WORK PHYSIOLOGY
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Transcript WORK PHYSIOLOGY
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