Muscular Strength and Endurance

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Muscular Strength and EnduranceMuscles make up more than 40% of your body massWell-developed muscles can assist with:

Daily routinesProtection from injuryEnhancement of your overall well-being

Muscular strength is the amount of force a muscle can produce with a single maximum effort Muscular endurance is the ability to resist fatigue while holding or repeating a muscular contraction

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Basic Muscle PhysiologyMuscles consist of individual muscle fibers (cells) connected in bundles Muscle fibers are made up of smaller protein structures called myofibrilsMyofibrils are comprised of contractile units called sarcomeres (actin and myosin)Proper strength training causes individual fibers to increase the number of myofibrils resulting in hypertrophy Inactivity can reverse this process resulting in atrophy

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Skeletal Muscle Tissue

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SarcomereGives muscle its striated appearance.– Lighter area: I band– Darker area: A band

Smallest contractile unit in the body.– ~ 4.0 μm at rest– ~ 2.5 μm when contracted

Actin– Thin filament

Myosin– Thick filament

TroponinTropomyosin

SarcomereA band – Total length of the myosinH zone – Only myosinM line – Center of the sarcomereI band – Only actinZ lines – Ends of the sarcomere

Actin-Myosin OrientationActin is the “sliding” filament.Myosin heads can attach to the actin binding sites to create a crossbridge.Myosin heads can pivot at the cost of ATP.

Muscle ContractionThe Sliding Filament Theory

Step 1: Nerve signal arrives at the myofibril and releases neurotransmitter ACh.Step 2: ACH depolarizes the sarcolemmaStep 3: Sarcolemma releases Ca2+

Step 4: Ca2+ binds to tropomyosin and “pulls” it off of the actin binding site.Step 5: Myosin head binds with actin forming corssbridge.

Muscle ContractionThe Sliding Filament Theory

Step 6: ATP binds to the crossbridge causing the myosin heads to pivot and the actin filaments to slide towards the M line.Step 7: Crossbridge activation continues as long as Ca2+ remains high.Step 8: Muscle stimulation stops and Ca2+ moves back into sarcolemma.Step 9: Calcium removal allows tropomyosin to return to its resting position, covering the actin binding site.

Basic Muscle PhysiologyHypertrophy is the development of large muscle fibers

Atrophy is the reduction of the size of the muscle fiber due to inactivity or injury

Hyperplasia is the increase in the number of muscle fibers. It is not thought that hyperplasia plays a significant role in muscle size in humans.

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Basic Muscle PhysiologySlow-twitch fibers are:

Fatigue resistantDon’t contract as rapidly and forcefully as fast-twitch fibersRely primarily on the aerobic energy system

Fast-twitch fibers: Contract rapidly and forcefully Fatigue more quickly than slow-twitch fibersRely more on the anaerobic energy system

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Muscle Fiber Types

Muscle Fiber TypesCharacteristic Type 2B Type 2A Type 1

Color White Pink Red

Fiber Diameter Large Intermediate Small

Capillary Density Low Intermediate High

Mitochondrial Density

Low Intermediate High

Glycolytic Capacity

High High Low

Oxidative Capacity

Low Medium/high High

Speed of Action Fast Fast Slow

Fatigue Resistance

Low Moderate/high High

Force Capacity High Intermediate Low

Motor UnitsA motor unit is made up of a nerve connected to a number of muscle fibers– Small motor units contain slow-twitch fibers while large

motor units contain fast-twitch fibers

Motor unit recruitment happens when strength is required; nerves assist with the action– The number and type of motor units recruited are

dependent upon the amount of strength required

Muscle learning is the ability to improve the body’s ability to recruit motor units

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Strength Gains

Neural factors:– Adaptive alterations in nervous system

function that elevate motor neuron output largely account for the rapid and large strength increases early in training.

Muscular factors:– An increase in muscular tension with

exercise training provides the primary stimulus to initiate the relatively slow process of hypertrophy.

Contributions to Strength Improvements

Training Duration (weeks)

Neural Factors Muscular Hypertrophy

2 90% 10%

4 60% 40%

6 20% 80%

8 10% 90%

Types of Muscle Actions

Benefits of Muscular Strength and Endurance

Improved performance of physical activities

Injury prevention

Improved body composition

Enhanced self-image and quality of life

Improved muscle and bone health with aging

Metabolic and heart health

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Assessing Muscular Strength and Endurance

Muscular strength is usually assessed by measuring the maximum amount of weight a person can lift one time (1 RM)– Also can use an estimated maximum test (submaximal

lift)– Need to train for several weeks before testing– Retest after 6-12 weeks

Muscular endurance is assessed by counting the maximum number of repetitions of a muscular contraction a person can perform to fatigue

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1RM

One-repetition maximum refers to the maximum amount of weight lifted one time using proper form during a standard weight-lifting exercise. – Not always practical– Can be difficult to attain

Estimating 1RM1RM (kg) = 1.172 X 7-10RM (kg) + 7.704

Effects of Specific Repetition Ranges

Goal Reps

Power 1 - 6

Hypertrophy 6 -12

Strength 8 - 12

Endurance 10 - 25

Power RecommendationsLoading > 80% 1RM

Reps 1 - 6

Sets 3 - 6

Rest 1 – 2 min

Velocity Fast

Frequency 2 - 4 X/week

Hypertrophy Recommendations

Loading 70-90% 1RM

Reps 6 - 12

Sets 1 - 3

Rest 2 - 3min

Velocity Slow/moderate

Frequency 4 - 6 X/week

Strength Recommendations

Loading 70 - 80% 1RM

Reps 8 - 12

Sets Multiple

Rest 1 – 2 min

Velocity Slow

Frequency 2 – 6 X/week

Endurance Recommendations

Loading 50 - 70% 1RM

Reps 10 - 25

Sets Multiple

Rest < 1 min

Velocity Moderate

Frequency 4 – 6 X/week

Creating a Successful Strength Training Program

Static (isometric) exercise involves a muscle contraction without a change in the length of the muscle or joint angle

An example is pushing against a brick wallConsidered useful in strength building after an injury/surgeryIsometric contractions are usually held for 6 seconds

Dynamic (isotonic) exercise involves a muscle contraction with a change in the length of the muscle

Two typesConcentric contractionEccentric contraction

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Static vs. Dynamic Strength Training

Comparing Static and Dynamic Exercises

Static exercises: Isometric exerciseMuscle contraction without a change in the length of the muscle or the angle in the jointRequire no equipmentBuild strength rapidlyUseful for rehabilitation

Dynamic exercises: Isotonic exerciseMuscle contraction with a change in the length of the muscleCan be performed without or with equipmentCan be used to develop strength or enduranceUse full range of motionAre more popular with the general population

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Training Methods

Other Dynamic Methods– Constant and variable resistance– Eccentric loading– Plyometrics– Speed loading – Kettlebells– Isokinetic

Other Training Methods and Types of Equipment– Resistance Bands - Medicine balls– Exercise (stability) balls - Suspension training– Pilates - Stones– No-equipment calisthenics

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Applying the FITT PrincipleFrequency: At least 2-3 nonconsecutive days/week allowing 1 day of rest between workouts– Based on the ACSM guidelines

Intensity: (Amount of Resistance) Strength requires lifting 70- 80% of your 1 RM; Endurance requires 50-70% of your 1 RM

Time: (Repetitions and Sets) 8-12 reps for strength; 10-25 reps for endurance; making sure each set leads to overload of that muscle group

Type: (Mode of Exercise) target large muscle groups (8-10 exercises) including opposing muscles– Agonist muscle groups – Antagonist muscle groups

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Warm Up and Cool DownEveryone should perform a warm-up prior to each weight training session

A general warm-up (like walking or easy jogging) and performing light reps of each exercise is recommended before every training session

To cool down after weight training, relax for 5-10 minutes by stretching—which could possibly prevent soreness

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Getting Started and Making Progress

First few sessions – Should be devoted to learning the movements– Choose a weight you can move easily 8-12 times; 1 set and

rest 1-2 minutes between exercise– Goal is to be doing 1-3 sets of 8-12 repetitions

Progress– “Two-for-two” rule– General guideline for increasing weight – increase by

approximately 5% of what you are currently lifting– Your rate of improvement depends on how hard you work and

your bodies response to resistance training

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Weight Training SafetyUse proper lifting techniques– ACSM recommends a moderate rate for

each repetition– Strive to maintain a neutral spine position

during each exercise

Use spotters with free weightsBe alert for injuries– R.I.C.E. principle

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A Caution About Supplements and Drugs

Supplement manufacturers often make claims that their products will promote or enhance sport performance or physique

Most of these substances are ineffective and expensive as well as possibly dangerous

Before purchasing and using these products, find other resources that document these dietary aids

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