EFFECT OF HYPOXIA ON THE ADRENOCORTICAL RESPONSE TO EXERCISE IN MAN

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Abstract
Evidence was obtained of the importance of relative work load (%.hivin.VO2, max) in eliciting an adrenocortical response to exercise, by comparing the changes in plasma cortisol at a given work load under normoxic and hypoxic conditions. Normal male volunteers (5) aged 20-45 yr were studied. Although O2 consumption was lower in hypoxia than normoxia, relative work load was higher. Only in the hypoxic experiments was a significant rise in plasma cortisol observed, even though the treadmill speed and inclination settings were the same for each of a pair of experiments. The increased physiological demand of exercise in hypoxia is shown by the higher heart rates in this condition. One subject breathed the hypoxia mixture while at rest for 70 min during which time his plasma cortisol did not change significantly. This observation and the rise in plasma cortisol occurring only during the later part of the hypoxic experiments suggests that hypoxia itself is not the stimulus for adrenocortical activation. The trigger which activates the hypothalamic-pituitary-adrenal system is probably the same during hypoxic and normoxic conditions. It is apparently a function of relative work load.

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