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

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

3. 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. 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. 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. 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. 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. 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. 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. 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. 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. 12 Outline Aging introduction Aging process Physiological capacity and aging –CV and skeletal muscle only Exercise Prescription

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

14. 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. 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. 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. 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. 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. 19 Physiological Capacity Physiological functioning peaks ~ age 30 Table 32-3 ~.75 to 1 % decline per year after 30 –Declines in VO 2 max, Q max, strength,power, and neural function; also increases in body fat All positively impacted by training Maximal O 2 consumption and age –VO 2 max declines ~30% (age 20-65) –Fig 32-2 - (training and age vs VO 2 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  - adrenergic responsiveness (dec HR max)

20. 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. 21 A-V O2 difference Dec with age - contributing to dec aerobic capacity Decreases from 16 vol % (20 yrs) to 12 vol % (65 yrs) ( mlO 2 /dl) Reductions due to –  fiber/capillary ratio –  total hemoglobin –  respiratory capacity of muscle –  in muscle mito mass –  oxidative enzymes However, A-VO 2 is higher at any absolute exercise intensity with age Capacity of autonomic reflexes that control blood flow is reduced

22. 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. 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. 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. 25 Endurance Training Similar improvements in Aerobic capacity for young and old –6 months ~20% increase in VO 2 max 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 VO 2 max 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. 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