Altitude, training and human performance.

The effect of altitude on human performance is complex. Numerous variables are known to change from sea-level measures. Maximum aerobic power is depressed as ascent occurs and this impairs the ability to work maximally. While changes in haematological variables would theoretically counterbalance the loss in aerobic power, they have not been shown to do so. The environmental stress of cold may have positive effects on aerobic capacity at altitude, but this has been little investigated in humans. Pulmonary ventilation increases with altitude and the measure of hypoxic ventilatory response holds some promise of predicting humans who may benefit from altitude conditioning. Cardiac function is well maintained while lung function is not. The preferred fuel for exercise at altitude seems to be fat, while carbohydrate metabolism is dramatically changed. Much is not known of high altitude anorexia and muscle mass loss. Conditioning at altitude is known to benefit performance at altitude. The evidence for a sea-level benefit from altitude training as yet remains elusive. While selected individuals may benefit, the reasons why have not been determined.