1. Work Physiology A.H. Mehrparvar, M.D. Yazd University of Medical Sciences Department of Occupational Medicine

2. 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

3. 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)

5. 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

6. Anaerobic metabolism  At the biginning of the activity  Low concentration of O2  1 mole glucose: 24000 calories (3%)  Glucose → pyrovic acid → lactic acid

7. 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)

8. Aerobic metabolism  More than 95% of energy  For short-time contractions: 50% from carbohydrates  For long-time contractions: mostly from lipids

9. 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

10.  Energy sources: Carbohydrates: 45% Lipids: 40% Proteins: 15%  Energy requirements: BMR + ADL + leisure activities + work activities

11.  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

12.  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

13. 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

14.  Metabolic systems in muscles (phosphagen, glycogen, aerobic)  Reconstruction of systems:  PK → ATP  Glycogen → PK and ATP  Aerobic → glycogen PK and ATP  O2 debt → aerobic

16.  At the biginning of activity: 1. Anaerobic metabolism 2. Aerobic metabolism of carbohydrates 3. Aerobic metabolism of lipids (after 4-5 h) 4. Aerobic metabolism of proteins 5. Anearobic metabolism

17. 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.

18. Respiratory system is not limiting during activities

19. 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%)

20.  Maximum heart rate: 220 – age  Effect of activity on maximum heart rate: ?

21. 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)

22. 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

23. 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

25.  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

26.  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