The role of glucocorticoids in exercise.

From the literature we can make the following statements concerning the role of glucocorticoids in exercise and training. These conclusions are summarized graphically in Figure 3. 1. The principle physiological functions of glucocorticoids are stimulation of gluconeogenesis and mobilization of amino acids and fatty acids from body stores. 2. Injected glucocorticoids produce significant increases in the work produced by isolated muscle and by intact animals. 3. Light to moderate exercise work loads may produce an increase, decrease or no change in plasma glucocorticoid (GC) levels; depending on the degree of psychological and/or physiological stress involved in the exercise. 4. In moderate to exhaustive exercise the plasma GC levels progressively increase. In some subjects (especially animals) exhaustion produces a decrease in plasma GC which may represent a defense mechanism to prevent depletion of body resources. 5. Chronic exercise training produces adrenal cortex hypertrophy and usually a smaller rise in plasma GC during an acute exercise bout than that obtained with nontrained subjects. The resting GC levels frequently increase initially during training but return to normal as the trained state is reached. 6. The changes in GC response during training appear to be produced by decreased responsiveness of the adrenal cortex itself to ACTH stimulation and possibly by adaptation of the hypothalamus-hypophysis axis which reduces the ACTH released in response to stress. 7. The many combinations of psychological and physiological stress present in different exercise regimens probably account for the variety of GC responses to exercise reported in the literature.