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

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Muscular Function Assessment
Gallagher - OEH ch 21(CCW)
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Outline

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

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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

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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

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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

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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

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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)

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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

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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

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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

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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

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

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Exercise and Aging Skeletal Muscle

• Brooks - Ch 32
• Brooks - Ch 19 (p444-451)

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• 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

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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

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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

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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

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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

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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)

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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).

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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

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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

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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

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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

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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

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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