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.

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%)

Maximum heart rate:220 – age

Effect of activity on maximum heart rate:?

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

Heavy work (6-8 met) Lifting less than 45 kg, frequent lifting of

objects <23 kg Very heavy work

Lifting more than 45 kg, frequent lifting of objects >23 kg