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Work PhysiologyA.H. Mehrparvar, M.D.
Yazd University of Medical SciencesDepartment of Occupational Medicine
Metabolism A set of chemical processes allowing cells
to live Nutrients: carbohydrates, lipids, proteins ATP:
energy currency of the body exists in all cells Two energetic bonds Each mole: 12000 calories
Metabolism Two kinds: Anaerobic (only for carbohydrates):
Phosphagen system Reserved ATP (for 1-2s) Phosphocreatine (for 5-8s)
Glycolysis (for 1 m.) Each molecule of glucose: 2 ATP Each molecule of glycogen: 3 ATP
Aerobic (carbohydrates, lipids, proteins)
Comparing different systems
Endurance: Phosphagen:8-10 s Glycogen: 1-2m Aerobic: unlimited
ATP production in unit time: 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:
calorie (gram calorie): energy needed to 1°C increase the temperature of 1g water
Calorie (KC): 1000 calories
Energy sources: Carbohydrates: 45% Lipids: 40% Proteins: 15%
Energy requirements: BMR + ADL + leisure activities +
work activities
BMR = 1650 KC: dependent on: 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.:
About 50% after 1 minute Muscle endurance: Dependent on:
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
At the biginning of activity:1. Anaerobic metabolism2. Aerobic metabolism of carbohydrates3. Aerobic metabolism of lipids (after 4-5 h)4. Aerobic metabolism of proteins5. 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.
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%)
Measurement of metabolism Direct calorimetry
Measurement of heat produced Indirect calorimetry
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
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
Sedentary work (<2 met) Lifting less than 4.5 kg, office work, work with
light objects Light work (2-3 met)
Lifting less than 9 kg, frequent lifting of objects <4.5 kg
Medium work (4-5 met) Lifting less than 23 kg, frequent lifting of
objects <11 kg
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