Several factors are of decisive importance for the individual's capacity to perform physical work: (1) energy output or motor power (aerobic energy yield and anaerobic energy yield); (2) neuromuscular function (strength and technique); and (3) psychological factors (tactics and motivation).
Depending on the nature of the demand of job, sport event, or leisure time activity, one, two, or all factors are of great importance. It is therefore impossible to present one formula that takes into account all aspects of the individual's performance capacity. Natural endowment probably has the dominating influence on the physical work capacity but by training and practice any of the factors may be improved.
Figure 1 presents an analysis of how the energy demand is covered during exhausting exercise; an experiment on a bicycle ergometer with a work load of 350 w is illustrated at left. From a mechanical efficiency of 22% the energy demand can be
Åstrand P. Physical Performance as a Function of Age. JAMA. 1968;205(11):729–733. doi:10.1001/jama.1968.03140370031007
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