Exercise is a stressor that elicits responses within the hypothalamic-pituitary-adrenal (HPA) axis. Cortisol is a key hormonal component and major resultant of HPA activation. While the cortisol responses to sub-maximal and near-maximal exercise are well-known, the response of this hormone to supra-maximal exercise (i.e., exercise beyond 100% of the work output elicited by the maximal oxygen uptake [VO2max]) is not wellcharacterized. Therefore, this study was conducted to examine and characterize the cortisol responses to supra-maximal exercise. Ten male participants completed a 30-sec cycle-ergometry test at 175% VO2max (peak lactate [LA] = 11.6 ± 1.0 mM/L [Mean ± SD]) and two 90-sec cycle-ergometry tests at 135% VO2max (peak LA = 11.9 ± 1.3 mM/L) and 110% VO2max (peak LA =13.6 ± 0.8 mM/L), respectively. Blood cortisol was measured pre-exercise (resting), 3 minutes post-exercise, and 30 minutes post-exercise. Each participant also completed a control trial, during which no exercise was performed. Peak cortisol responses after exercise occurred at 30 min of recovery and were significantly (p < 0.001) different from respective preexercise and control values. However, the peak cortisol responses did not differ significantly from one another (175% = 19.7 ± 3.0, 135% = 24.0 ± 3.6, 110% = 22.1 ± 2.5 ug/dL; p > 0.05, respectively). These results are limited by a small sample size, but suggest a physiological ceiling with respect to the magnitude of the circulating cortisol response to supra-maximal exercise, beyond which no further increase is seen despite increasing exercise intensity. |
