Alan 1
Hedge, Cornell University, August 2008
Work Capacity Evaluation
Professor Alan Hedge DEA 3250/6510
All mechanical work involves muscles. Muscular effort depends on:
Estimating Work Energy Demands
Together, the above define the pattern of work.
v Duration how long the continuous period of muscle contraction is (total time per minute that muscles are contracted) v Frequency how often the muscle contracts (number of work cycles per unit time). v Intensity the strength and oxygen requirements of work (light, moderate, heavy).
Dynamic work requires more blood but muscle activity aids blood flow to meet demand.
Energy Demands and Blood Flow Static Work
Muscle strength diminishes rapidly with static loading. Carbohydrates and fats are necessary for work and are burned to produce energy. Aerobic processes (aerobic glycolysis) - biochemical energy generating Anaerobic processes (anaerobic glycolysis) - biochemical energy
processes that require oxygen (O2). generating processes that dont require oxygen. Myoglobin molecule in muscle that stores oxygen that can be utilized for short, intense periods of work < 1 minute. Oxygen debt is the demand for oxygen at the start of muscle activity > oxygen from the circulatory system alone, because it takes time for the circulatory system to increase its supply. Oxygen debt is repaid after work ceases during a recovery time. Successful work design incorporates appropriate rest breaks.
Energy Processes
Oxygen Debt
Energy expenditure is measured in kilocalories (kcal) per minute = [70kcal 1 watt] Energy expenditure is ~ 5 times oxygen consumption in liters. Oxygen consumption correlates with work effort.
Energy Expenditure
Energy Demands of Work
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Alan Hedge, Cornell University, August 2008
Examples of typical energy demands of work (kcals/ minute) Work posture has a substantial effect on the energy expenditure of performing the same task. Use of supports reduces energy demands. How work is done determines the energy expenditure required by the activity. Estimated basal metabolic rate for an adult male is ~ 2,300 kcal/day. Estimated maximum energy output for an adult male is ~ 4,800 kcal/day. Consequently, estimated maximum work output for an adult male is ~ 2,500 kcal/day, which is ~ 5 kcal/minute. Recommended maintainable daily work output is 4 kcal/minute. Many work activities exceed 5 kcal/minute, so rest is needed to compensate.Rest time can be calculated from: R = (T(K-S))/(K-1.5)
R...