Transcript WORK PHYSIOLOGY

WORK PHYSIOLOGY
Copyright Catherine M. Burns
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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
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Muscle Structure
• Wickens Figure 12.1
• Muscle, muscle fibre, myofibril, sarcomere
sarcomere
muscle
muscle fiber
myofibril
Copyright Catherine M. Burns
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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
actin
myosin
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Aerobic and Anaerobic
Metabolism
• Aerobic (Oxidative Phosphorylation)
nutrients
energy
ATP
muscles/work
OP
oxygen
CO2
• Anaerobic (Anaerobic Glycolysis)
glucose
AG
energy
ATP
muscles/work
lactic acid
Copyright Catherine M. Burns
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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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Muscle Efficiency
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Muscle efficiency is only about 20%
The rest is lost as heat
Increases body temperature
Problems in working in hot environments
Copyright Catherine M. Burns
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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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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
Copyright Catherine M. Burns
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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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Blood Flow Distribution
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Changes with work
increases to muscles
more to skin in hot environments
consistent amount to brain
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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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Energy Cost of Work
• Basal metabolic rate: lowest level of energy
expenditure needed to maintain life
• 1600-1800 kcal/day
• varies with gender, age, weight
Copyright Catherine M. Burns
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• 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
Copyright Catherine M. Burns
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Measuring Physical Work
• oxygen consumption rate
• heart rate
• linear relation between oxygen consumption
and energy expenditure
• see Figure 12.4
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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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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
Copyright Catherine M. Burns
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Designed Rest Schedules
• formula p. 269
• increased rest with heat (Figure 12.7)
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Copyright Catherine M. Burns
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