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WORK PHYSIOLOGY Copyright Catherine M. Burns 1 Work Physiology • more a discussion of the “energy” side of using muscles • rather than the “mechanics/force” side you see in biomechanics • extends to metabolism, energy restrictions on work and fatigue Copyright Catherine M. Burns 2 Muscle Structure • Wickens Figure 12.1 • Muscle, muscle fibre, myofibril, sarcomere sarcomere muscle muscle fiber myofibril Copyright Catherine M. Burns 3 Sarcomere Construction • Two types of proteins actin (thin) and myosin (thick) • Actin filaments slide over myosin filaments to produce the contraction • Sliding filament theory of muscle contraction long short z-line Copyright Catherine M. Burns actin myosin 4 Aerobic and Anaerobic Metabolism • Aerobic (Oxidative Phosphorylation) nutrients energy ATP muscles/work OP oxygen CO2 • Anaerobic (Anaerobic Glycolysis) glucose AG energy ATP muscles/work lactic acid Copyright Catherine M. Burns 5 Anaerobic Metabolism • Lactic acid causes muscle pain and fatigue • Anaerobic processes occur – at the start of work (first 1-3 minutes) – during heavy work Copyright Catherine M. Burns 6 Muscle Efficiency • • • • Muscle efficiency is only about 20% The rest is lost as heat Increases body temperature Problems in working in hot environments Copyright Catherine M. Burns 7 Circulatory System • blood delivers nutrients and oxygen to the muscles • carries away carbon dioxide and waste products • heart - pressure generating blood pump • lungs - site of oxygen and CO2 exchange Copyright Catherine M. Burns 8 Heart Parameters • change with work, heat, stress • Major measures – cardiac output (Q): flow rate of blood through the heart • 5L/min resting • 15L/min moderate work • 25L/min heavy work Copyright Catherine M. Burns 9 Heart Measures • Cardiac Output – function of heart rate (HR) x stroke volume (SV) – Q=HRxSV – Heart rate: beats per minute – Stroke volume: litres of blood per beat Copyright Catherine M. Burns 10 Blood Flow Distribution • • • • Changes with work increases to muscles more to skin in hot environments consistent amount to brain Copyright Catherine M. Burns 11 Respiratory System • Air exchange system • Measures – tidal volume: amount of air breathed per breath • 0.5L resting • 2L heavy work – minute volume: amount of air per minute • tidal volume x frequency Copyright Catherine M. Burns 12 Energy Cost of Work • Basal metabolic rate: lowest level of energy expenditure needed to maintain life • 1600-1800 kcal/day • varies with gender, age, weight Copyright Catherine M. Burns 13 • Working metabolism: the increase in metabolism from resting to working level • Metabolic rate during work: sum of basal metabolic rate and working metabolic rate • range: 1.6 to 16 kcal/min • sitting 1.6 kcal/min, walking 2.8 kcal/min • heavy work 5kcal and up Copyright Catherine M. Burns 14 Measuring Physical Work • oxygen consumption rate • heart rate • linear relation between oxygen consumption and energy expenditure • see Figure 12.4 Copyright Catherine M. Burns 15 Physical Work Capacity • short term work capacity – also called “aerobic capacity” – about 15kcal/min men 10 kcal/min women • long term work capacity – suggested not over 1/3 of short term for 8 hrs • higher than this causes fatigue Copyright Catherine M. Burns 16 Fatigue • in this sense, body exceeds what can be provided by aerobic metabolism • anaerobic metabolism meets energy needs • decreased blood glucose • increased lactic acid • also psychological and health factors Copyright Catherine M. Burns 17 Designed Rest Schedules • formula p. 269 • increased rest with heat (Figure 12.7) Copyright Catherine M. Burns 18 Copyright Catherine M. Burns 19