ABSTRACT
In sports events or strenuous exercise lasting more than one minute, the pre-
dominant mode of energy production is aerobic. This means that performance is
limited by the oxygen that is delivered to and utilized by the active muscles. The
level of performance is determined by the nature of training, which can affect
both central and peripheral physiological factors. When the muscles are well
trained, as in the case of elite endurance athletes, the limiting factors in determin-
ing the maximal oxygen uptake are the cardiac output and the oxygen-carrying
capacity of the blood. The maximal cardiac output is also highly important when
exercise is conducted in the heat because it then subserves two functions: the
distribution of blood to the skin for thermoregulatory purposes and the supply of
oxygen to the active muscles for energy metabolism.
