Muscular Function Assessment

1. Muscular Function Assessment Gallagher - OEH ch 21(CCW)

2. Outline • Muscle strength is a complex function that can vary with the methods of assessment • Definitions and introduction • Assessment methods • Variables impacting performance

3. Muscle Function • Gallagher • Strength - capacity to produce a force or torque with a voluntary muscle contraction • Power - Force * distance * time-1 • Endurance -ability to sustain low force requirements over extended period of time • Measurement of human strength • Cannot be measured directly • interface between subject and device influences measurement • Fig 21.1 Biomechanical eg. • Q = (F * a)/b or c or d • force from muscle is always the same • results are specific to circumstances • dynamic strength - motion around joint • variable speed - difficult to compare • static or isometric strength- no motion • easy to quantify and compare • not representative of dynamic activity

4. Factors Affecting Strength • Gender • Age • Anthropometry • Psychological factors - motivation • table 21.1 • Task influence • Posture • fig 21.2 angle and force production • Duration • Fig 21.3 • Velocity of Contraction • Fig 21.4 • Muscle Fatigue • Static vs dynamic contractions • Frequency and work / rest ratio • Temperature and Humidity • inc from 20-27 C - decrease of 10-20% in muscle capacity

5. Strength Testing (intro) • Isometric strength testing • standardized procedures • 4-6 sec contraction, 30-120 sec rest • standardized instruction • postures, body supports, restraint systems, and environmental factors • worldwide acceptance and adoption • Dynamic strength • isoinertial (isotonic)- mass properties of an object are held constant • Psychophysical - subject estimate of (submax) load - under set conditions • isokinetic strength • through ROM at constant velocity • Uniform position on F / V curve • Standardized • Isolated muscle groups

6. Strength testing • Testing for worker selection and placement • Used to ensure that worker can tolerate physical aspects of job • similar rates of overexertion injuries for stronger and weaker workers • Key principles • Strength test employed must be directly related to work requirements • must be tied to biomechanical analysis • Isometric analysis fig 21.5 • for each task - posture of torso and extremities is documented (video) • recreate postures using software • values compared to pop. norms • industrial workers • estimate % capable of level of exertion • predict stress on lumbar spine

7. Isometric Considerations • Discomfort and fatigue in isometrics thought to result from ischemia • Increasing force, increases intramuscular pressure which approaches then exceeds perfusion pressure - lowering then stopping blood flow • Partial occlusion at 20-25% MVC • Complete occlusion above 50% MVC • Fig 15-19 Astrand • Max hold time affected by % MVC • Recommend less than 15% for long term requirements • Fig 15-20 Astrand • With repeated isometric contractions Force and Frequency influence endurance • Optimal work / rest ratio of 1/2 • Duration important as well (Astrand - blood flow)

8. Isoinertial Testing • Consider - biomechanics and grip • Stabilization requirements • justification of cut off scores • Examples from industry • SAT - strength aptitude testing • air force standard testing • Pre-selected mass - increase to criterion level - success or failure • found incremental weight lifted to 1.83m to be best test as well as safe and reliable • PILE - progressive inertial lifting evaluation • lumbar and cervical lifts -progressive weight - 4 lifts / 20 seconds • standards normalized for age, gender and body weight • variable termination criteria • voluntary, 85 % max HR, 55-60% body weight

9. Psychophysical testing • psychophysical methods • workers adjust demand to acceptable levels for specified conditions • provides ‘submax’ endurance estimate • Procedure - • subject manipulate one variable-weight • Either test : starting heavy or light • add / remove weight to fair workload • Fair defined as : without straining, becoming over tired, weakened, over heated or out of breath • Study must use large number’s of subjects • evaluate / design jobs within determined capacities by workers • 75% of workers should rate as acceptable • If demand is over this acceptance level; 3 times the injury rate observed to occur

10. Psychophysical (cont) • Summary • Table 21.2 (Snook and Cirello) • Advantages • realistic simulation of industrial tasks • very reproducible - related to incidence of low back injury • Disadvantages • results can exceed “safe” as determined through other methodology • biomechanical, physiological

11. Isokinetic Testing • Isokinetic testing • Evaluates muscular strength throughout a range of motion at a constant velocity • Consider - velocity, biomechanics • However; • humans do not move at constant velocity • isokinetic tests usually isolated joint movements • may not be reflective of performance ability • Redesign of isokinetic testing • multi joint simulation tasks for industry • fig 21.8 • Better, as they require core stabilization • still in development, therefore limited validity

12. Outline • Aging introduction • Aging process • Physiological capacity and aging • CV and skeletal muscle only • Exercise Prescription

13. Exercise and Aging Skeletal Muscle • Brooks - Ch 32 • Brooks - Ch 19 (p444-451)

14. Decline of physiological capacity is inevitable consequence of aging • physical inactivity may contribute to these declines • complicating the quantification of the effects of aging • Body composition with aging • inc % body fat / dec lean body mass • studies illustrate selective decline in sk ms protein vs non muscle protein • body K+ and Nitrogen levels • muscle peaks at 25-30 yrs • decline in X sec area, ms density • inc intra-muscular fat • Resting Metabolic Rate (RMR) • decline associated with dec ms mass

15. Life expectancy, Span, and Morbidity • Lifestyle (diet, exercise) will influence performance and health with aging, but will not halt the aging process. • Life expectancy has changed dramatically in this century • 1900: 47 years ; 2000: 76 years • Maximum lifespan (100 years) has not • Quality of life, wellness, is important • North Americans only have healthy quality life during 85% of their lifespan, on average • Good lifestyle choices can compress morbidity - state in which they can no care for themselves • Reducing morbidity from 5-10 years to 1 or 2 can add quality years to your life • Table 32-1

16. Aging and Exercise • Lifestyle choices (deconditioning) • Some people physically deteriorate with age due to a lack of exercise, obesity, poor diet, smoking, and stress. • Other individuals are active and are still fit in their 50s, 60s and 70s. • Disease and physiological function • Disease further complicates our understanding of the aging process. • osteoarthritis, atherosclerosis • Sedentary death syndrome (SeDS) • Clear that adaptation to exercise has a genetic basis (plasticity) • Effort to find molecular proof that physical inactivity is an actual cause of chronic disease • Some researches want to move away from using sedentary individuals as controls in experiments - eg GLUT 4 • Physiological systems vary in the extent to which they deteriorate

17. The Aging Process • Aging involves diminished capacity to regulate internal environment • Body structures are less capable and less resilient • Reduced capacity is evident in; • Reaction time, resistance to disease, work capacity, and recovery time • Table 32-2 (good summary) • Reduced capacity of many systems • Genetics has an important influence on length of life; genetics in concert with environmental factors affects the quality of that life • Aging may be related to; • accumulated injury, autoimmune reaction, problems with cell division, • abnormalities of genetic function (free radicals, radiation, toxins), • wear and tear

18. Dietary Restriction and Aging • Dietary restriction extended mean lifespan in rats by 30-50 % • Similar results in monkeys • Several possible explanations : • Retardation of basic metabolism and biological processes of aging • Suppression of age-related pathologies - • found to impact immune system, protein turnover, bone loss, neural degeneration • Reduction of oxidative stress by ROS through increased antioxidant activity

19. Physiological Capacity • Physiological functioning peaks ~ age 30 • Table 32-3 • ~.75 to 1 % decline per year after 30 • Declines in VO2 max, Q max, strength ,power, and neural function; also increases in body fat • All positively impacted by training • Maximal O2 consumption and age • VO2 max declines ~30% (age 20-65) • Fig 32-2 - (training and age vs VO2 max) • Significant individual variability • Similar declines with age in trained and untrained - trained has higher capacity • Due to decrease in max HR, SV, Power, fat free mass and A-V O2 difference • Heart Rate and age • Sub max - HR lower at relative intensity but higher at same absolute intensity • Cardiovascular drift is higher with age • Longer recovery time • Dec b- adrenergic responsiveness (dec HR max)

20. Stroke Volume and Cardiac Output (Q) • Aging  the hearts capacity to pump blood • Q and SV are less during exercise • Both relative and absolute intensity • Gradual loss of contractile strength due to • dec Ca ATPase and myosin ATPase activities and myocardial ischemia • Often, heart wall stiffens, delaying ventricular filling - dec SV… dec Q • The elasticity of blood vessels and the heart  due to connective tissue changes. • Heart mass usually  and there are fibrotic changes in the heart valves • Vascular stiffness  the peripheral resistance,  the afterload of the heart. •  peripheral resistance also raises SBP during rest and exercise (no change in DBP).

21. A-V O2 difference • Dec with age - contributing to dec aerobic capacity • Decreases from 16 vol % (20 yrs) to 12 vol % (65 yrs) ( mlO2/dl) • Reductions due to •  fiber/capillary ratio •  total hemoglobin •  respiratory capacity of muscle •  in muscle mito mass •  oxidative enzymes • However, A-VO2 is higher at any absolute exercise intensity with age • Capacity of autonomic reflexes that control blood flow is reduced

22. Skeletal Muscle • Loss of muscle mass and strength can severely impact quality of life • Muscle strength decreases approximately 8% per decade after the age of 45. • Aging results in a  in isometric and dynamic strength and speed of movement. • Strength losses are due to: •  size and # of muscle fibers • atrophy or loss of type II fibers •  in the respiratory capacity of muscle •  in connective tissue and fat • Eg sarcopenia

23. Muscle Fiber Types • With age there is a selective loss of type II fibers, •  is more rapid in the lower body. •  available strength and power. • The mechanisms involved in muscle contraction are also impaired: • less excitable, greater refractory period • [ ] of ATP and CP are • maximum contractile velocity  • There is loss of biochemical capacity with age. •  in glycolytic enzymes (LDH). • There are no changes or slight  in oxidative enzymes • *Controversy over whether there is a decrease in oxidative capacity or not with ageing • Relative strength  with training are similar in young and old individuals. • Only short term studies available

24. Training Response • Older people readily respond to endurance and strength training • Endurance Training helps • Maintain CV function • Enhances exercise capacity • Reduces risks for heart disease, diabetes, insulin resistance and some cancers • Strength training • Helps prevent loss of muscle mass and strength • Prevents bone mineral loss • Improves postural stability reduces risks of falls and fractures • Mobility exercises improve flexibility and joint health • Training also provides psychological benefits • Improved cognitive function, reduced depression and enhanced self efficacy • Training does not retard the aging process, it just allows the person to perform at a higher level - Fig 32.2

25. Endurance Training • Similar improvements in Aerobic capacity for young and old • 6 months ~20% increase in VO2max • Observe • Dec submax HR at absolute load • Dec resting and submax SBP • Faster recovery of HR • Improvements in ECG abnormalities • Inc SV and Q • Elderly require a VO2max of ~20 ml/Kg for an independent lifestyle • A conservative well structured program can bring most elderly to this level of fitness within ~3 months

26. Exercise Prescription • The principles of exercise prescription are the same for everyone, • however caution must be taken with the elderly to  the risk of injury. • Elderly have more abnormal ECG’s during exercise. • Start slowly with walking and swimming - low impact exercises • Running, racket-ball… only when fit • Problems with using estimates of Max HR for prescribing intensity • considerably variation in the elderly • (Max HR range : 105 - 200 for 60yr olds) • Principles • Progress carefully with intensity and duration • Warm up slowly and carefully • Cool down slowly - to less than 100bpm • Stretching - reduce DOMS