Download Strength

Muscular Function Assessment
Gallagher - OEH ch 21(CCW)
1
Outline
• Muscle strength is a complex function that
can vary with the methods of assessment
• Definitions and introduction
• Assessment methods
• Variables impacting performance
2
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
3
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
4
•
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
5
•
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
6
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)
7
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
8
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
9
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
10
• IsokineticIsokinetic
testing
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
11
•
•
•
•
Outline
Aging introduction
Aging process
Physiological capacity and aging
– CV and skeletal muscle only
• Exercise Prescription
12
Exercise and Aging
Skeletal Muscle
•Brooks - Ch 32
•Brooks - Ch 19 (p444-451)
13
• 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)
14
•
Life expectancy, Span, and
Lifestyle (diet, exercise)
will influence
Morbidity
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
15
– Table 32-1
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
16
sedentary individuals as controls in experiments - eg
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,
17
toxins),
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
18
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 19
absolute intensity
Stroke Volume and Cardiac Output
(Q)to pump blood
Aging  the hearts capacity
•
• 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.
20
–  peripheral resistance also raises SBP during rest and
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
21
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
22
• With age there
is a selective
of type II fibers,
Muscle
FiberlossTypes
–  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
23
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
24
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
25
months
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
26