THE EFFECT OF OVERTRAINING ON PLASMA-CORTISOL CONCENTRATIONS AT REST AND IN RESPONSE TO EXERCISE AND ADMINISTRATION OF SYNTHETIC ADRENOCORTICOTROPIN IN STANDARD-BRED RACEHORSES

The potential role of the hypothalamic-pituitary-adrenocortical axis i n the aetiopathogenesis of overtraining was investigated in a longitud inal training study. Plasma cortisol concentration was measured in Sta ndardbred geldings before and after high-intensity training (control g roup) or overtraining (treatment group) at rest, in response to an inc remental exercise test, and after ACTH administration. Resting cortiso l concentration and peak concentration after ACM administration did no t change throughout the study. Area under the curve (AUG) for cortisol concentration versus time over 2 hours post-ACTH injection decreased significantly for all horses over the study period, while the net rise (peak corrected for pre-injection concentration) decreased significan tly for the C group only (P<0.05). Peak cortisol concentration, AUC an d mean concentration over 2 hours after exercise decreased significant ly with overtraining (P<0.05). Further work may help to elucidate the potential value of the cortisol response to exercise in predicting the onset and monitoring recovery from overtraining.