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 Measure with 1 RM – In rehab 1 Rm too difficult for weak or injured muscles Could use a 10 RM – weight not as stressful

Definitions Muscular Endurance Ability to perform repetitive muscular contractions against some resistance ( less than max load) Depends on energy systems As strength increases, endurance increases

Definitions Power Strength applied over a distance for a specific amount of time P=Fxd/T Ability to generate force quickly Combination of strength and speed Performance is limited without power Speed depends on coordination , efficiency of movement and timing Power is developed after strength ( in rehab)

Fiber Types Slow Twitch Fibers Fast 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 Muscle Fiber changes due to training Both fiber types exist in individual muscles Ratio varies by muscle and by individual Genetically determined Fiber changes due to training Enhanced metabolic capabilities through specific training Can fiber type change?

Muscle Strength and Muscle Endurance High intensity and low reps at one end of continuum – strength gains Low intensity and high reps at other end of continuum – muscle endurance gains Strength gains can be achieved with high rep and as can endurance gains with low reps but not as well – good to remember for rehab …. General rule a thumb Strength – 10 reps Endurance 15- 20 reps

Muscle Strength and Muscle Endurance Berger 1962 – sets – three sets beneficial for strength training This study has not been replicated ACSM- one set of 8- 12 reps to fatigue to increase strength Recovery times vary for type of exercise Isometric – 1 minute Isotonic – 30 sec to a minute Isokinetic – 2-4 minutes

Types of Contraction Isotonic contraction Dynamic involves a change in the muscle length Concentric contraction Muscle shortens Eccentric Contraction Muscle lengthens 20-40 % more force can be produced More likely hood of DOMS Isometric contraction Contraction that produces muscle tension but no change in muscle length

Types of Contraction Isokinetic Velocity is controlled ( speed is unchanged) where as the resistance is changed Often called accommodating resistance

Factors That Determine Levels of Strength, Endurance and Power Size of Muscle Proportional to cross-sectional diameter of muscle fibers Hypertrophy Increase in muscle size Atrophy Decrease in muscle size Can occur in as little as 48 hours Consistent exercise essential to prevent

Factors Continued Number of Muscle Fibers Strength is a function of the number and diameter of muscle fibers Number of fibers is inherited characteristic

Factors Continued Neuromuscular Efficiency Strength 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 rate Enhance synchronization of motor unit firing

Evaluating Muscle strength Isokinetic devices, cable tensiometers , isometric strength Manual Muscle test The basis of this test is assessment of the muscles ability to move a joint through a ROM Muscle strength is graded from 0-5 Always remember ACTIVE ROM first Resistance testing – isometric , mid range provide stabilization

Strength equipment Varies greatly due to availability and cost , size of room Manual resistance – resistance force applied by therapist or by patient Advantage – no equipment required, cost , hands on , immediate feedback , can easily modify resistance applied , can modify speed and can be easily incorporated in to a program Disadvantages- requires one on one work – time consuming , manual resistance nor measurable , not a consistent force Body weight – use of patient’s own weight Advantage- no equipment , performed anywhere , cost , functional activities , performed independently Disadvantage – no guarantee doing right when not supervised ,can not tolerate weight bearing ex

Strength equipment Rubber tubing /bands – dynamic resistance – lots of different weights Advantage – cost is low, ex at home , not bulky can be taken on road trips ,can make progressions , can mimic functional exercises Disadvantage – performed independently – unsure of technique, resistance greater at end when stretched , easier to use for upper than lower body Free weights – cuffs , bar bells Advantage – variety of free wts available, measurable changes ,can be used in functional activities Disadvantages – safety , training supervision using too much weight, boring

Strength equipment Isotonic machines – constant load during exercise Advantage- safety , readily available in gyms , multi station units , can work more unsupervised Disadvantage – weight restrictions due to muscle strength , boring , cost Isokinetic machines – accommodating resistance machines - biodex and cybex Advantage- constant speed and accommodating resistance , max and sub max outputs, patterns , measurable results ( computer charts graphs ) Disadvantage- cost $40,000, exercises are mostly OKC

Exercise Progression No Pain , during , after , next day ( DOMS) No inflammation Make attainable goals yet challenging Progressive overload – loads must increase progressively – overload principle Cross training – training contralateral side – can be used when limb movement is restricted

Strength Four principles SNAP Specific exercise No Pain Attainable goals Progressive overload

Physiological Adaptations Summary Improved neuromuscular efficiency Muscle hypertrophy Number of muscle fibers does not increase Increased size and number of myofilaments Actin and myosin Increased number of capillaries No 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/adaptation Increased metabolic enzymes Increased ability to withstand metobolic wastes

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

Open and Closed Kinetic Chain Open Kinetic Chain Distal segment ( hand or foot ) moves freely in space Movements in other segments within the chain are not predictable Kicking , throwing open kinetic chain Advantage – ex not delayed if can not weight bear Closed Kinetic Chain Distal segment is weight bearing Foot/hand meets resistance, movement of more proximal segment occurs in predictable pattern Running , handstands Less shear force with CKC- safer to use especially in early rehab program

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.