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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: 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 Glycolysis (for 1 m.) 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: 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 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%) 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) Light work (2-3 met) 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) 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