Copyright Catherine M. Burns 1 WORK PHYSIOLOGY Chapter 12 in your text
Copyright Catherine M. Burns2 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. Burns3 Muscle Structure Wickens Figure 12.1 Muscle, muscle fibre, myofibril, sarcomere muscle muscle fiber myofibril sarcomere
Copyright Catherine M. Burns4 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) myosin actin z-line
Copyright Catherine M. Burns5 Aerobic and Anaerobic Metabolism Aerobic (Oxidative Phosphorylation) nutrients oxygen energy ATP CO 2 muscles/work Anaerobic (Anaerobic Glycolysis) glucose OP AG energy lactic acid ATP muscles/work
Copyright Catherine M. Burns6 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. Burns7 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. Burns8 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 CO 2 exchange
Copyright Catherine M. Burns9 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. Burns10 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. Burns11 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. Burns12 Respiratory System Air exchange system Measures tidal volume: amount of air breathed per breath 0.5L resting 2L heavy work minute ventilation: amount of air per minute tidal volume x frequency Body increases tidal volume first, then breathing frequency
Copyright Catherine M. Burns13 Total Lung Capacity Residual Volume (always there) Vital Capacity (Maximum Breathe in) Tidal Volume (normal breathe in, not max) Inspiratory Reserve Volume Expiratory Reserve Volume Residual Volume (always there) Tidal volume ranges from 0.5L to 2L
Copyright Catherine M. Burns14 Energy Cost of Work Basal metabolic rate: lowest level of energy expenditure needed to maintain life kcal/day varies with gender, age, weight
Copyright Catherine M. Burns15 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. Burns16 Measuring Physical Work oxygen consumption rate heart rate linear relation between heart rate and energy expenditure see Figure 12.5
Copyright Catherine M. Burns17 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 hour is about 40% of short term higher than this causes fatigue
Copyright Catherine M. Burns18 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