Stretching 3.pdf

ACUTE EFFECTS OF STATIC AND BALLISTIC

STRETCHING ON MEASURES OF STRENGTH

AND POWER

MICHELLE N. SAMUEL, WILLIAM R. HOLCOMB, MARK A. GUADAGNOLI, MACK D. RUBLEY,

AND HARVEY WALLMANN

Sports Injury Research Center, University of Nevada, Las Vegas, Nevada

ABSTRACT

Samuel, MN, Holcomb, WR, Guadagnoli, MA, Rubley, MD, and

Wallmann, H. Acute effects of static and ballistic stretching on

measures of strength and power. J Strength Cond Res 00:

1–7, 2008—Preactivity stretching is commonly performed by

athletes as part of their warm-up routine. However, the most

recent literature questions the effectiveness of preactivity

stretching. One limitation of this research is that the stretching

duration is not realistic for most athletes. Therefore, the purpose

of this study was to determine the effects of a practical duration

of acute static and ballistic stretching on vertical jump (VJ),

lower-extremity power, and quadriceps and hamstring torque.

Twenty-four subjects performed a 5-minute warm-up followed

by each of the following three conditions on separate days with

order counterbalanced: static stretching, ballistic stretching, or

no-stretch control condition. Vertical jump was determined with

the Vertec VJ system and was also calculated from the ground-

reaction forces collected from a Kistler force plate, which also

were used to calculate power. Torque output of the quadriceps

and hamstrings was measured through knee extension and

flexion on the Biodex System 3 Dynamometer at 60��s21. Data

normalized for body weight were analyzed using five separate,

3 (stretch condition) 3 2 (gender) analysis-of-variance pro-

cedures with repeated measures on the factor of stretch

condition. The gender 3 stretch interaction was not significant

for any of the four measures, suggesting that the stretching

conditions did not affect men and women differently. The results

of this study reveal that static and ballistic stretching did not

affect VJ, or torque output for the quadriceps and hamstrings.

Despite no adverse effect on VJ, stretching did cause a

decrease in lower-extremity power, which was surprising.

Because of the mixed results, strength coaches would be better

served to use dynamic stretching before activity; this has been

consistently supported by the literature.

KEY WORDS vertical jump, torque, flexibility, performance

INTRODUCTION

Stretching before physical activity has been a popularpractice performed by athletes for many years.Strength coaches commonly recommend preactivitystatic stretching for their athletes without knowing

how this will affect their sports performance. This recommen-dation has been based on the idea that stretching enhancesperformance (11,19,26,29), prevents injury (11,19,26,29), andincreases flexibility (3,7,13,15,19,22,25,29,30,36). Recent re-search has shown that there is not much scientific evidenceto support this practice. Many authors have reported thatstretching before physical activity is, in fact, detrimental tosports performance, especially when this performance requiresmaximal force production (1,7,10,15,17,20,21,22,24). The mostrecent literature suggests that preactivity stretching hindersathletic performance by temporarily reducing the amount offorce that a muscle can produce (1,10,15,17,18,21–24,27,36).Many authors have speculated that this stretch induced

decrease is caused by a reduction of musculotendinous(MTU) stiffness, which reduces the muscle’s ability to effec-tively generate force (15,22). It has been shown that a stiffMTU allows for greater force production by the contractilecomponent when compared with a compliant MTU (33).However, this research is not consistent with others and hasbeen challenged by findings that stretching does not affectsports performance. Church et al. (3) found that staticstretching did not affect vertical jump (VJ) but that it did,however, decrease MTU stiffness because the static stretch-ing routine caused a significant increase in hamstring flex-ibility. Unick et al. (31) investigated the acute effects of staticand ballistic stretching on VJ and found that neither stretch-ing routine affected performance. Burkett et al. (2) found thata static stretching routine did not cause any significantchanges to VJ when compared with the control condition.A review of the current literature shows that the results of

many studies conflict with others; some report that staticstretching diminishes VJ performance (5,18,32,37,38),

Address correspondence to Michelle N. Samuel, [email protected].

00(0)/1–7

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whereas others report that static stretching has no effect at allon VJ (2,3,14,24,31). It is clear that there is not enoughconsistent research to conclude the definite effects of stretch-ing on sports performance, and more research is warranted.Therefore, the purpose of this study was twofold: to inves-tigate the acute effects of a practical duration of static andballistic stretching of the quadriceps and hamstrings on VJ,lower-extremity power, and torque output of the quadricepsand hamstrings, and to compare the effects of stretchingbetween genders. Ballistic stretching was included because itmay be an effective alternative to static stretching. Lower-extremity power and torque were assessed because they areimportant in many sports, and VJ was included as a practicalskill requiring power.

METHODS

Experimental Approach to the Problem

A randomized, counterbalanced, mixed-model experimentaldesign was used to determine the effects of static and ballisticstretching on measures of strength and power. The threedependent variables were VJ height, power, and torque. Thisdesign was able to test whether preactivity static and ballisticstretching affect performance. This design also allowed theauthors to establish whether a difference exists regarding theeffects of stretching between men and women.

Subjects

Twenty-four healthy university students (12 men, 12 women;age = 22 6 2.8 years, height = 168 6 7.8 cm, body mass =75 6 18.2 kg) volunteered for the study. All subjects werescreened for previous injuries to the lower-extremity beforeparticipation. The university institutional review board gaveapproval for all procedures. Subjects were required to reportto a research laboratory to read and sign a medical ques-tionnaire and an informed consent. Subjects performed threedifferent stretching protocols with order counterbalanced onthree separate days, with 48 hours between testing. The threeprotocols included static stretching, ballistic stretching, anda no-stretch control condition.

Procedures

Subjects were required to attend an orientation session inwhich they were familiarized with the testing procedures.Three days after familiarization, subjects returned for testing.On each testing day, subjects performed a 5-minute warm-upon a treadmill at a self-selected speed ranging from 3.0 to3.5 mph. This was immediately followed by one of thethree stretching conditions. Subjects performed two differentlower-body stretches focusing on the quadriceps and ham-strings. Vertical jump and lower-extremity power weredetermined with a countermovement jump (CMJ) that wasperformed on a Kistler force plate (type 9281B, KistlerInstrument Corp., Amherst, NY) approximately 30 secondsafter stretching. Vertical jump was simultaneously measuredwith the Vertec VJ System (Sports Imports, Columbus, Ohio).

Torque was assessed for the quadriceps and hamstrings andwas tested on the Biodex System 3 Dynamometer (BiodexMedical Systems, Shirley, NY).

Stretching Protocols. Subjects performed three repetitions ofeach stretch, with each repetition lasting 30 seconds, whichwas timed by the examiner. The stretching techniques weredemonstrated to the subjects before the protocol to ensurethat they performed them properly throughout the experi-ment. The following static stretches were performed:unilateral standing quadriceps stretch and unilateral seatedhamstring stretch. To perform the unilateral standingquadriceps stretch, subjects stood on one leg with a posteriorpelvic tilt and with one hand against a wall for balance.Subjects grasped their foot to bring the knee into flexion as faras possible, keeping the knee perpendicular to the floor, untila strong stretch sensation was felt in the quadriceps (Figure 1).All subjects were able to perform this stretch so that a strongstretch sensation was felt. To perform the unilateral seatedhamstring stretch, subjects were instructed to sit on anexamining table with an anterior tilt of the pelvis, with theinvolved leg extended and the knee of the uninvolved legflexed in a figure-four position. Subjects then leaned forward,flexing the hip and reaching with their hand toward their toesuntil a strong stretch sensation was felt in the hamstrings(Figure 2).

Figure 1. Unilateral standing quadriceps stretch.

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Static and Ballistic Stretching


For ballistic stretching, subjects performed the samestretches as previously described. However, instead ofholding the stretch, subjects were instructed to get into thespecific stretch position until a strong stretch sensation wasfelt. Within 2 seconds of feeling a stretch sensation, subjectsbounced through themovement at the end of range of motionat a rate of one bounce per second for a total of 30 seconds.To perform the ballistic stretching, a metronome was set at60 bpm, and subjects bounced to the beat of the metronome.When stretching the quadriceps, subjects flexed the knee untila strong stretch sensation was felt, and then each subjectextended the knee to the point at which the stretch sensationwas no longer felt. Subjects flexed and extended the kneerhythmically to the metronome within the identified range.When stretching the hamstrings, subjects flexed at the hipwhile reaching toward their toes until a strong stretchsensation was felt, and then extended at the hip to the pointwhere the stretch sensation was no longer felt. Subjectsbounced forward with hip flexion and backward by hipextension rhythmically to the metronome within theidentified range.For the no-stretch control condition, subjects only

completed the warm-up by walking for 5 minutes on thetreadmill, and then subjects immediately began VJ testing.

Vertical Jump and Power Testing

Vertical jump height was assessed by the force plate and theVertec VJ system, and lower-extremity power was assessed onthe force plate. Subjects performed three CMJs on each dayfollowing their stretching condition. Subjects were instructedto stand on both feet on the force plate and lower their bodytoward the ground by moving into flexion at the knee, hip,and trunk while extending both shoulders (Figure 3). Whensubjects comfortably reached this point of flexion, they

instantly jumped up as high as possible while reaching for theVertec VJ system with their dominant hand (Figure 4).Subjects jumped up and hit the highest marker possible onthe Vertec. The VJ height was determined from the highestmoved marker. Ground-reaction forces (GRF) were re-corded for each jump with the force plate. The highest VJdetermined by the Vertec VJ system from each testing sessionwas recorded. The height of this jump was also calculatedusing the GRF recorded by the force plate through thefollowing method. The sum of all forces produced duringthe CMJ was calculated from time 1 to time 2, to determinethe take-off velocity through the following equation:

FDt ¼ mDv

In the equation, F is the sum of all forces, t is time, m ismass,and v is vertical velocity at take-off. Time 1 was identified asthe point after the jump was initiated and the point at whichGRFequaled body weight. Time 2 was identified as the pointat which GRF decreased to equal body weight just beforetake-off. Take-off was identified as the point at whichGRF fellto zero. Take-off velocity was used to determine the VJ heightthrough the following equation:

mgh¼ 1=2 mv2

Figure 2. Unilateral seated hamstrings stretch.

Figure 3. Countermovement jump on force plate.


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In the equation, g is acceleration attributable to gravity, andh is VJ height. Power produced during this jump wasdetermined by calculating work, which is the product of thesum of all forces and vertical velocity at take-off (Fv).

Torque Output Testing. Each subject was positioned in theBiodex chair so that the axis of rotation of the dynamometerlined upwith the joint line of the right knee. The lower legwasstrapped to the dynamometer lever arm approximately twofinger-widths above the medial malleolus. To ensure reliablemeasurements, the dynamometer was calibrated, all stabili-zation straps were used to prevent unwanted movement,subject’s hands were required to remain free, and no visualfeedback was provided during testing. Subjects performedthree maximal isokinetic concentric muscle actions for kneeextension and flexion at 60��s21 through a 10–105� range ofmovement (0� = full knee extension) (Figure 5). The highestpeak torque from the three maximal repetitions was recordedfor each muscle and was used in the analysis.

Statistical Analyses

For each dependent measure, the largest recorded value fromthe three repetitions was used for the analysis. For example,the largest peak torque produced by the quadriceps andhamstrings under each condition was used for analysis. Datanormalized for body weight were analyzed using fiveseparate, 3 (stretch condition) 3 2 (gender) analysis-of-

variance procedures with repeated measures on the factor ofstretch condition. An alpha level of p # 0.05 was used as thelevel of significance.

RESULTS

The statistical analyses yielded very similar results acrossmeasures. These measures and their respective results aredetailed below.VJ–calculated: The main effect for stretch condition on VJ

as measured by the force plate was not significant, F1,22 =0.660, p = 0.425. The main effect for gender was significant,F1,22 = 67.645, p , 0.001. The gender 3 stretch interactionwas not significant, F = 0.023, p = 0.881.VJ–Vertec: The main effect for stretch condition on VJ as

measured by the Vertec VJ system was not significant, F1,22 =1.201, p = 0.285. The main effect for gender was significant,F1,22 = 68.168, p , 0.001. The gender 3 stretch interactionwas not significant, F = 0.030, p = 0.864 (Figure 6).Quadriceps torque: The main effect for stretch condition on

quadriceps torque was not significant, F1,22 = 0.427, p = 0.520.The main effect for gender was significant, F1,22 = 26.230, p,0.001. The gender 3 stretch interaction was not significant,F = 0.050, p = 0.825 (Figure 7).Hamstring torque: The main effect for stretch condition on

hamstring torque was not significant, F1,22 = 0.275, p = 0.605.The main effect for gender was significant, F1,22 = 6.692, p =0.017. The gender 3 stretch interaction was not significant,F = 0.008, p = 0.931 (Figure 6).These results suggest that static and ballistic stretching did

not affect VJ, hamstring torque, or quadriceps torque. Thegender3 stretch interaction was not significant for any of thefour measures above, suggesting that the stretching con-ditions did not affect men and women differently. However,the significant main effect for gender, even when the variable

Figure 4. Vertec vertical jump system.

Figure 5. Biodex System 3 Dynamometer at 60��s21.




was normalized for body weight, demonstrates that menproduced more torque and VJ than women.Power: The main effect for stretch condition on power was

significant, F1,22 = 7.124, p = 0.014. The main effect for genderwas significant, F1,22 = 76.260, p , 0.001. Once again, thegender 3 stretch interaction was not significant, F = 0.779,p = 0.387. These results indicate that the mean value for thecontrol group was significantly greater than the twostretching conditions. Normalized means for power were48.4, 48.9, and 50.1 for static, ballistic, and control,respectively (Figure 8). These results show that static andballistic stretching had an adverse effect on power. Thesignificant main effect for gender, even when the variable wasnormalized for body weight, demonstrates that men pro-duced more power than women.

DISCUSSION

The purpose of this study was to determine whether acutestatic and ballistic stretching had any effect on measures ofstrength and power, and to compare the effects of stretchingbetween genders. Static and ballistic stretching did not cause

any changes to three out of the fourmeasures when comparedwith the control condition. Vertical jump, quadriceps torque,and hamstring torque values were no different with the threestretch conditions. Vertical jump was assessed with twodifferent measures, a force plate and the Vertec VJ System.A correlation of 0.99 was found between these two measures,so the results will be discussed as one. The time lapse betweenstretching and performance would likely affect performance;therefore, it should be reported. The time from the end ofstretching until the assessment of VJ and power wasapproximately 30 seconds. The assessment of torque requireda more time-consuming setup, so the elapsed time wasapproximately 1 minute. However, the elapsed time was thesame for each stretch condition; thus, it did not affect ourcomparison of the three types of stretching.A number of studies have reported that static stretching had

a detrimental effect on VJ (5,32,37,38) and torque output(1,7,10,15,20,21,22,24). The exact mechanism for the stretch-induced decline in performance is not known; however,authors have speculated that a decrease in muscle activationand MTU stiffness are the cause (1,5,10,15,18,22,23,33).Power et al. (24) found that static stretching of the plantarflexors, hamstrings, and quadriceps for 4.5 minutes eachresulted in a 5.4% decrease in muscle activation; however, theauthors were not able to determine how long this decreaselasted. Studies that found muscle activation and MTUstiffness to decline for prolonged periods involved intensestretching that is not comparable with sports stretchingbecause of their excessive length and concentration (1,10).The results of this study conflict with these studies that foundstretching to cause decrements in VJ and torque.One reason for this discrepancymay be the difference in the

design of the present study when compared with others. Thepresent study was designed to test a practically relevantstretch duration similar to the routine used by athletes. This isthe reason that subjects only stretched each muscle for90 seconds total, in one set of three repetitions, each held for30 seconds. Most athletes do not spend prolonged periods oftime stretching before activity. The previous mentionedstudies (1,7,10,15,20,21,22,24) all used study designs that

Figure 7. Quadriceps and hamstring torque values for each stretchcondition.

Figure 6. Vertical jump height for each stretch condition. Figure 8. Power values for each stretch condition.



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required the muscle to be stretched for extended periodsranging from 8 to 30 minutes. Also, several of these studiesonly focused on one muscle; for example, Cramer et al. (6)had subjects perform four different static stretches, allfocusing on the quadriceps; each stretch was held for 30seconds each and was repeated four times. This stretchingroutine resulted in a total of 8 minutes spent stretching onemuscle. The present study focused on two muscles, thequadriceps and the hamstrings, which were chosen becausethey could both be tested for torque output and because bothfunction as major muscles used in the VJ. The difference in8 minutes devoted to a single muscle vs. 3 minutes devoted totwo muscles could certainly account for the differing results.The results that static and ballistic stretching did not affect

VJ or quadriceps and hamstring torque support the findings ofother studies (2,3,14,24,31). Burkett et al. (2) found thata static stretching routine of the lower body, consisting of 14stretches, each held for 20 seconds, did not cause anydetrimental effects to VJ. Unick et al. (31) found that staticand ballistic stretching of the lower body for 3 minutes didnot decrease VJ. The results of these studies and the presentstudy indicate that a practical stretch duration of 90 seconds,similar to the stretch duration used by athletes, can be usedpreactivity without adversely affecting VJ and torque output.Wallmann et al. (32) have suggested that the present VJ

results might be attributable to the specific muscles that arestretched. The present study used the same stretchingduration, 1.5 minutes, as the Wallmann et al. study (32), but itdid not stretch the same muscles. In the Wallmann et al.study, subjects only stretched the gastrocnemius after restingfor 15 minutes after prestretch measurements, and thesubjects’ VJ was significantly reduced after static stretching.Similar to the present study, Church et al. (3) used staticstretching of the quadriceps and hamstrings, and it wasdetermined that VJ was not affected by the static stretchingroutine. Further research should be completed to comparethe effects of acute static stretching on different musclegroups in regards to VJ.One measure that was significantly affected by stretching

was power. The results of the present study show that bothstatic and ballistic stretching caused significant declines inpower production when compared with the control condi-tion that involved no stretching. Power was calculated withthe GRFs that were collected from the force plate whilesubjects performed the VJ test. Vertical jump is commonlyaccepted as a predictor of power because VJ is related to legpower, which means that to perform a VJ, a person needs toeffectively generate force with his or her legs at a rapid speed.Surprisingly, the VJ test was not affected by the stretchingroutine as power was.It was hypothesized that static and ballistic stretching

would affect VJ and power equally. This, however, was not thecase in the present study. One potential explanation for this isthat the VJ requires a certain amount of technique. Therefore,the VJ used in this study comprised three factors: force, speed,

and technique. It is speculated that stretching does not haveany effect on VJ technique. In comparison, raw powerinvolves only force and speed. Therefore, the main differencein VJ and power is thought to be technique, and it is proposedthat the stretching routine did not affect VJ because of thetechnique involved with the actual movement. For example,a person could adequately produce enough power to jump 30in, but if the person’s technique were poor, he or she wouldnot effectively utilize the power to maximize jump height. Inthe present study, power was significantly reduced, but it didnot cause any changes to VJ. It should be mentioned that thedecrements, although significant, were relatively small. Staticstretching only caused a 3.4% decline, and ballistic stretchingonly caused a 2.4% decline. Power et al. (24) also foundsurprising results when subjects performed a static stretchingroutine that lasted 4.5 minutes per muscle. The results showthat the static stretching routine adversely affected torqueoutput and muscle activation of the quadriceps but did not,however, affect VJ. Power et al. (24) conclude that the VJ wasnot affected because it was performed unilaterally and thatthese types of jumps possibly benefit from compliant MTU.Although this finding was unexpected, another recent

study found a similar result with a different type of preactivitywarm-up. Cormie et al. (4) tested the effect of whole-bodyvibration on several performance variables and found thatvibration caused a significant increase in VJ yet no change inpeak power. Unfortunately, the authors offer no explanationfor these findings.Another significant finding from the study was the main

effect for gender. These results show that even when all valueswere normalized for body weight, men produced significantlyhigher results than did women for all four variables. Unicket al. (31) conducted a study using only women andsuggested that further research was needed to determinewhether stretching affects the genders differently. Throughthe design of the present study, it was possible to assess this.Despite the obvious performance differences betweengenders, it was determined that the static and ballisticstretching routine did not affect the genders differently. Theperformance of men was consistently and significantly higherthan the performance of women for all three stretchingconditions.

PRACTICAL APPLICATIONS

Results of the present study reveal that acute preactivitystretching does not affect genders differently when a practicalstretch duration of 90 seconds is used. The results also revealthat acute static and ballistic stretching performed preactivitydoes not affect VJ and torque output of the quadriceps andhamstrings. Coaches that use stretching as a part of the warm-up can continue to do so by limiting the duration of stretchingto 1.5 minutes per muscle. However, because power wasadversely affected, sports that require maximal power outputshould not be preceded with acute stretching. Instead, it issuggested that athletes perform a whole-body continuous




activity followed by dynamic stretching that involves re-hearsal of sport-specific movements. Dynamic stretching canfunction to properly prepare the athlete’s body for dynamicmovements without the stretch-induced decrements thathave been seen with preactivity static and ballistic stretchingby improving performance (8,9,17,35). If static stretching isused as a part of a training program, it should be performed atthe end of activity to increase range of motion (7,15,24) andto improve performance (12,23,28,34).

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