WORK PHYSIOLOGY
Chapter 12 in your text
Copyright Catherine M.
Burns
1
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
2
Muscle Structure
 Wickens Figure 12.1
 Muscle, muscle fibre, myofibril, sarcomere
sarcomere
muscle
muscle fiber
myofibril
Copyright Catherine M. Burns
3
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 (contracted)
z-line
actin
myosin
Copyright Catherine M. Burns
4
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
5
Anaerobic Metabolism
 Lactic acid causes muscle pain and fatigue
 Anaerobic processes occur


at the start of work (first 1-3 minutes)
during heavy work
Copyright Catherine M. Burns
6
Muscle Efficiency
 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
7
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
Copyright Catherine M. Burns
8
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
9
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
Copyright Catherine M. Burns
10
Blood Flow Distribution




Changes with work
increases to muscles
more to skin in hot environments
Table 12.1


Resting muscles 15-20%
Heavy work 70-75%
 Also note temperature effect 40% of blood to skin
in the moderate work at 38 degree level
Copyright Catherine M. Burns
11
Respiratory System
 Air exchange system
 Measures

tidal volume: amount of air breathed per breath



minute ventilation: amount of air per minute


0.5L resting
2L heavy work
tidal volume x frequency
Body increases tidal volume first, then breathing
frequency
Copyright Catherine M. Burns
12
Total Lung Capacity
Residual Volume
(always there)
Residual Volume
(always there)
Vital Capacity (Maximum
Breathe in)
Tidal Volume (normal
breathe in, not max)
Expiratory Reserve
Volume
Inspiratory Reserve
Volume
Tidal volume ranges from 0.5L to 2L
Copyright Catherine M. Burns
13
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
14
 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
15
Measuring Physical Work
 oxygen consumption rate
 heart rate
 linear relation between heart rate and energy
expenditure
 see Figure 12.5
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
Figure 12.7 8 hour is about 40% of short term
 higher than this causes fatigue
Copyright Catherine M. Burns
17
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
18