Download Work Physiology

Work Physiology
A.H. Mehrparvar, M.D.
Yazd University of Medical Sciences
Department of Occupational Medicine
Metabolism
A set of chemical processes allowing cells
to live
 Nutrients: carbohydrates, lipids, proteins
 ATP:
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energy currency of the body
exists in all cells
Two energetic bonds
Each mole: 12000 calories
Metabolism
Two kinds:
 Anaerobic (only for carbohydrates):
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Phosphagen system
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Glycolysis (for 1 m.)
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Reserved ATP (for 1-2s)
Phosphocreatine (for 5-8s)
Each molecule of glucose: 2 ATP
Each molecule of glycogen: 3 ATP
Aerobic (carbohydrates, lipids, proteins)
Comparing different systems

Endurance:
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Phosphagen:8-10 s
Glycogen: 1-2m
Aerobic: unlimited
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ATP production in unit
time:
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Phosphagen: 4 moles
Glycogen: 2.5 moles
Aerobic: 1 mole
Anaerobic metabolism
At the biginning of the activity
 Low concentration of O2
 1 mole glucose: 24000 calories (3%)
 Glucose → pyrovic acid → lactic acid

Aerobic metabolism (carbohydrates)
Oxidative metabolism
 Glucose → pyrovic acid + 2 ATP
 Pyrovic acid → acetyl coA + H2O + CO2
 Acetyl coA → CO2 + H + 2 ATP (Krebs cycle)
 Oxidation of hydrogens (oxidative
phosphorylation): 30 ATP
 1 mole glucose: 686000 calories
 1 mole glucose: 38 ATP (456000 calories)

Aerobic metabolism
More than 95% of energy
 For short-time contractions: 50% from
carbohydrates
 For long-time contractions: mostly from
lipids

Metabolic rate
Heat produced by chemical reactions
 In average 27% of the energy of nutrients
is used (73% produces heat)
 Energy units:
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calorie (gram calorie): energy needed to 1°C
increase the temperature of 1g water
Calorie (KC): 1000 calories
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Energy sources:
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Carbohydrates: 45%
Lipids: 40%
Proteins: 15%
Energy requirements:
BMR + ADL + leisure activities +
work activities
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BMR = 1650 KC: dependent on:
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Height and weight
Age
Gender
Hormones
Temperature
sleep
+ Eating: 1850 KC
 + sitting: 2000-2250 KC
 Heavy working: 6000-7000 KC

BMR: 65-79 KC/h
 Sitting: 100 KC/h
 Standing: 105 KC/h
 Typing: 140 KC/h
 Walking: 200 KC/h
 Running: 570 KC/h
 Climbing stairs: 1100 KC/h

Musculoskeletal system during work
Maximum muscle power reduces during
work
 E.g.:
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About 50% after 1 minute
Muscle endurance:
 Dependent on:
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Muscle glycogen
Consuming carbohydrates
Metabolic systems in muscles
(phosphagen, glycogen, aerobic)
 Reconstruction of systems:
 PK → ATP
 Glycogen → PK and ATP
 Aerobic → glycogen PK and ATP
 O2 debt → aerobic
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1.
2.
3.
4.
5.
At the biginning of activity:
Anaerobic metabolism
Aerobic metabolism of carbohydrates
Aerobic metabolism of lipids (after 4-5 h)
Aerobic metabolism of proteins
Anearobic metabolism
Respiratory system during work
Average O2 consumption during rest:
250 mL/min.
 Activity: ↑ rate and depth of respiration
 Average O2 consumption during activity:
3600-5000 mL/min.
 Diffusion capacity of O2 during rest:
23 mL/min.
 Diffusion capacity of O2 during activity:
80 mL/min.

Respiratory system is not limiting during
activities
Cardiovascular system during work
Blood flow to muscles (rest): 3.6 mL/min
 Blood flow to muscles (work): 90 mL/min
 Cardiac output (rest): 5.5 L
 Cardiac output (work): 30 L
 During work:
 ↑ Blood flow to muscles
 ↑ stroke volume (50%)
 ↑ heart rate (270%)
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Maximum heart rate:
220 – age
 Effect of activity on maximum heart rate:
?
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Measurement of metabolism
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Direct calorimetry
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Measurement of heat produced
Indirect calorimetry
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Measurement of consumed O2
Consumption of O2 an estimate of consumed
energy
More than 95% of energy from aerobic
metabolism
1L consumed O2 → 4825 c energy (energy
equivalent of O2)
Physical capacity
Aerobic capacity: an estimate of physical
capacity
 Maximum heart rate: an estimate of
aerobic capacity esp. in average activities
 Maximum heart rate is not appropriate for
light or heavy work
 Maximum aerobic capacity: VO2max

VO2 max
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Amount of O2 consumed in the point of
maximal aerobic metabolism
Units:
 1 Met = 3.5 ml/Kg/min
 1 Met = 1 Kcal/Kg/hour
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Sedentary work (<2 met)
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Light work (2-3 met)
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Lifting less than 4.5 kg, office work, work with
light objects
Lifting less than 9 kg, frequent lifting of
objects <4.5 kg
Medium work (4-5 met)
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Lifting less than 23 kg, frequent lifting of
objects <11 kg
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Heavy work (6-8 met)
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Lifting less than 45 kg, frequent lifting of
objects <23 kg
Very heavy work
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Lifting more than 45 kg, frequent lifting of
objects >23 kg