Influence of Timing and Intensity of Muscular Exercise on Temporal Patterns of Plasma Cortisol Levels

Abstract

Plasma concentrations of cortisol were measured in 9 subjects from 0800 h to 1800 h at 10-min intervals during resting periods and 5-min intervals during exercise and recovery. This was done to assess the effect of exercise on the patterns of plasma cortisol levels. At 1000 h, 90 min exercise at a moderate work level (55% of VOi max) produced a transient rise in plasma cortisol which averaged 11.9 εg/100 ml (SE ± 1.2) and introduced subsequent suppression of meal-related increase. At a lower work load (25% of V_O² max) a similar transient rise occurred, averaging 11.7εg/100 ml (SE ± 2.2); latency, rate of concentration change and magnitude we not significantly different from those at a moderate work load. A strenuous work level was required to produce a more rapid response with an increased secretion rate. When 90 min exercise at a moderate work level was performed at 1300 h, (i.e. coinciding with postprandial cortisol concentration peak), the increase in plasma cortisol concentration (1.3 εg/100 ml (SE ± 0.3)) was significantly lower than that induced by the same exercise performed in the morning. These results demonstrate that high plasma levels of cortisol diminish the subsequent stress response and that exercise-induced and meal-induced increases are not additive. (J Clin Endocrinol Metab40: 845, 1975)