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Exercise%20and%20Aging%20Skeletal%20Muscle

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Title: Exercise%20and%20Aging%20Skeletal%20Muscle


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 numbers 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 ECGs 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
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