Acute Hypothalamic–Pituitary–Adrenal Responses to the Stress of Treadmill Exercise

To study the effects of physical conditioning on the hypothalamic–pituitary–adrenal axis, we examined the plasma ACTH, cortisol, and lactate responses in sedentary subjects, moderately trained runners, and highly trained runners to graded levels of treadmill exercise (50, 70, and 90 percent of maximal oxygen uptake) and to intravenous ovine corticotropin-releasing hormone (1 μg per kilogram of body weight). Basal evening concentrations of ACTH and cortisol, but not of lactate, were elevated in highly trained runners as compared with sedentary subjects and moderately trained runners. Exercise-stimulated ACTH, cortisol, and lactate responses were similar in all groups and were proportional to the exercise intensity employed. These responses, however, were attenuated in the trained subjects when plotted against applied absolute workload. Only the highly trained group had diminished responses of ACTH and cortisol to ovine corticotropin-releasing hormone, consistent with sustained hypercortisolism. We conclude that physical conditioning is associated with a reduction in pituitary–adrenal activation in response to a given workload. Alterations of the hypothalamic–pituitary–adrenal axis consistent with mild hypercortisolism and similar to findings in depression and anorexia nervosa were found only in highly trained runners. Whether these alterations represent an adaptive change to the daily stress of strenuous exercise or a marker of a specific personality profile in highly trained athletes is unknown. (N Engl J Med 1987; 316:1309–15.), STRENUOUS exercise, a component of the primitive “fight or flight” response, is a challenge to homeostasis. Two chief stress-activated systems, the autonomic nervous system (with its endocrine component, the adrenal medulla) and the hypothalamic–pituitary–adrenal axis, are known to be modulated by exercise and to participate in the maintenance of homeostasis and the development of physical fitness.^{1 2 3 4 5 6 7 8 9 10} Physical training appears to lead to a reduction in the stress associated with any given workload. What part this modulation of the stress response plays in the improved performance of trained athletes remains an intriguing question. In an attempt to explore this question, we…