MUSCULAR STRENGTH, ENDURANCE AND POWER

Returning the athlete to competitive and functional

level following injury

Definitions

Muscular Strength Ability to generate force against some resistance Important to maintain normal levels of strength for

normal healthy living

Muscular Endurance Ability to perform repetitive muscular contractions

against some resistance As strength increases, endurance increases

Definitions

PowerAbility to generate force quickly Combination of strength and speed

Performance is limited without power

Types of Contraction

Isometric contraction Contraction that produces muscle tension but no

change in muscle length

Concentric contraction Contraction that causes muscle shortening while

tension increases to overcome some resistance

Eccentric Contraction Resistance is greater than the muscular force

being produced and muscle lengthens while producing tension

Types of Contraction

So what?Strength training must focus on

functioning of muscleMulti-planarVarious contractions - functionally

Factors That Determine Levels of Strength, Endurance and Power

Size of MuscleProportional to cross-sectional diameter of

muscle fibers

Hypertrophy Increase in muscle size

AtrophyDecrease in muscle sizeCan occur in as little as 48 hoursConsistent exercise essential to prevent

Factors Continued

Number of Muscle FibersStrength is a function of the number and

diameter of muscle fibersNumber of fibers is inherited characteristic

Factors Continued

Neuromuscular EfficiencyStrength is directly related to efficiency of

the neuromuscular system

Initial increases in strength during first 8-10 weeks are attributed to neuromuscular efficiency

Enhanced strength in 3 ways Increase motor unit recruitment Increase in firing rateEnhance synchronization of motor unit firing

Fiber Types

Slow Twitch Fibers

Type I or slow oxidative Resistant to fatigue Primarily associated with long duration, aerobic

type activities and postural muscles

Fast Twitch Fibers Type IIa (fast oxidative glycolytic) IIb (fast

glycolytic) Produce quick, forceful contractions by tendency

to fatigue

Fiber Types Cont’d

Ratio in MuscleBoth fiber types exist in individual musclesRatio varies by muscle and by individualGenetically determined

Fiber changes due to trainingEnhanced metabolic capabilities through

specific trainingCan fiber type change?

So What?

First 8-10 weeks is training to be efficientTechniqueNeurophysiological input

Position of loadPosition of limbTarget fiber type as well as contraction

type

Physiological Adaptations Summary

Improved neuromuscular efficiencyMuscle hypertrophy

Number of muscle fibers does not increase

Increased size and number of myofilaments Actin and myosin

Increased number of capillariesNo new capillaries Increase in dormant capillary activity to meet

needs of muscle

Strength of non-contractile structures Tendons and ligament increase Increased bone-mineral content

Improved oxygen uptake If resistance training is high enough to elicit

a cardiovascular response/adaptationIncreased metabolic enzymes Increased ability to withstand metobolic

wastes

Overload

To improve strength, muscle must be worked at a level higher than it is accustomed to

Without overload, muscle will maintain strength as long as training is continued against a resistance that it is accustomed toExistence of current strength but no

additional strength gain

Overload Cont’d (Prentice, 2004)

In rehabilitation, progressive overload is limited to a degree by the healing process

Rate of progression determined by injured athlete’s response to specific exercise Increased pain and/or swelling indicate

overload too high

Overtraining

Imbalance between exercise and recovery Training exceeds physiological and psychological

capacity of individual

Can have negative effect on strength training May result in psychological or physiological

breakdown Injury, illness, and fatigue can be indicators

Progressive Resistive Exercise Techniques and Programs

TerminologyRepetitionsRepetition

maximum (RM)Set IntensityRecovery periodFrequency

Multiple potential routinesSingle setTri-setsMultiple sets SupersetPyramidSplit routineCircuit Training

Progressive Resistive Exercise Techniques and Programs Cont’d

Must consider 4 areasAmount of weight to be usedNumber of repetitionsNumber of setsFrequency of training

Open and Closed Kinetic Chain

Open Kinetic Chain Movements in other segments within the chain are not

predictable Origin is fixed and contraction causes movement of the

insertion

Closed Kinetic Chain Foot/hand meets resistance, movement of more proximal

segment occurs in predictable pattern Not necessarily weight bearing Insertion fixed and contraction causes movement in of

origin Concurrent shift: two joint muscles must work

concentrically and eccentrically at the same time

Open Kinetic Chain )

Characteristics Increased acceleration forces Decreased resistance forces Increased distraction and rotational forces Usually isolated to a single joint Increased deformation of joint and muscle

mechanoreceptors Concentric acceleration and eccentric

deceleration Promotion of functional activity

Open Kinetic Chain )

Advantages Isolation of exercise to a specific joint Isolation of specific muscle groupsUsually single planeAllow deficits to specific structures t be

addressed when athlete unable to weight bear or when closed kinetic chain would cause compensation

Closed Kinetic Chain (

Characteristics Increased joint compression Increased joint congruency, hence stabilityDecreased shear with muscle contractionDecreased accelerationLarge resistance forcesStimulation of proprioceptorsEnhanced dynamic stability

Closed Kinetic Chain )

AdvantagesSafer than open kinetic chainLess stress on healing structuresMore functional for lower extremity

activities, except kicking

Progressive Resistive Exercise Techniques and Programs Cont’d

Regardless of program…. Initially exercises are performed daily

WHY?

Weight, sets, repetitions, rest governed by injured person’s response to exercise

When pain and swelling resolved, exercise intensity can increase

Exercise consistently every other day 3-4x/week What phase of healing?

Girth Measurments

Often girth measurements are taken prior to the development of the rehab program to provide the therapist with a starting point.

Measurements are repeated a intervals on the program to be used as a way to monitor progress

Increases and decreases in girth size are thought to be related to muscle strength

Girth measurements

To ensure accurate and reliable measurements the therapist should use the same anatomical landmarks when performing the measurements.

Contracted / relaxed ??Assignment # 3