Work Physiology
An aspect of industrial engineering that takes into
account metabolic cost, measurement and
prevention of work strain, and other ergonomic
factors in the design of tasks and workplaces.
Answers.com
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Cardiovascular Anatomy
(Engineer’s Schematic)
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Metabolism
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Definition
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Transformation: chemical energy
work
Units of Measurement
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kilocalorie (kcal)
1 kcal = 1000 cal = 1 Cal
= heat required to raise 1 liter H2O
from 15 °C to 16 °C
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Units
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Common rate units: kcal/min
Alternate units: W = 1 joule/sec
1 W ≈ 0.014 kcal/min
1 kcal/min ≈ 73 W
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Cellular Metabolism (1)
carbohydrates
fatty acids
fats
proteins
glucose
digestion
amino acids
glycolysis
oxidation
deamination
pyruvic acid
acetic acid
deaminated AAs
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Cellular Metabolism (2)
carbohydrates
fatty acids
fats
proteins
glucose
digestion
amino acids
glycolysis
oxidation
deamination
pyruvic acid
acetic acid
deaminated AAs
CO2
energy
H2O
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Cellular Metabolism (3)
glucose
carbohydrates
fatty acids
fats
proteins
digestion
amino acids
glycolysis
oxidation
deamination
pyruvic acid
acetic acid
deaminated AAs
CO2
energy
adenosine triphosphate
H2O
adenosine diphosphate + PO4
creatine + PO4
creatine phosphate
Cellular Metabolism
(Summary)
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ADP + CP + energy (input) → ATP + Creatine + H2O
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ATP + Creatine + H2O → ADP + CP + energy (output)
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Muscle activity runs on energy derived from breakdown of ATP
to ADP. ATP is recharged by rebuilding from ADP with energy
from “combustion” of glucose, fatty acids and amino acids.
Aerobic Metabolism: adequate oxygen
Anaerobic Metabolism: inadequate oxygen, buildup of lactic
acid
Body Metabolism:
Components
Total Metabolism =
Basal Metabolism (life support)
+
Activity Metabolism (work, leisure activities)
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Basal Metabolism, Resting
Metabolism
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Basal Metabolism
– Male ( 70 kg )
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Female ( 60 kg )
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1400 kcal/day ≈ 1.0 kcal/min
Factors:
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1700 kcal/day ≈ kcal/min
Sex
Size
Age
Resting metabolism ~10% - 15% higher
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Metabolism
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Response to Exercise
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Factors Affecting Energy Expenditure
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↑ heart rate
↑ stroke volume
↑ artery-vein differential
blood distribution to muscles
oxygen debt (anaerobic metabolism)
Gender
Age
Training
Measurement
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Oxygen uptake (~4.8 kcal / 1.0 liter O2)
Heart rate (affected by many other factors)
Blood pressure (may be better for static work)
Subjective (e.g., Borg Ratings of Perceived Expenditure
scale)
Activity standards
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Energy Cost of Work
(Activity Standards)
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Grades of Physical Work
Wickens et al:
light
moderate
heavy
very heavy
extremely heavy
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Physical Work Capacity
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Aerobic capacity
≈ Short-term Maximum Physical Work Capacity
(MPWC)
≈ VO2max
see Fig. 12.6, p. 315
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VO2max = f(age, gender, health, fitness, training, …)
≈ 15 kcal/min, males
≈ 10.5 kcal/min, females
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NIOSH: 8-hour shift rate ≤ ⅓ MPWC
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Whole-Body Fatigue
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Symptoms
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Slight tiredness → weariness → complete
exhaustion
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Impaired muscle performance
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Falling asleep
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Exact nature & cause unknown
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Inability to reach steady state (@ 40-50% MPWC)
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Exacerbated by heat stress
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Whole-Body Fatigue
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Engineering controls
– Automation
– Workstation layout
Administrative controls
– Job rotation
– Work/rest scheduling
– Rest time:
T (K −S )
R=
K −1.5
R = rest time
T = total working time
K = work metabolic rate
S = standard metabolic rate
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Rest Time Examples
T = 60 min
K = 6 kcal/min
S = 4 kcal/min
T (K −S ) 60(6−4) 120
R=
=
=
≈27 min
K −1.5
6−1.5
4.5
T = 60 min
K = 10 kcal/min
S = 4 kcal/min
T (K −S ) 60(10−4) 360
R=
=
=
≈42 min
K −1.5
10−1.5
8.5
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Static Work & Muscle Fatigue
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Muscle contraction with minimal movement
Symptoms
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Discomfort, pain
Reduced coordination
Tremor
Injuries, accidents
Connective tissue damage
Causes
Impeded, occluded blood flow
– Anaerobic metabolism → lactic acid
Endurance = f(% MVC) [Maximum Voluntary Contraction]
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Static Work & Muscle Fatigue
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Engineering controls
Reduce loads
– Eliminate static postures
– Workstation layout
– Supports
– Use alternating muscle groups
Administrative controls
– Rest
– Job rotation
– Encourage postural changes
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