BIOCHEMICAL AND HORMONAL CHANGES DURING A 1000 km ULTRAMARATHON

1. To examine individual hormonal responses to extreme physical stress, blood samples were taken from eight highly trained athletes 1 day before and within 15 min of finishing the 1986 1000 km Sydney to Melbourne Ultramarathon foot race. 2. The baseline hormonal state of these highly trained athletes was quite different from normal. Resting serum conjugated catecholamines — epinephrine (E), nor‐epinephrine (NE), dopamine (D), free E and free D — were significantly elevated above the normal mean (P < 0.01). ACTH levels were significantly elevated above the normal range. Immunoreactive β‐endorphin (IR‐βEP), growth hormone (GH), prolactin (PRL), testosterone, cortisol and cortisol‐binding globulin (CBG) were within the normal range. 3. The effect of the race on serum catecholamine levels was to elevate further free and conjugated NE (P < 0.01). Other catecholamines, free and conjugated, remained significantly elevated above the normal mean (P < 0.01). Adrenocorticotrophic hormone (ACTH) remained elevated, and IR‐βEP within the normal range, without significant change. A significant increase in GH (P < 0.05), PRL (P < 0.01), and cortisol (P < 0.01) was seen, with no change in CBG. 4. As a model of chronic physical stress, the ultramarathon runner demonstrates a significantly altered baseline hormonal state as reflected in the primary mediators of the stress response, the catecholamines and the hypothalamic‐pituitary‐adrenal axis. Their response to severe exercise is distinct from that of untrained individuals in whom conjugated catecholamines decrease and ACTH increase. This may represent hormonal adaptation to prolonged stress.