WORK PHYSIOLOGY Chapter 12 in your text 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 (contracted) z-line actin myosin Copyright Catherine M. Burns 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 Table 12.1 Resting muscles 15-20% Heavy work 70-75% Also note temperature effect 40% of blood to skin in the moderate work at 38 degree level Copyright Catherine M. Burns 11 Respiratory System Air exchange system Measures tidal volume: amount of air breathed per breath minute ventilation: amount of air per minute 0.5L resting 2L heavy work tidal volume x frequency Body increases tidal volume first, then breathing frequency Copyright Catherine M. Burns 12 Total Lung Capacity Residual Volume (always there) Residual Volume (always there) Vital Capacity (Maximum Breathe in) Tidal Volume (normal breathe in, not max) Expiratory Reserve Volume Inspiratory Reserve Volume Tidal volume ranges from 0.5L to 2L Copyright Catherine M. Burns 13 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 14 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 15 Measuring Physical Work oxygen consumption rate heart rate linear relation between heart rate and energy expenditure see Figure 12.5 Copyright Catherine M. Burns 16 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 Figure 12.7 8 hour is about 40% of short term higher than this causes fatigue Copyright Catherine M. Burns 17 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 18