.G. (1985). Myosin isoenzymes as molecular markers formuscle physiology. Journal of Experimental Biology, 115:43-53.

393. Wickiewicz, T.L., Roy, R.R., Powell, P.L. & Edgerton, V.R. (1983).Muscle architecture of the human lower limb. Clinical Orthopaedics, 179:275-283.

394. Wickiewicz, T.L., Toy, R.R., Powell, P.L, Perrine, J.J. & Edgerton, V.R.(1984). Muscle architecture and force-velocity relationships in humans.Journal of Applied Physiology, 57(2): 435-443.

395. Wiemann, K. & Tidow, G. (1995). Relative activity of hip and kneeextensors in sprinting – implications for training. New Studies in Athletics,10(1): 29-49.

396. Wilhite, M.R., Cohen, E.R. & Wilhite, S.C. (1992). Reliability ofconcentric and eccentric measurements of quadriceps performance usingthe KIN-COM dynamometer: The effect of testing order for three differentspeeds. Journal of Sports Physical Therapy, 15(4): 175-182.

247

397. Willems, M.E.T. & Huijing, P.A. (1994). Heterogeneity of meansarcomere length in different fibres: effects of length range of active forceproduced in rat muscle. European Journal of Applied Physiology, 68: 489-496.

398. Williams, P., Watt, P., Bicik, V. & Goldspink, G. (1986). Effect of stretchcombined with electrical stimulation on the type of sarcomeres produced atthe ends of muscle fibers. Experimental Neurology, 93: 500-509.

399. Williams, P.E. (1990). Use of intermittent stretch in the prevention ofserial sarcomere loss in immobilised muscle. Annals of the RheumaticDiseases, 49: 316-317.

400. Willoughby, D.S. (1993). The effects of mesocycle-length weighttraining programs involving periodization and partially equated volumes onupper and lower body strength. Journal of Strength and ConditioningResearch, 7(1): 2-8.

401. Wilson, G.J. & Murphy, A.J. (1996). The use of isometric tests ofmuscular function in athletic assessment. Sports Medicine, 22(1):19-37.

402. Wilson, G.J., Murphy, A.J. & Walshe, A. (1996). The specificity ofstrength training: the effect of posture. European Journal of AppliedPhysiology, 73: 346-352.

403. Wilson, G.J., Newton, R.U., Murphy, A.J. & Humphries, B.J. (1993).The optimal training load for the development of dynamic athleticperformance. Medicine and Science in Sports and Exercise, 25(11): 1279-1286.

404. Wilson, G.J., Wood, G.A. & Elliott, B.C. (1991). The performanceaugmentation achieved from use of the stretch-shorten cycle: Theneuromuscular contribution. The Australian Journal of Science andMedicine in Sport, 23(4): 97-101.

405. Wottiez, R.D., Huijing, P.A. & Rozendal, R.H. (1983). Influence ofmuscle architecture on the length-force relation between form and functionof skeletal muscles. Journal of Morphology, 182: 95-113.

406. Wretengeng, P., Feng, Y. & Arborelius, U.P. (1996). High- and low-barsquatting techniques during weight-training. Medicine and Science inSports and Exercise, 28(2): 218-224.

248

407. Yao, W., Fuglevand, R.J. & Enoka, R.M. (2000). Motor-unitsynchronization increases EMG amplitude and decreases force steadinessof simulated contractions. Journal of Neurophysiology, 83(1): 441-452.

408. Yasuda, Y. & Miyamura, M. (1983). Cross transfer effects of musculartraining on blood flow in the ipsilateral and contralateral forearms.European Journal of Applied Physiology, 51: 321-329.

409. Young, A., Stokes, M. & Crowe, M. (1985). The size and strength of thequadriceps muscles of old and young men. Clinical Physiology, 5: 145-154.

410. Young, W. & Bilby, G.E. (1993). The effect of voluntary effort toinfluence speed of contraction on strength, muscular power, andhypertrophy development. Journal of Strength and Conditioning Research.7(3): 172-178.

411. Yue, G.H., Alexander, A.L., Laidlaw, D.H., Gmitro, A.F., Unger, E.C. &Enoka, R.M. (1994). Sensitivity of muscle proton spin-spin relaxation timeas an index of muscle activation. Journal of Applied Physiology, 77: 84-92.

412. Yue, G.H., Fuglevand, A.J., Nordstrom, M.A. & Enoka, R.M. (1995).Limitations of the surface-EMG technique for estimating motor unitsynchronization. Biology and Cybernetics, 73: 223-233.

413. Zuurbier, C.J. & Huijing, P.A. (1993). Changes in geometry of activelyshortening unipennate rat gastrocnemius muscle. Journal of Morphology,218(2): 167-80.

249

APPENDIX A

ETHICS APPLICATION

BIOMECHANICAL AND CROSS-SECTIONAL ANALYSIS OF

FOUR RESISTANCE TRAINING EXERCISES

250

Southern Cross University

Human Experimentation Ethics Committee

Proposed Project Using Experimental Procedures on HumanSubjects

INITIAL APPLICATION for approval for year 1997

1. Name of Project: Biomechanical and Cross-sectional Analysis of FourResistance Training Exercises

2. Name: Anthony Blazevich

Position: PhD Candidate

School: Exercise Science and Sport Management

Telephone Extension: 3231

3. Supervisor: Dr. Greg Wilson

4. Technicians associated with experiment:Mr. Robert BaglinMr. Mark Fisher

5. Funding - Have you received or applied for external funding of thisexperiment?

NO

6. Proposed date of commencement: September 15 1997.

7. Duration and estimated finishing date: October 31 1997.

8. Intended number of participants: 30 active male subjects, who haveexperience in weight training, will be voluntarily recruited from the Universityand local community.

9. Age range of participants: 18 - 30 yrs

10. Aim or purpose of the experiment: The purpose of the study is two-fold.The first purpose is to compare subject’s performances in several resistancetraining exercises with their performance in vertical jump, broad jump andsprint running tests. Resistance training exercises will include a reverse hacksquat (i.e. the subject performs a movement similar to a squat on a hacksquatmachine but faces the machine such that the body is prone but inclined to45o), barbell squat lift, Smith Machine squat lift and incline seated leg press

251

(hereafter referred to as leg press). The second purpose is to describe thekinetics, kinematics and electromyogram (EMG) patterns of the fourresistance training exercises. The movement pattern and EMG will then becompared to that of the running acceleration phase of sprint running and thevertical jump as described in the literature.

11. Methodology of the proposed study (including the source ofparticipants and how they were selected), procedures (e.g. blood samples),and methods to be adopted:

Thirty experienced male and female weight trainers who also perform trainingwhich includes running (eg soccer, hockey or rugby players, recreationalathletes, etc.) will be recruited from the University population and local area.The subjects will perform maximal lifts with a load equal to 80% of maximumon the reverse hack squat, barbell squat, Smith Machine squat and leg pressexercises as well as performing vertical jump, broad jump and 20 m sprinttests over three days. The vertical jump tests will include both squat jumpswith (counter-movement jump, CMJ) and without (squat jump, SJ) a counter-movement (i.e. a noticeable dip of the body before the vertical jump).Subjects will be asked to perform a training session three days prior to thefirst testing day to become familiar with the resistance training exercises.Training will involve two sets of ten repetitions of each of the resistanceexercises at a weight which could be lifted only ten times in each set.

On the first day of testing, subjects will perform each resistance trainingexercise at incremental weights until a weight cannot be lifted after a thoroughwarm-up including 5 minutes of cycling and several submaximum lifts. Thus,a measure of each subject’s maximum lift (1 RM - one repetition maximum)will be determined. On the second day of testing - two days after thedetermination of 1RM’s - subjects will perform two maximal SJ’s, CMJ’s and20 m sprints from a standing start. A third repetition will be performed if thesecond trial is greater than the first. On the third day, maximum lifts with eachof the four resistance exercises with 80% of each subject’s 1 RM will beperformed. Force will be recorded on a force platform which will be positionedeither under the feet (for the squat lifts) or on face of the weighted sledge (forthe leg press). The force platform will register zero force when the subject isstanding on the platform with the weight taken on the shoulders (or, for the legpress, while the subject is supporting the weight). Two trials will be allowed,but a third trial will be allowed if the second lift is greater than the first.

To minimise fatigue, four minutes of passive rest will be allowed betweeneach 1 RM and 80% of 1 RM trial and between the 30 m sprints, while twominutes rest will be allowed between successive jumps. Ten minutes of restwill be allowed between each testing block (i.e. between 1 RM tests on eachresistance exercise, and between the jumps and sprints). Subjects will beallowed to perform low intensity cycle exercise or jogging to aid recoveryduring this period. The order of testing will be randomised for each subject oneach day. This should ensure that effects of fatigue or familiarisation do notresult in a bias towards any one test.

252

During the testing period, ten male subjects will be randomly selected toparticipate in a biomechanical analysis of the resistance training movements.EMG data will be recorded from eight muscles (as described below) by bipolarsurface electrodes prior to a video analysis of the same movement.

(If there is insufficient space, an addendum should be attached)

12. Indicate any potential risk you can envisage to the participants andsafety precautions to be taken.

Subjects will be required to exert maximum effort during the testing sessionsand as such there is always the possibility that muscular strains can occur.However, only previously trained subjects are to be recruited as subjects andall subjects will be thoroughly warmed up prior to testing. Further, the testingwill be strictly supervised such that appropriate loads and techniques areemployed on all exercises. Dermal infection has also been reported afterplacement of EMG electrodes on the skin. To prevent infection, alcohol willbe applied to the skin prior to electrode placement and an antiseptic creamwill be applied to the skin after the electrodes have been removed.

13. Comment of any relevant ethical considerations, and attach theconsent form to be signed by participants, for approval.

The project is a standard cross-sectional and biomechanical study involvingtesting methods which are common practice and have been successfully andsafely performed by the investigator on a number of occasions.

A copy of the consent form to be signed by participants must be attached forapproval.

14. Comments (if thought necessary from Head of School e.g. onrelationship of this experiment to current practice in the discipline.

Signed Head of School: ________________________________

Date: ____________________

253

15. Certification:

I, the person responsible, certify that the proposed experiment will confirmwith the general principles set out in the N.H. and M.R.C. “Statement onHuman Experimentation and Supplementary Notes (1987)”.

Signed: _____________________________ Date: _____________

Supervisor: __________________________ Date: _____________

Approval of Committee on Ethics in Experimentation of Human Participants:

Signed: _____________________________ Date: ______________

Approval No: ________________________ Issued: ____________

254


FORM OF DISCLOSURE AND INFORMED CONSENT

Biomechanical and Cross-sectional Analysis of Four Resistance TrainingExercises

You are invited to participate in a study designed to compare subject’sperformances in four resistance training exercises (reverse hack squat,barbell squat, Smith Machine squat and leg press) with their performance invertical jump, broad jump and sprint running tests, and to describe the kinetics(forces), kinematics (motions) and electromyogram (EMG) patterns of the fourresistance training exercises. The movement pattern and EMG will then becompared to that of the running acceleration phase of sprint running and thevertical jump as described in the literature.

PROCEDURES TO BE FOLLOWEDAll testing will be carried out in the Biomechanics and Rehabilitation ResearchLaboratories of the School of Exercise Science and Sport Management. Afterperforming a training session three days prior to the first testing day tobecome familiar with the resistance training exercises, subjects will undergothree days of testing. On the first day of testing, subjects will perform eachresistance training exercise (the reverse hack squat, barbell squat, SmithMachine squat and leg press) at incremental weights until a weight cannot belifted. Thus, a measure of each subject’s maximum lift (1 RM - one repetitionmaximum) will be determined. On the second day of testing, two days afterthe determination of 1RM’s, subjects will perform two maximal SJ’s, CMJ’sand 20 m sprints from a standing start. A third repetition will be performed ifthe second trial is greater than the first. On the third day, maximum lifts witheach of the four resistance with 80% of their 1RM will be performed. Forcewill be recorded on a force platform which will be positioned either under thefeet (for the squat lifts) or on face of the weighted sledge (for the leg press).The force platform will register zero force when the subject is standing on theplatform with the weight taken on the shoulders (or, for the leg press, whilethe subject is supporting the weight). Two trials will be allowed, but a thirdtrial will be allowed if the second lift is greater than the first..

During the testing period, ten male subjects will be randomly selected toparticipate in a biomechanical analysis of the resistance training movements.EMG data will be recorded from eight muscles (as described below) by bipolarsurface electrodes prior to a video analysis of the same movement.Participation in the biomechanical analysis is not dependent uponparticipation in the cross-sectional analysis.

The above are standard tests of lower body strength and power. Further, thebiomechanical analysis is similar to that performed in numerous previousstudies. To minimise fatigue during the three days of testing, four minutes ofpassive rest will be allowed between each 1 RM and 80% of 1 RM trial and

255

between the 30 m sprints, while two minutes rest will be allowed betweensuccessive jumps. Ten minutes of rest will be allowed between each testingblock (i.e. between 1 RM tests on each resistance exercise, and between thejumps and sprints). Subjects will be allowed to perform low intensity cycleexercise or jogging to aid recovery during this period. The order of testing willbe randomised for each subject on each day. This should ensure that effectsof fatigue or familiarisation do not result in a bias towards any one test.

POSSIBLE SUBJECT DISCOMFORTS/RISKS

Subjects may experience some muscular soreness after the familiarisationand testing sessions. Further, the performance of maximal muscularcontractions, either during the testing or familiarisation sessions, has apotential to result in muscular strains. All necessary safe guards (includingproper warm-up and supervision) will be used to minimise such anoccurrence. Also, acute dermal infections have been reported after EMGelectrode use. To eliminate the chance of infection, an alcohol solution will beapplied to the skin prior to EMG electrode placement and an antiseptic creamwill be applied after EMG electrode removal.

SUBJECT BENEFITS

Subjects can benefit from participation in the study by:Having the opportunity to observe methods of experimental research in thisarea.Contributing to the advancement of science as a research participant.Obtaining information and advice on strength and power training.Being first to obtain the results and practical implications of the study.Having their lower body strength and power, and sprinting and jumpingabilities tested at no expense.

INVESTIGATOR RESPONSIBILITIES

Any information that is obtained in connection with this study and thatcan be identified with you will remain confidential and will be disclosed onlywith your permission.

If you decide to participate, you are free to withdraw your consent andto discontinue participation at any time without prejudice. However, priornotice of withdrawal would be appreciated.

If you have any questions, please contact Tony Blazevich on (H) 223 763 or(Uni) 203 231, at any time.

You will be given a copy of this form to keep.

256

SUBJECT’S DECLARATION OF CONSENT

I _________________________________ , being over eighteen years of ageconsent to being a subject in the research project “Biomechanical and Cross-sectional Analysis of Four Resistance Training Exercises”.

I have been given a copy of a “Form of Disclosure and Informed Consent”document which I fully understand describing the procedures to be followedand the consequences and risks involved in my participation as a subject.

I have read the information above and any questions I have asked have beenanswered to my satisfaction. I agree to participate in this activity, realisingthat I may withdraw without prejudice at any time.

I agree that research data gathered from the study may be published providedmy name is not used.

NAME OF SUBJECT ______________________________

SIGNATURE OF SUBJECT _________________________DATE ____________

NAME OF WITNESS ______________________________

SIGNATURE OF WITNESS _________________________DATE ____________

SIGNATURE OF RESEARCHER _____________________DATE ____________

certifying that the terms of the form have been verbally explained to thesubject, that the subject appears to understand the terms prior to signing theform, and that proper arrangements have been made for an interpreter whereEnglish is not the subjects first language.

257

APPENDIX B

ETHICS APPLICATION

INFLUENCE OF MOVEMENT PATTERN OF RESISTANCE

TRAINING EXERCISES ON VERTICAL JUMP AND SPRINT

RUNNING PERFORMANCE DURING CONCURRENT

RESISTANCE AND TASK TRAINING

258


Human Experimentation Ethics Committee

Proposed Project Using Experimental Procedures on HumanSubjects

INITIAL APPLICATION for approval for year 1999

1. Name of Project: Influence of movement pattern of resistance trainingexercises on vertical jump and sprint running performance during concurrentresistance and task training

2. Name: Anthony Blazevich

Position: PhD Candidate

School: Exercise Science and Sport Management

Telephone Extension: 3231

3. Supervisor: Dr. Robert Newton

4. Technicians associated with experiment:Mr. Robert BaglinMr. Mark Fischer

5. Funding - Have you received or applied for external funding of thisexperiment?Submitted full version to American Society of Biomechanics Graduate StudentGrant-in-aid scheme.

6. Proposed date of commencement: March 21, 1999.

7. Duration and estimated finishing date: June 1, 1999.

8. Intended number of participants: 60 active male subjects will bevoluntarily recruited from the University and local community.

9. Age range of participants: 18 - 30 yrs

Aim or purpose of the experiment: The present investigation will examine theperformance changes of complex tasks (vertical jump and acceleration phaseof a sprint run) while task training is performed with resistance training (eitherthe squat lift or a new forward hack squat exercise). In addition, performancechanges after concurrent task and resistance training will be compared toperformance changes of subjects performing no resistance training but twice

259

the number of task training sessions.

11. Methodology of the proposed study (including the source ofparticipants and how they were selected), procedures (e.g. blood samples),and methods to be adopted:

Experimental Design:Training will consist of a four-week familiarisation training phase in which allsubjects will perform sprint running (20 m) and vertical jump training twice aweek in addition to two resistance training sessions a week. The resistancetraining will consist of exercises that can be regarded as being non-specific tothe vertical jump and sprint running tasks. The familiarisation period willincorporate that period of training where substantial performanceimprovements in vertical jump and sprint running would occur. Thus, smallerimprovements are likely during the specific phase of training. The specificphase of training will last 6 weeks, short enough for minimal increases inhypertrophy to occur and for architectural (including sarcomere lengthchanges) and neural adaptations to be the most likely culprits for adaptation.During this phase of training, subjects will be organised into three traininggroups (2 experimental and 1 control), one group will dominantly use thesquat lift (or jump squat) and one group the one-legged forward hack squatduring their resistance training. Biomechanical analyses in our laboratoryhave compared and contrasted several versions of the vertical jump andsquat lift as well as examining the forward hack squat. Versions of theseexercises have been found that are very similar and could be deemedmovement pattern-specific. Other supplementary exercises will also beperformed during the training. Both of experimental groups will also performtwo vertical jump and sprint running sessions a week. The third, control,group will perform no resistance training but will participate in four verticaljump and sprint running sessions a week. Subjects will undergo a series oftests before and after this six-week specific training period.

Resistance TrainingDuring the ‘non-specific’ training phase, all subjects, including the controls,will perform resistance training twice a week with the dominant exercise beingthe leg press (incline). Other supplementary exercises will include the legextension, leg flexion (leg curl), deadlift and standing calf raise exercises.Four sets of leg press will be performed and two sets of all other exercises.Weights will be increased such that in week one, subjects will perform sets of12 repetitions and proceed to sets of 6 – 8 by the fourth week. Thus, allsubjects will perform general strengthening prior to the specific training phase.

During the ‘specific’ training phase, the two experimental groups will use their‘specific’ exercise as the dominant movement. Training will alternate suchthat the first session of each week is performed at weights of 80% of 1 RMwhile in the second session weights of 30% of 1 RM will be used. The ‘squat’group will perform the bilateral squat lift as their dominant exercise with all liftsbeing performed with a maximal concentric phase. As such, the exercisecould be likened to the jump squat since most subjects will leave the ground

260

at the end of the concentric phase. The eccentric phase will always beperformed over a 1 – 2 s period. In the first week, the subjects will perform 3sets of 6 repetitions of the squat exercise after 2 warm-up sets at increasingweights. Training will progress to 4 sets of 8 repetitions by the end of thetraining period. Supplementary training will include 3 sets of 10 repetitions ofprone back extension, 3 sets of 10 repetitions of leg curl and 3 sets of 10repetitions of the standing calf raise exercise. The group using the forwardhack squat exercise (‘FHS’) will perform the task unilaterally in training. Thus,while each leg might perform those repetitions in which they are directlyinvolved, synergist and fixator musculature will be involved in all repetitions.As such, training will be adjusted accordingly. In the first week, the subjectswill perform 2 sets of 6 repetitions on each leg after 2 warm-up sets atincreasing weights. Training will progress to 3 sets of 8 repetitions by the endof the training period. As for the squat group, all movements will beperformed with a maximal concentric phase with the weight being stopped atthe top of its movement by a spring to prevent injury. Supplementary trainingwill be identical to the squat group. Weights used by both groups will beincreased over the training period as their performances in these lifts improve.

Vertical Jump and Sprint Running Training

Experimental subjects will perform two sessions, while the control group willperform four session, each week. After a thorough warm-up, subjects willperform sets of 20 m sprint and vertical jumps. In the first session each week,sprint training will be performed first while in the second session verticaljumps will be performed first. This should eliminate the effects of fatigue onlearning and performance. In the first week, subjects will perform sessionsinvolving 3 x 30 m sprints and 3 sets of 3 countermovement jumps with oneminute rest between sets. By the end of the full 10 weeks of training, trainingwill increase to 6 x 30 m sprints and 6 sets of 4 countermovement jumps with4 minutes rest between sprints and 2 minutes rest between sets of jumps. Allsubjects will be briefed on the fundamentals of sprint running and verticaljumping during the familiarisation period.

261

Testing

Testing will be performed immediately prior and subsequent to the six weekspecific training phase with the test battery for each subject being spacedover several sessions to minimise fatigue.

1) Squat lift: squat lifts with a maximal concentric phase and an eccentricphase lasting 1 – 2 s will be performed on a force platform. Performancemeasures will include maximum force, time at which maximum force occurredand impulse during the concentric phase of the movement. In addition, bardisplacement will be registered by use of a flywheel instrument attached to thebar from which the concentric and eccentric phases can be discerned and barvelocity can be calculated. Subjects first perform a maximal isometric squatat the bottom position of a squat (individually determined at the point theirlowest point in a jump squat) and maximum force will be measured. Squat lifttesting will then be performed with weights equivAlént to 30% and 80% of thismaximum isometric force. By not performing lifts with maximum weight, therisk of injury should be dramatically reduced. Since the aim of the presentstudy is to investigate the effect of movement pattern, rather than velocity, oftraining exercises, testing after the 6 week training period will utilise thesesame weights, rather than a new weight that is congruent with subject’sstrength increases. Thus, subjects’ performances will be compared at a givenweight, similar to the vertical jump where weights are not changed aftertraining. Subjects will be allowed three attempts at each.2) Forward Hack Squat: after measuring subjects isometric force at thebottom of the forward hack squat movement, subjects will perform maximalone- and two-legged forward hack squats with a 1 – 2 s eccentric phase.Measures will be as per the squat lift. Subjects will be allowed three attemptsat each.3) Countermovement Vertical Jump: subjects will jump for maximumheight on a force platform. Ground reaction forces will be mearsured for eachjump from which body displacement will be estimated. Thus, problemsassociated with jump and reach tests will be eliminated. Subjects will performboth one- and two-legged trials; three repetitions will be performed of each.4) Sprint Test: 10 m and 20 m sprint times will be recorded during a 20 mmaximal sprint. Subjects will begin from a standing start with one foot in frontof the other but will be allowed to bend the knees to lower the body’s centre ofgravity. Subjects will be allowed three trials.5) Muscle Pennation and Thickness Tests: ultrasound will be used toimage the vastus lateralis and rectus femoris of subjects (10 subjects fromeach group only). For the rectus femoris, photographs will be taken at points20% and 50% of the distance from the tendomuscular junction (clearly visiblein most subjects) to its attachment at the hip. Thus measures of pennation,thickness and anatomical cross-sectional area will be taken at the midpointand at one end of the muscle. For vastus lateralis, photographs will be takenat 20% and 50% of the distance from the lateral condyle of the femur to thegreater trochanter.6) Electromyographic Analysis of the Vertical Jump and Sprint Run: Afterstandard skin preparation including hair removal, light abrasion with

262

sandpaper and swabbing with disinfecting alcohol, 8 subjects from each ofthe three groups will perform two-legged vertical jumps and 10 m sprints withelectrodes placed on their gluteus maximus, vastus lateralis, biceps femoris(long head), illiopsoas and rectus femoris muscles. Timing of musclecontractions and level of cocontraction will subsequently be estimated. Allsubjects will be filmed to ascertain key events during each task; an LED willbe used to synchronise EMG and video data.7) Isokinetic Knee Extension: To examine changes in the torque-anglerelationship about the knee, subjects will perform slow (30o.s-1) and fast(300o.s-1) isokinetic knee extensions. An isometric pre-load force will beimposed prior to the movement to minimise force spikes at the onset ofmovement and provide more reliable force measures in the early part of themovement. Biomechanical analyses suggest that the angle through which theknee moves differs between the squat and FHS exercises making this jointideal for torque-angle testing.

Statistical Analysis

After testing for normality of the data, repeated measures ANOVA’s with twofactors (group and time) will examine differences in performance from pre- topost-training. An Alpha Level of 0.05 will be used to minimise type I error.Correlation coefficients will also be calculated to examine relationshipsbetween test performances, and between changes in test performances andchanges in physiological variables (eg muscle thickness, pennation, level ofco-contraction, joint-specific torque, etc.).

12. Indicate any potential risk you can envisage to the participants andsafety precautions to be taken.

Subjects will be required to exert maximum effort during the testing sessionsand as such there is always the possibility that muscular strains can occur.However, only previously trained subjects are to be recruited as subjects andall subjects will be thoroughly warmed up prior to testing. Further, the testingwill be strictly supervised such that appropriate loads and techniques areemployed on all exercises. Dermal infection has also been reported afterplacement of EMG electrodes on the skin. To prevent infection, alcohol willbe applied to the skin prior to electrode placement and an antiseptic creamwill be applied to the skin after the electrodes have been removed.

13. Comment of any relevant ethical considerations, and attach theconsent form to be signed by participants, for approval.

The project is a standard training study involving testing methods which arecommon practice and have been successfully and safely performed by theinvestigator on a number of occasions.

263

14. Comments (if thought necessary from Head of School e.g. onrelationship of this experiment to current practice in the discipline.

Signed Head of School: ________________________________

Date: ____________________

15. Certification:

I, the person responsible, certify that the proposed experiment will confirmwith the general principles set out in the N.H. and M.R.C. “Statement onHuman Experimentation and Supplementary Notes (1987)”.

Signed: _____________________________ Date: ___________________

Supervisor: __________________________ Date: ___________________

Approval of Committee on Ethics in Experimentation of Human Participants:

Signed: _____________________________ Date: ___________________

Approval No: ________________________ Issued: __________________

264



Influence of movement pattern of resistance training exercises on verticaljump and sprint running performance during concurrent resistance and tasktraining

You are invited to participate in a study designed to examine the performancechanges of complex tasks (vertical jump and acceleration phase of a sprintrun) while task training is performed with resistance training (either the squatlift or a new forward hack squat exercise). In addition, performance changesafter concurrent task and resistance training will be compared to performancechanges of subjects performing no resistance training but twice the number oftask training sessions.

PROCEDURES TO BE FOLLOWED

Experimental Design:Training will consist of a four-week familiarisation training phase in which allsubjects will perform sprint running (20 m) and vertical jump training twice aweek in addition to two resistance training sessions a week. The resistancetraining will consist of exercises that can be regarded as being non-specific tothe vertical jump and sprint running tasks. The familiarisation period willincorporate that period of training where substantial performanceimprovements in vertical jump and sprint running would occur. Thus, smallerimprovements are likely during the specific phase of training. The specificphase of training will last 6 weeks, short enough for minimal increases inhypertrophy to occur and for architectural (including sarcomere lengthchanges) and neural adaptations to be the most likely culprits for adaptation.During this phase of training, subjects will be organised into three traininggroups (2 experimental and 1 control), one group will dominantly use thesquat lift (or jump squat) and one group the one-legged forward hack squatduring their resistance training. Biomechanical analyses in our laboratoryhave compared and contrasted several versions of the vertical jump andsquat lift as well as examining the forward hack squat. Versions of theseexercises have been found that are very similar and could be deemedmovement pattern-specific. Other supplementary exercises will also beperformed during the training. Both of experimental groups will also performtwo vertical jump and sprint running sessions a week. The third, control,group will perform no resistance training but will participate in four verticaljump and sprint running sessions a week. Subjects will undergo a series oftests before and after this six-week specific training period.

Resistance TrainingDuring the ‘non-specific’ training phase, all subjects, including the controls,will perform resistance training twice a week with the dominant exercise being

265

the leg press (incline). Other supplementary exercises will include the legextension, leg flexion (leg curl), deadlift and standing calf raise exercises.Four sets of leg press will be performed and two sets of all other exercises.Weights will be increased such that in week one, subjects will perform sets of12 repetitions and proceed to sets of 6 – 8 by the fourth week. Thus, allsubjects will perform general strengthening prior to the specific training phase.

During the ‘specific’ training phase, the two experimental groups will use their‘specific’ exercise as the dominant movement. Training will alternate suchthat the first session of each week is performed at weights of 80% of 1 RMwhile in the second session weights of 30% of 1 RM will be used. The ‘squat’group will perform the bilateral squat lift as their dominant exercise with all liftsbeing performed with a maximal concentric phase. As such, the exercisecould be likened to the jump squat since most subjects will leave the groundat the end of the concentric phase. The eccentric phase will always beperformed over a 1 – 2 s period. In the first week, the subjects will perform 3sets of 6 repetitions of the squat exercise after 2 warm-up sets at increasingweights. Training will progress to 4 sets of 8 repetitions by the end of thetraining period. Supplementary training will include 3 sets of 10 repetitions ofprone back extension, 3 sets of 10 repetitions of leg curl and 3 sets of 10repetitions of the standing calf raise exercise. The group using the forwardhack squat exercise (‘FHS’) will perform the task unilaterally in training. Thus,while each leg might perform those repetitions in which they are directlyinvolved, synergist and fixator musculature will be involved in all repetitions.As such, training will be adjusted accordingly. In the first week, the subjectswill perform 2 sets of 6 repetitions on each leg after 2 warm-up sets atincreasing weights. Training will progress to 3 sets of 8 repetitions by the endof the training period. As for the squat group, all movements will beperformed with a maximal concentric phase with the weight being stopped atthe top of its movement by a spring to prevent injury. Supplementary trainingwill be identical to the squat group. Weights used by both groups will beincreased over the training period as their performances in these lifts improve.

Vertical Jump and Sprint Running Training

Experimental subjects will perform two sessions, while the control group willperform four session, each week. After a thorough warm-up, subjects willperform sets of 20 m sprint and vertical jumps. In the first session each week,sprint training will be performed first while in the second session verticaljumps will be performed first. This should eliminate the effects of fatigue onlearning and performance. In the first week, subjects will perform sessionsinvolving 3 x 30 m sprints and 3 sets of 3 countermovement jumps with oneminute rest between sets. By the end of the full 10 weeks of training, trainingwill increase to 6 x 30 m sprints and 6 sets of 4 countermovement jumps with4 minutes rest between sprints and 2 minutes rest between sets of jumps. Allsubjects will be briefed on the fundamentals of sprint running and verticaljumping during the familiarisation period.

266

Testing

Testing will be performed immediately prior and subsequent to the six weekspecific training phase with the test battery for each subject being spacedover several sessions to minimise fatigue.

1) Squat lift: squat lifts with a maximal concentric phase and an eccentricphase lasting 1 – 2 s will be performed on a force platform. Performancemeasures will include maximum force, time at which maximum force occurredand impulse during the concentric phase of the movement. In addition, bardisplacement will be registered by use of a flywheel instrument attached to thebar from which the concentric and eccentric phases can be discerned and barvelocity can be calculated. Subjects first perform a maximal isometric squatat the bottom position of a squat (individually determined at the point theirlowest point in a jump squat) and maximum force will be measured. Squat lifttesting will then be performed with weights equivalent to 30% and 80% of thismaximum isometric force. Since the aim of the present study is to investigatethe effect of movement pattern, rather than velocity, of training exercises,testing after the 6 week training period will utilise these same weights, ratherthan a new weight that is congruent with subject’s strength increases. Thus,subjects’ performances will be compared at a given weight, similar to thevertical jump where weights are not changed after training. Subjects will beallowed three attempts at each.2) Forward Hack Squat: after measuring subjects isometric force at thebottom of the forward hack squat movement, subjects will perform maximalone- and two-legged forward hack squats with a 1 – 2 s eccentric phase.Measures will be as per the squat lift. Subjects will be allowed three attemptsat each.3) Countermovement Vertical Jump: subjects will jump for maximumheight on a force platform. Ground reaction forces will be measured for eachjump from which body displacement will be estimated. Thus, problemsassociated with jump and reach tests will be eliminated. Subjects will performboth one- and two-legged trials; three repetitions will be performed of each.4) Sprint Test: 10 m and 20 m sprint times will be recorded during a 20 mmaximal sprint. Subjects will begin from a standing start with one foot in frontof the other but will be allowed to bend the knees to lower the body’s centre ofgravity. Subjects will be allowed three trials.5) Muscle Pennation and Thickness Tests: ultrasound will be used toimage the vastus lateralis and rectus femoris of subjects (10 subjects fromeach group only). For the rectus femoris, photographs will be taken at points20% and 50% of the distance from the tendomuscular junction (clearly visiblein most subjects) to its attachment at the hip. Thus measures of pennation,thickness and anatomical cross-sectional area will be taken at the midpointand at one end of the muscle. For vastus lateralis, photographs will be takenat 20% and 50% of the distance from the lateral condyle of the femur to thegreater trochanter.6) Electromyographic Analysis of the Vertical Jump and Sprint Run: 8subjects from each of the three groups will perform two-legged vertical jumpsand 10 m sprints while electrodes are placed on the gluteus maximus, vastus

267

lateralis, biceps femoris (long head), illiopsoas and rectus femoris muscles.Timing of muscle contractions and level of cocontraction will subsequently beestimated. All subjects will be filmed to ascertain key events during eachtask; an LED will be used to synchronise EMG and video data.7) Isokinetic Knee Extension: To examine changes in the torque-anglerelationship about the knee, subjects will perform slow (30o.s-1) and fast(300o.s-1) isokinetic knee extensions. An isometric pre-load force will beimposed prior to the movement to minimise force spikes at the onset ofmovement and provide more reliable force measures in the early part of themovement. Biomechanical analyses suggest that the angle through which theknee moves differs between the squat and FHS exercises making this jointideal for torque-angle testing.


Subjects may experience some muscular soreness after the familiarisationand testing sessions. Further, the performance of maximal muscularcontractions, either during the testing or training sessions, has a potential toresult in muscular strains. All necessary safe guards (including proper warm-up and supervision) will be used to minimise such an occurrence. Also, acutedermal infections have been reported after EMG electrode use. To eliminatethe chance of infection, an alcohol solution will be applied to the skin prior toEMG electrode placement and an antiseptic cream will be applied after EMGelectrode removal.

SUBJECT BENEFITS

Subjects can benefit from participation in the study by:Opportunity to improve speed and strength by taking part in a supervised,periodised training regime.Being tested on two occasions to determine level of training and rate ofimprovement.Free use of an air conditioned gym for training.Obtaining information and advice on strength and power training.Having the opportunity to observe methods of experimental research in thisarea.Contributing to the advancement of science as a research participant.Being first to obtain the results and practical implications of the study.




If you have any questions, please contact Tony Blazevich on (H) 216 617 or

268

(Uni) 203 231, at any time.


269


I _________________________________ , being over eighteen years of ageconsent to being a subject in the research project “Influence of movementpattern of resistance training exercises on vertical jump and sprint runningperformance during concurrent resistance and task training”.

I have been given a copy of a “Form of Disclosure and Informed Consent”document which I fully understand describing the procedures to be followedand the consequences and risks involved in my participation as a subject.



NAME OF SUBJECT ______________________________


NAME OF WITNESS ______________________________




270

APPENDIX C

STATEMENT OF INFORMED CONSENT

RELIABILITY AND VALIDITY OF ISOMETRIC SQUAT AND

FORWARD HACK SQUAT TESTS

271



Reliability and validity of isometric squat and forward hack squattests.

You are invited to participate in a study designed to examine the reliability andvalidity of isometric squat and forward hack squat tests.

PROCEDURES TO BE FOLLOWED

Experimental Design:

Subjects will attend two 45-min testing sessions. Each session will involve 3isometric squat lifts, 3 isometric forward hack squat (FHS) lifts, and theperformance of 1 repetition maximum (1 RM) of either the squat or FHS.

Testing

Squat: Subjects will stand under an immoveable bar with a knee angleof 90o and the bar resting across the shoulders. When instructed, subjectswill push upward against the bar with maximal exertion. Force producedduring the push will be recorded by force platform.

FHS: Subjects will position themselves on the FHS machine with aknee angle of 90o and a hip angle of 110o. When instructed, the subjects willpush upward against shoulder pads that are immoveable. Force producedduring the push will be recorded by load cell.

1 RM squat: After warm up including several repetitions of submaximal squatlifts, subjects will perform single squat lifts with the weight being increasedincrementally until the weight cannot be lifted. Metal stops will prevent the barand weights from moving below a predetermined level to minimise injury risk.The maximum weight lifted will be taken as that subject’s 1 RM.

1 RM FHS: After warm up including several repetitions of submaximal FHSlifts, subjects will perform single FHS lifts with the weight being increasedincrementally until the weight cannot be lifted. Metal stops will prevent thesled and weights from moving below a predetermined level to minimise injuryrisk. The maximum weight lifted will be taken as that subject’s 1 RM.

Following the testing, reliability of the isometric lifts will be calculated, and therelationship between isometric and 1 RM strength will be determined.

272


Subjects may experience some muscular soreness after the testing sessions.Further, the performance of maximal muscular contractions can potentiallyresult in muscular strains. All necessary safe guards (including proper warm-up and supervision) will be used to minimise such an occurrence.

SUBJECT BENEFITS

Subjects can benefit from participation in the study by:Obtaining information and advice on strength and power training.Having the opportunity to observe methods of experimental research in thisarea.Contributing to the advancement of science as a research participant.




If you have any questions, please contact Tony Blazevich on (Uni) 66 203231, at any time.


273


I _________________________________ , being over eighteen years of ageconsent to being a subject in the research project “Reliability and validity ofisometric squat and forward hack squat tests.”.

I have been given a copy of a “Form of Disclosure and Informed Consent”document that I fully understand describing the procedures to be followed andthe consequences and risks involved in my participation as a subject.



NAME OF SUBJECT ______________________________


NAME OF WITNESS ______________________________




274

APPENDIX D

TRAINING PROGRAMS

EXAMPLE RESISTANCE TRAINING PROGRAMS FOR SQ

(SQUAT) AND FHS (FORWARD HACK SQUAT) GROUPS

275

Gym Training ProgramName: Person ATraining Group: SquatPredicted Maximum: 189.12 kg

Weights for Heavy Sessions should range from approximately:Week 1 85.96 – 107.46 kgWeek 5 128.95 – 150.44 kg

Weights for Explosive Sessions should range from approximately:Week 1 42.98 – 64.47 kgWeek 5 64.47 – 85.96 kg

Heavy day program:

Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 40 kg, 8 repsSet 1, 30 - 40% of max. predicted = 60 - 85 kg, 8 repsSet 2, use weight in range above (heavy) = 6 repsSet 3, use weight in range above = 6 repsSet 4, use weight in range above = 6 reps

2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (heavy and controlled)2 - 3 sets of 8 calf raises (heavy and controlled)

Light day program:

Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 40 kg, 8 repsSet 1, 30 - 40% of max. predicted = 60 - 85 kg, 8 repsSet 2, use weight in range above (light) = 6 repsSet 3, use weight in range above = 6 repsSet 4, use weight in range above = 6 reps

2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (slightly lighter and faster)2 - 3 sets of 8 calf raises (slightly lighter and faster, slow down, fastup)

276

Gym Training ProgramName: Person BTraining Group: Forward Hack SquatPredicted Maximum: 103.65 kg

Weights for Heavy Sessions should range from approximately:Week 1 14.53 – 32.35 kgWeek 5 50.18 – 68.00 kg

Weights for Explosive Sessions should range from approximately:Week 1 0 kgWeek 5 0 – 14.5 kg

Heavy day program:

Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 0kg, 8 repsSet 1, 30 - 40% of max. predicted = 0 kg, 8 repsSet 2, use weight in range above (heavy) = 6 repsSet 3, use weight in range above = 6 reps

2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (heavy and controlled)2 - 3 sets of 8 calf raises (heavy and controlled)

Light day program:

Warm-up on squats bar only, 8 repsWarm-up on squats, 20% of max. predicted = 0 kg, 8 repsSet 1, 30 - 40% of max. predicted = 0 kg, 8 repsSet 2, use weight in range above (light) = 6 repsSet 3, use weight in range above = 6 reps

2 sets of 10 repetitions of back extension (use weights if required)3 sets of 8 repetitions of leg curl (slightly lighter and faster)2 - 3 sets of 8 calf raises (slightly lighter and faster, slow down, fastup)

277

APPENDIX F

RELIABILITY STUDY

A COMPARISON OF DIGITAL CURVIMETER AND

MATHEMATICAL ESTIMATES OF FASCICLE LENGTH IN

CONTRACTING MUSCLE.

278

ABSTRACT

Fascicle length can be measured in vivo by ultrasound techniques, although

two methods of estimating fascicle length are currently used: mathematical

estimation and curvimeter measurement. The purpose of this study was to

first to determine if significant differences exist between fascicle length

measures estimated by mathematical and curvimeter methods, and second to

examine the reliability of the mathematical procedure relative to the

curvimeter procedure. Photographs of up to nine sites on the gastrocnemius

medialis muscle of six subjects were taken using ultrasound imaging.

Photographs were taken in both relaxed and contracted (plantarflexion at 50%

of maximum) conditions and muscle thickness, pennation and fascicle length

subsequently measured. Differences between mathematical and curvimeter

estimates of fascicle length were examined by multilevel regression analysis.

There was no significant difference between fascicle length measures

estimated by the two methods, although differences were greater for the

relaxed and relaxed-contracted (change in fascicle length from relaxed to

contracted state) conditions compared to the contracted condition. Reliability

of single estimates were high for the curvimeter method (Intraclass

correlations [ICC’s] = 0.75 – 0.91) but low for mathematical estimation (ICC’s

= 0.39 – 0.60). Nonetheless, by averaging a number (N=9) of repeated

measurements on the subjects, reliability of the mathematical method was

increased significantly (ICC’s = 0.85 – 0.93). These results suggest that, for

the gastrocnemius medialis muscle, there was little difference between

fascicle length estimated by mathematical or curvimeter methods although the

reliability of mathematical estimates was very low, and statistical power would

be dramatically reduced. Nonetheless, reliability of a number of repeated

measurements was high and comparable to the curvimeter method.

279

INTRODUCTION

Muscle contraction properties are strongly influenced by architectural

characteristics such as muscle size, pennation (fibre angle relative to the

tendon or aponeurosis) and fibre length. For example, muscles that are often

recruited to perform high force, low velocity contractions tend to have shorter

fibres and greater pennation while muscles recruited during rapid contractions

have longer fibres and lesser pennation (Burkholder et al., 1994; Kawakami et

al., 1995; Kumagai et al., 2000). Assessing inter-individual differences and

longitudinal changes in muscle architecture aids our understanding of the

muscular system. Moreover, knowledge of muscle architecture during

contraction is important for the development of realistic muscle models. Since

pennation and fibre length change during contraction, muscle models that

incorporate only architectural parameters of relaxed muscle are prone to

prediction errors. Therefore, knowledge of muscle architecture both at rest

and during contraction can allow researchers to better predict the functional

properties of human muscle.

Muscle architecture has been studied in both resting (Kumagai et al., 2000;

Van Eijden et al., 1997) and contracting (Herbert & Gandevia, 1995;

Kawakami et al., 1998; Narici et al., 1996) muscle. Such research has

examined how exercise affects architecture (Henriksson-Larsén et al., 1992;

Kawakami et al., 1993, 1995; Kumagai et al., 2000) and how architecture

changes during muscle contraction (Herbert & Gandevia, 1995; Narici et al.,

1996). While there are recognised methods of measuring muscle size and

pennation, methods for measuring fibre length are not consistent. The fibre

length of many human muscles is synonymous with the length of the fascicles

that encase fibre bundles. Since fascicles can be clearly visualised using

ultrasound imaging, fascicle length can be estimated from ultrasound

photographs.

Nonetheless, fascicle length can be estimated by two different methods. First,

280

fascicle length can be estimated mathematically by the equation:

FL = MT/sin θ

where FL is the fascicle length, MT the muscle thickness, and θ the angle of

muscle pennation. Prediction of fibre length from fascicle length by this

method has been used extensively in past research (Henriksson-Larsén et

al., 1992; Kawakami et al., 1995; Kumagai et al., 2000). However, this

method incorrectly assumes that fascicles are linear within the muscle. More

recently, researchers have captured entire fascicles on ultrasound images

and used a digital curvimeter (Comcurve-8, Koizumi, Japan) to more directly

measure fascicle length (Fukunaga et al., 1997; Kawakami et al., 1998, 2000).

Here, the ultrasound images are printed onto calibrated recording film (SSZ-

305, Aloka) and the length of fascicles measured by a curvimeter. The

advantage of this method is that the curve of the fascicle is accounted for.

Thus, compared to mathematical estimation, it can be considered that the

measures of fascicle length by digital curvimeter are truer.

Unfortunately, digital curvimeter procedures have not been used in many

previous studies. Nonetheless, it is unclear how reliable current mathematical

estimation procedures are given fascicle curvature is not accounted for.

Furthermore, no research has compared fascicle length measures obtained

by the two methods. The purpose of the present study therefore was two-fold,

first to determine if a significant difference exists between fascicle length

values estimated by the two methods in both relaxed and contracted muscle,

and second to examine the reliability of the mathematical procedure relative to

the digital curvimeter procedure.

281

METHODS

Measurement of Muscle Architecture

Previously published measures of fascicle length, fascicle angle (pennation)

and muscle thickness of the human gastrocnemius medialis (GM) (Kawakami

et al., 2000) were reanalysed to calculate mathematical estimates of fascicle

length. Methods used to measure muscle architecture are presented in

Kawakami et al. (2000), however a summary of the methods will be presented

here. B-mode ultrasonography was used to view images of GM in a two-

dimensional plane while six male subjects lay prone with their knee extended

and ankle at 90o. Each subject’s foot was firmly attached to an electric

dynamometer (Myoret, Asics) and the lower leg fixed to a test bench.

Measurements were taken for two conditions, with the gastrocnemius relaxed

and while performing isometric plantar flexion at a level of 50% of maximum

voluntary force. Plantar flexor torque was recorded from the output of the

dynamometer by a computer (PC-9801, NEC). It was assumed that there

was no muscle activity in the passive condition.

In both relaxed and contracted conditions, ultrasound images were obtained

from up to nine sites on GM. Longitudinal ultrasonic images of GM were

obtained at each site such that the echoes from interspaces of fascicles and

from the superficial and deep aponeuroses were visualised (Figure 1). The

ultrasonic images were then printed onto calibrated recording films (SSZ-305,

Aloka). The plane of the ultrasonogram was deemed parallel to the fascicles

since the fascicles could be followed from superficial to deep aponeurosis

(Kawakami et al., 1993). In the printed images, the length of the fascicles and

fascicle angles (pennation) were measured. Fascicle length was measured

by the use of a digital curvimeter (Comcurve-8, Koizumi) which allowed the

somewhat curved fascicles to be measured directly. Reliability of fascicle

length measures using the digital curvimeter has been previously established

(Fukunaga et al., 1997). Fascicle angle was measured with a protractor after

282

a line was drawn tangentially to the fascicle at the contacting point onto the

aponeurosis. The angle made by the line and aponeurosis was measured as

the fascicle angle. At each point, muscle thickness was also measured.

Muscle thickness was defined as the distance from the junction of the adipose

and muscle boundaries to the internal aponeurosis. From measures of

muscle thickness and fascicle angle at each of the eight sites, fascicle length

was also mathematically estimated (FL = MT/sin θ, where FL is the fascicle

length, MT the muscle thickness, and θ the angle of muscle pennation).

Values for fascicle length using the two methods (digital curvimeter versus

mathematical estimation) were then compared.

A

B

Muscle/adiposeboundary

Fascicle

Aponeurosis

Musclethickness

Figure 1. Ultrasound photographs of gastrocnemius medialis under relaxed (A) andcontracted (B; 50% MVC) conditions. When contracted, muscle thickness and fasciclelength decrease compared to the relaxed state. Digital curvimeter estimates of fasciclelength are performed by tracing a fascicle from the aponeurosis to the muscle/adiposeboundary. For the mathematical method, fascicle length is estimated by the formula FL =MT/sin θ, where FL is the fascicle length, MT the muscle thickness, and θ the angle ofmuscle pennation (angle between the fascicle and aponeurosis).

B

A

283

Data Analysis

Description of data

The change in fascicle length from the relaxed (A) to contracted (B) state was

designated ‘relaxed-contracted (C)’. There were eight repeated measures

(replicates) on two subjects and nine repeated measures (replicates) on the

other four subjects. Although Kawakami et al. (2000) found systematic

variation among these repeated measures, for present purposes they were

treated as randomly varying replicates. Corresponding to the curvimeter-

measured data (mFL; measured fascicle length), fascicle lengths were

estimated by the equation presented previously to construct a completely

parallel ‘estimated fascicle length’ (estFL) data set.

Data Analysis

Hierarchical (multilevel) linear regression models were fitted to the data.

(Goldstein, 1995; Hox, 1994; Snijders and Bosker, 1999). The residuals

about the fixed parts of the models (overall constant and any explanatory

factors) were modeled as varying randomly at the replicate within subject (e0ij)

and subject (u0j) levels. Restricted maximum likelihood estimates were

obtained to correct for the downward bias of maximum likelihood estimates of

variance components (Snijders and Bosker, 1999, p.56).

Three sets of three analyses (A1 to C3) were performed. For each of the sets

of relaxed (A), contracted (B) and relaxed-contracted (C) data, analyses were

performed on the measured lengths (A1,B1,C1), the estimated lengths

(A2,B2,C2) and the relationship between the measured and estimated lengths

(A3,B3,C3). The analyses A and B were variance components models in

which no explanatory variables (other than the overall intercepts) were fitted,

but in analyses C the measured values were regressed on the estimated

284

values. The purpose of the analyses A and B was to estimate the

reliabilities of the measured and estimated lengths, while the purpose of the

analyses C was to estimate the ‘predictability’ of measured from the estimated

lengths.

Three subsidiary analyses (two-level variance components models) - one

each for relaxed, contracted and relaxed-contracted muscle - were performed

on the measurement-estimate difference scores in order to estimate the

extent to which the estimates were high (overestimates) or low

(underestimates) relative to the digital curvimeter measurements.

Two measures of reliability were determined for variance components

(intercept only) models: the intraclass correlation coefficient (ICC = ρ1)

measuring the reliability of a single replicate and ρ2 measuring the reliability of

the mean of n level 1 units as a measure of a level 2 unit (mean of a number

of replicates as a measure of subject fascicle length). Measures of reliability

were calculated according to the formulae presented in Snijders and Bosker

(1999, pp.24-26; n=9 in the present analyses). Two measures of explained

variance are reported for models with explanatory variables: R12 and R2

2

measuring the proportional reductions in mean squared prediction errors at

levels 1 and 2 respectively due to the explanatory variables, calculated

according to the formulae presented in Snijders and Bosker (1999, pp.102-

103).

285

RESULTS

Results are presented in Table 1. An explanation of abbreviations is provided

below the table. Due to the length of the table, it is presented at the end of

this paper.

Comparison of Measured and Estimated Fascicle Length

Error-bar plots showing the subjects means and 95% confidence intervals for

the measured and estimated fascicle length are presented in Figure 2. For

relaxed, contracted and relaxed-contracted muscle, estimated fascicle length

underestimated the digital curvimeter measurements. The average

underestimation ranged from 0.43mm (1.2%) for contracted muscle, through

1.02mm (1.8%) for relaxed muscle to 1.21 (3.2%) for relaxed-contracted

muscle. These difference estimates correspond closely to the absolute

differences in the sizes of the β0ij parameter estimates from the A1-A2, B1-B2,

and C1-C2 pairs of analyses, as reported in Table 1. In no case were the

underestimates significant. t-values (parameter estimate / standard error)

ranged from 0.51 for relaxed-contracted, 0.58 for contracted and 1.03 for

relaxed muscle.

Relationship between the Estimates and the Measurements

The analyses A3, B3 and C3 found highly significant relationships between

the estimates and the measurements for each of the relaxed, contracted and

relaxed-contracted muscle fascicle lengths (the β1 estimates from Table 1).

However, although highly significant, the effects were far smaller than might

be expected of the relationship between reliable estimates and their

corresponding measurements. At the replicate level, the proportional

reductions in the mean squared prediction errors R-squared measure range

from 0.18 for relaxed-contracted, through 0.20 for relaxed to 0.22 for

contracted muscle. At the subject level, the proportional reductions in mean

286

squared prediction errors were slightly higher at 0.20, 0.21 and 0.23

respectively. These relatively small proportions of the total variation among

the measurements ‘explained by’ the estimated fascicle length values are due

mostly to the variability or unreliability of these estimates.

Variance Components and Reliability

The proportions of total variance for the measurements at the subject level –

Figure 2. Mean fascicle lengths (with 95%confidence intervals) for measured ("") andestimated (ï) relaxed, contracted andrelaxed-contracted fascicle lengths.Estimated fascicle lengths were generallyshorter (not significant) and more variablethan measured fascicle lengths.

287

the intraclass correlations (ICC’s) or reliabilities of measurement at the

subject level from a single, randomly selected replicate (ρ1’s) - range from

0.75 for relaxed-contracted, 0.90 for relaxed and 0.91 for contracted muscle.

Although 0.75 is somewhat lower than ideal, this would be an acceptable level

of measurement reliability for some research. In contrast, the proportions of

total variance for estimated fascicle length at the subject level range from 0.39

for relaxed-contracted, 0.48 for relaxed and 0.60 for contracted muscle.

Apart, perhaps, for the 0.60 estimate for contracted muscle, these are less

than acceptable levels of measurement reliability, with adverse effects on

statistical power and contributing to production of inconsistent findings in

research on small samples.

These reliability estimates might be lower than the values of reliability for true

replicates because the ‘replicates’ here were expected to vary systematically

to some degree (since measures were taken from different regions within the

muscle rather than at one site). Nonetheless, the unreliability of the estimates

relative to the measurements is clear in the comparisons of their respective

amounts of replicate variation: ie 57.1 to 5.4 for relaxed, 21.4 to 3.1 for

contracted and 59.7 to 11.2 for relaxed-contracted.

Whilst single estimates provide unacceptably low levels of measurement

reliability at the subject level (ICC’s = ρ1’s), the means of a number of

replicates (ρ2’s) possess quite acceptable reliabilities. These were calculated

on the basis of 9 replicates (the mode in the present data) and ranged from

0.85 for relaxed-contracted, through 0.89 for relaxed and to 0.93 for

contracted muscle.

288

DISCUSSION

Average estimated fascicle length (estFL; mathematical method) was less

than measured fascicle length (mFL; curvimeter method) for all conditions

(relaxed, contracted and relaxed-contracted muscle) with differences ranging

from approximately 0.4 to 1.2 mm (1.2 – 3.2%). None of these differences

were statistically significant. Whether underestimation of this order is

substantively important will depend upon the context of the particular

research, but the small number of subjects and low statistical power would

have influenced its significance here. In the present study however, there

was no significant difference in fascicle length measures between the two

methods.

Nonetheless, differences between estFL and mFL were greater for relaxed

than contracted muscle. While small, the difference is likely to be related to

the length of fascicles in these muscle states. Fascicles are longer in relaxed

than contracted muscle. For a given relative difference in fascicle lengths

determined by the two methods, the absolute difference will be greater than in

contracted muscle. The difference between estFL and mFL was greatest

when fascicle length change from relaxed to contracted states was estimated

(1.2 mm or 3.2% of average fascicle length). When measures of fascicle

length in relaxed and contracted muscle were used to determine the change

in fascicle length, there was a summation effect culminating in greater

differences between the two methods. Thus, for the gastrocnemius medialis

muscle, there was no significant difference between fascicle length

determined by digital curvimeter and mathematical methods, although in

muscle with long fascicles the difference between the methods would be

greater and the difference between muscles might be significant.

There was also no statistically significant difference between the measured

fascicle lengths and those predicted from the regression of measured fascicle

lengths on estimated fascicle lengths for relaxed, contracted and relaxed-

289

contracted muscle. Nonetheless, for repeated measures at each section of

the muscle, the proportional reductions in the mean squared prediction errors

R-squared measures ranged from 0.18 for relaxed-contracted, through 0.20

for relaxed to 0.22 for contracted muscle. When measures at different sites of

the muscle were averaged for each subject, the proportional reductions in

mean squared prediction errors were slightly higher at 0.20, 0.21 and 0.23

respectively. While these relatively small proportions of the total variation

among the measurements ‘explained by’ estFL were due largely to the

variability or unreliability of these estimates (see below), approximately 80%

of the total variance was left unexplained. Thus, despite mFL being predicted

well by estFL in the present study, there were clearly other factors affecting

the prediction of mFL besides estFL variability.

Reliability of the Measures

The reliability of digital curvimeter measurements at the subject level from a

single, randomly selected replicate (ρ1’s) on the gastrocnemius was

calculated. ICC’s were 0.91. 0.90 and 0.75 for contracted, relaxed and

relaxed-contracted conditions respectively. These reliability estimates might

be lower than the values of reliability for true replicates because the

‘replicates’ here were expected to vary systematically to some degree (since

measures were taken from different regions within the muscle rather than at

one site). Nonetheless, ICC’s for fascicle length determined mathematically

were 0.60, 0.48 and 0.39 for contracted, relaxed and relaxed-contracted

conditions respectively. The unreliability of estFL relative to mFL was further

highlighted by the comparisons of their respective amounts of replicate

variation: ie 57.1 to 5.4 for relaxed, 21.4 to 3.1 for contracted and 59.7 to 11.2

for relaxed-contracted. Thus, again, variability of mathematical estimation

was far greater than for the curvimeter method. Such reliability is less than

acceptable and would adversely affect statistical power and contribute to

inconsistent findings in research on small samples.

290

Increasing the Reliability of Mathematically Estimated Fascicle Lengths

Whilst single estimates provide unacceptably low levels of measurement

reliability at the subject level (ICC’s = ρ1’s), the means of a number of

replicates (ρ2’s) possessed quite acceptable reliabilities. ICC’s for the

average fascicle length of a subject ranged from 0.85 for relaxed-contracted,

through 0.89 for relaxed and to 0.93 for contracted muscle. This suggests a

remedy in terms of averaging repeated measurements on the same region of

muscle (replicates) within subjects and conditions. As Table 1 shows,

although reliabilities at the replicate level (ICC = ρ1) vary between only 0.39

and 0.60, the reliabilities of averages of 9 replicates as measures at the

subject level (ρ2) range between 0.85 and 0.93. The minimum number of

replicates (nmin) required to yield a desired level of reliability at the subject

level (ρ2) given the reliability of an estimate at the replicate level (ρ1) is given

by Snijders and Bosker (1999, p.144) as,

nmin = ρ2(1-ρ1) / ρ1 (1-ρ2)

Although the power of studies could be increased by increasing the sample

size at the subject level, it may generally be more efficient to increase the

reliability of measurements at the within-subject (replicates) level (i.e. take

repeated measurements on individual subjects). This raises the general

question of how best to allocate resources between the two levels so as to

maximise research efficiency: increase subject numbers or increase the

number of repeated measurements on each subject. Snijders and Bosker

(1993) and Mok (1995) address this issue, and Snijders, Bosker and

Guldemond offer free, downloadable software (PINT = ‘power in two-level

designs’ at http://stat.gamma.rug.nl/snijders/multilevel.htm. Thus, a

comprehensive discussion of the issue will not be presented here.

In summary, for the gastrocnemius medialis muscle, there was no significant

difference between mathematical and curvimeter measures of FL. The

291

mathematical method therefore provided a good estimation of fascicle

length in relaxed, contracted and relaxed-contracted conditions. Nonetheless,

there was a trend toward greater error in the mathematical method compared

to curvimeter measures (which were assumed to be accurate measures of FL)

in relaxed muscle where fascicles are long. This suggests that differences in

FL determined by the two methods would be greater for muscles with long

fascicles. The reliability of the mathematical method for measures of a single

muscle point was low. However, by taking the average of repeated measures

on subjects, reliability increased significantly. Thus researchers using

mathematical estimation of FL from muscle thickness and pennation

measurements should consider increasing the number of repeated measures

of individual subjects to improve reliability and increase statistical power.

292

Relaxed muscle Model A1 1 Model A2 2 Model A3 3

Fixed effects Coefficient S.E. Coefficient S.E. Coefficient S.E. β0ij = intercept 55.52 2.87 54.51 3.16 49.58 3.46 β1 = estFLr 0.11 0.04Random effects 10

u0j : Var(subjects) 48.73 28.41 53.39 34.57 38.21 22.20 e0ij : Var(replicates) 5.38 1.12 57.12 11.91 4.95 1.03Statistics-2LL 11 260.33 370.16 254.00ICC 12 0.90 0.48ρ2

13 0.99 0.89R1

2 14 0.20R2

2 15 0.21Contracted muscle Model B1 4 Model B2 5 Model B3 6

Fixed effects Coefficient S.E. Coefficient S.E. Coefficient S.E. β0ij = intercept 37.39 2.35 36.95 2.41 32.61 2.85 β1 = estFLc 0.13 0.05Random effects 10


13 0.99 0.93R1

2 14 0.22R2

2 15 0.23Relaxed - contracted Model C1 7 Model C2 8 Model C3 9

Fixed effects Coefficient S.E. Coefficient S.E. Coefficient S.E. β0ij = intercept 32.55 2.43 31.50 2.740 27.82 2.89 β1 = est∆FL 0.15 0.06Random effects 10


13 0.96 0.85R1

2 14 0.18R2

2 15 0.20mFL: measured fascicle length (digital curvimeter)estFL: estimated fascicle length (mathematical method)r: relaxed muscle, c: contracted muscle1 Model A1: dependent variable = mFLr; independent variable = intercept only2 Model A2: dependent variable = estFLr; independent variable = intercept only3 Model A3: dependent variable = mFLr; independent variables = intercept, estFLr4 Model B1: dependent variable = mFLc; independent variable = intercept only5 Model B2: dependent variable = estFLc; independent variable = intercept only6 Model B3: dependent variable = mFLc; independent variables = intercept, estFLc7 Model C1: dependent variable = m∆FL; independent variable = intercept only8 Model C2: dependent variable = est∆FL; independent variable = intercept only9 Model C3: dependent variable = m∆FL; independent variables = intercept, est∆FL10 Variance components and their standard errors (SE)11 –2LL = minus 2 loglikelihood = deviance12 ICC = intraclass correlation coefficient = ρ1 = reliability of a single replicate13 ρ2 = reliability of mean of 9 replicates as measure of a subject

293

14 R12 = proportion of replicate variance explained

15 R22 = proportion of subject variance explained

Table 1. Results of the multilevel regression analysis for relaxed (A), contracted (B) andrelaxed-contracted (C) conditions. Fascicle length calculated by curvimeter (1) andmathematical (2) methods are indicated in the ‘β0ij = intercept’ row and are in the units ofmillimetres. For all contraction states, mathematical estimates were slightly, but notsignificantly, lower than curvimeter estimates. Variance of measures at one site on themuscle were higher for mathematical estimates [e0ij : Var(replicates)], although variancecalculated on the mean of repeated measures (ie at the subject level) was relatively similarbetween the methods [u0j : Var(subjects)]. Reliability of fascicle length estimates at individualsites using the mathematical method were low (ICC = ρ1) although reliability was improvedsubstantially when repeated measures were averaged (ρ2). Models A3, B3 and C3 show theprediction of measured fascicle length (mFL; curvimeter estimates) from estimated fasciclelength (estFL; mathematical estimates) with proportions of replicate and subject varianceexplained (R1

2 and R22 respectively). There was no statistically significant difference between

measured fascicle lengths and those predicted from estimated fascicle length although theproportion of variance explained was low.

294

REFERENCES

Burkholder, T.J., Fingado, B., Baron, S., & Lieber, R.L. (1994). Relationship

between muscle fiber types and sizes and architectural properties in the

mouse hindlimb. Journal of Morphology, 221: 177-190.

Fukunaga, T., Ichinose, Y., Ito, M., Kawakami, Y., & Fukashiro, S. (1997).

Determination of fascicle length and pennation in a contracting human muscle

in vivo. Journal of Applied Physiology, 82(1): 354-358.

Goldstein, H. (1995). Multilevel Statistical Models. 2nd Edition London:

Edward Arnold.

Henriksson-Larsén , K., Wretling, M.-L., Lorentzon, R., & Öberg, L. (1992). Do

muscle fibre size and fibre angulation correlate in pennated human muscles?

European Journal of Applied Physiology, 64: 68-72.

Herbert, R.D. & Gandevia, S.C. (1995). Changes in pennation with joint angle

and muscle torque: in vivo measurements in human brachialis muscle.

Journal of Physiology, 484.2: 523-532.

Hox, J.J. (1994). Applied Multilevel Analysis. Amsterdam: TT-Publikaties.

Available in electronic form at www.ioe.ac.uk/multilevel/amaboek.pdf.

Kawakami, Y., Abe, T., & Fukunaga, T. (1993). Muscle-fiber pennation angles

are greater in hypertrophied than in normal muscles. Journal of Applied

Physiology, 74(6): 2740-2744.

Kawakami, Y., Abe, T., Kuno, S., & Fukunaga, T. (1995). Training-induced

changes in muscle architecture and specific tension. European Journal of

Applied Physiology, 72: 37-43.

Kawakami, Y., Ichinose, Y., & Fukunaga, T. (1998). Architectural and

295

functional features of human triceps surae muscles during contraction.

Journal of Applied Physiology, 85: 398-404.

Kawakami, Y., Ichinose, Y., Kubo, K., Ito, M., Imai, M., & Fukunaga, T. (2000).

Architecture of contracting human muscles and its functional significance.

Journal of Applied Biomechanics, 16: 88-98.

Kumagai, K., Abe, T., Brechue, W.F., Ryushi, T., Takano, S., & Mizuno, M.

(2000). Sprint performance is related to muscle fascicle length in male 100-m

sprinters. Journal of Applied Physiology, 88: 811-816.

Mok, M. (1995). Sample size requirements for 2-level designs in educational

research. Multilevel Modeling Newsletter, 7(2): 11-15.

Narici, M.V., Bonzoni, T., Hiltbrand, E., Fasel, J., Terrier, F., & Cerretelli, P.

(1996). In vivo human gastrocnemius architecture with changing joint angle at

rest and during graded isometric contraction. Journal of Physiology, 496.1:

287-297.

Snijders, T.A.B. & Bosker, R.J. (1993). Standard errors and sample sizes in

two-level research. Journal of Educational Statistics, 18, 3: 237-260.

Snijders, T.A.B. & Bosker, R.J. (1999). Multilevel Analysis: An Introduction to

Basic and Advanced Multilevel Modeling. London: Sage Publications Ltd.

Van Eijden, T.J.G.J., Korfage, J.A.M., & Brugman, P. (1997). Architecture of

the human jaw-closing and jaw-opening muscles. The Anatomical Record,

248: 464-474.

296

APPENDIX G

FORWARD HACK SQUAT DATA COLLECTION SCHEMATIC

297

1

2

3

4

6

5

7

8

9

10

11

13

12

14

15

1618

17

299

Diagram(ICAM)

Description/definition

Setpoint: implements voltage reference, DC voltage – (1) 10 V, (2)0 V.Analog output: directs data stream to an output on an analogmodule, here it powers the load cell (3) or position transducer (4).Analog input: receives external signals, e.g. fromtransducers/potentiometers. (5) received force input, amplifier gain= 300 volts/volt, DC offset range = 127. (6) received position input,amplifier gain = 10 000 volts/volt, DC offset range = 127.Zero order hold: set to hold value in input data stream [force (7)or position (8)] until next trigger (see below).Subtraction: subtracts two input values (e.g. a raw input from aheld [see above] value).Multiplication: multiplies two input values.

Variable amplifier: amplifies input data stream by a specifiedvalue using a potentiometer while the system is running. (9)calibrate force, gain = 0.742 units/unit, (10) calibrate position, gain= 1.02 units/unit.Display trace: displays a moving trace of the values of a datastream. (11) force trace, (12) position trace.Numeric display: displays a value in numeric form.

Peak detector: measures the peak value of a signal, can be resetto a specified level (usually zero) before each data acquisitionperiod (trial). (13) detects peak force, resets to zero.Square wave generator: provides a square wave at frequencyproportional to the voltage at its input, allows setting to 0 V (as inthis case) to provide 0 Hz. (14) oscillator calibration = 10 Hz/unit,frequency with 0V input = 3 Hz, Peak to peak amplitude = 10 units,zero offset.Check box or trigger: triggers an event such as data collection orreset. (15) collect data.Pulse generator: outputs pulse of specified duration. Used here tocollect 400 samples of force and position data over a 4 s timeperiod.Variable set point: implements a floating point variable voltagereference, allows reference voltage to be altered while program isrunning. (16) set to ‘angle = 51 deg’.Function: converts X to Y. (17) convert degrees to radians, (18)cos function to calculate vertical component of force.

Effect of Movement Pattern and Velocity of Strength Training

Documents

Transcript of Effect of Movement Pattern and Velocity of Strength Training