1. Copyright Catherine M. Burns
WORK PHYSIOLOGY
Copyright Catherine M. Burns

2. Copyright Catherine M. Burns
Work Physiology
more a discussion of the “energy” side of using muscles
rather than the “mechanics/force” side you see in biomechanics
extends to metabolism, energy restrictions on work and fatigue
Copyright Catherine M. Burns

3. Copyright Catherine M. Burns
Muscle Structure
Wickens Figure 12.1
Muscle, muscle fibre, myofibril, sarcomere
sarcomere
myofibril
muscle fiber
muscle
Copyright Catherine M. Burns

4. Sarcomere Construction
Two types of proteins actin (thin) and myosin (thick)
Actin filaments slide over myosin filaments to produce the contraction
Sliding filament theory of muscle contraction
long
short
z-line
Copyright Catherine M. Burns
myosin
actin

5. Aerobic and Anaerobic Metabolism
Aerobic (Oxidative Phosphorylation)
energy
ATP
muscles/work
nutrients OP
oxygen
CO2
Anaerobic (Anaerobic Glycolysis)
ATP
muscles/work
glucose AG
energy
lactic acid
Copyright Catherine M. Burns

6. Copyright Catherine M. Burns
Anaerobic Metabolism
Lactic acid causes muscle pain and fatigue
Anaerobic processes occur
at the start of work (first 1-3 minutes)
during heavy work
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7. Copyright Catherine M. Burns
Muscle Efficiency
Muscle efficiency is only about 20%
The rest is lost as heat
Increases body temperature
Problems in working in hot environments
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8. Copyright Catherine M. Burns
Circulatory System
blood delivers nutrients and oxygen to the muscles
carries away carbon dioxide and waste products
heart - pressure generating blood pump
lungs - site of oxygen and CO2 exchange
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9. Copyright Catherine M. Burns
Heart Parameters
change with work, heat, stress
Major measures
cardiac output (Q): flow rate of blood through the heart
5L/min resting
15L/min moderate work
25L/min heavy work
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10. Copyright Catherine M. Burns
Heart Measures
Cardiac Output
function of heart rate (HR) x stroke volume (SV)
Q=HRxSV
Heart rate: beats per minute
Stroke volume: litres of blood per beat
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11. Blood Flow Distribution
Changes with work
increases to muscles
more to skin in hot environments
consistent amount to brain
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12. Copyright Catherine M. Burns
Respiratory System
Air exchange system
Measures
tidal volume: amount of air breathed per breath
0.5L resting
2L heavy work
minute volume: amount of air per minute
tidal volume x frequency
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13. Copyright Catherine M. Burns
Energy Cost of Work
Basal metabolic rate: lowest level of energy expenditure needed to maintain life
kcal/day
varies with gender, age, weight
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14. Copyright Catherine M. Burns
Working metabolism: the increase in metabolism from resting to working level
Metabolic rate during work: sum of basal metabolic rate and working metabolic rate
range: 1.6 to 16 kcal/min
sitting 1.6 kcal/min, walking 2.8 kcal/min
heavy work 5kcal and up
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15. Measuring Physical Work
oxygen consumption rate
heart rate
linear relation between oxygen consumption and energy expenditure
see Figure 12.4
Copyright Catherine M. Burns

16. Physical Work Capacity
short term work capacity
also called “aerobic capacity”
about 15kcal/min men 10 kcal/min women
long term work capacity
suggested not over 1/3 of short term for 8 hrs
higher than this causes fatigue
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17. Copyright Catherine M. Burns
Fatigue
in this sense, body exceeds what can be provided by aerobic metabolism
anaerobic metabolism meets energy needs
decreased blood glucose
increased lactic acid
also psychological and health factors
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18. Designed Rest Schedules
formula p. 269
increased rest with heat (Figure 12.7)
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19. Copyright Catherine M. Burns