Acute Exercise-induced Changes In The Cortisol Awakening Response

Abstract

The effects of acute exercise on the cortisol awakening response (CAR), characterized by the rapid increase in cortisol concentrations within the 30 - 45 minutes following sleep offset, have yet to be fully elucidated. PURPOSE: Thus, this study investigated the effects of late-evening acute exercise on the CAR the following morning. We hypothesized an altered cortisol concentration and dynamic during the post-awakening period, driven by the effect of prior evening exercise. METHODS: Twelve participants (mean (SD): age = 23 (4) y; mass = 76.8 (8.7) kg; height = 175.6 (5.0) cm; VO2max = 48.9 (7.5) ml.kg-1.min-1) reported to the laboratory in the evening (1800 h) on two occasions and completed, in random order, an exercise (70-75% of maximal power output) and rest condition. During the one-hour post-awakening period, blood and saliva samples were collected every 15 min and assayed later for cortisol via enzyme-linked immunoassay. Mixed-effects growth models determined the effect of exercise on the cortisol response post-waking in both blood and saliva. RESULTS: Expectedly, cortisol concentrations in both blood (βLinear = 234.89, [95%CI; 119.28, 350.50], p < 0.001; βQuadratic = -245.42, [-356.28, -134.56], p < 0.001, Conditional R2 = 0.705) and saliva (βLinear = 52.25, [29.93, 74.56], p < 0.001; βQuadratic = -42.04, [-63.44, -20.65], p < 0.001, Conditional R2 = 0.576) significantly increased, in a quadratic manner, during the post-awakening period. Additionally, the cortisol responses during the post awakening period were significantly lower following the exercise condition than the rest condition (serum, βCondition = -42.26 [-64.52, -20.01], p < 0.001; saliva, βCondition = -11.55 [-15.52, -7.57], p < 0.001). CONCLUSIONS: In support of our hypothesis, these results suggest that cortisol concentrations in both saliva and blood are significantly lower the morning following a prior evening exercise session. Lower CAR may result from increased cellular uptake of cortisol or a physiological decrease in adrenal output to conserve resources for the next day. We demonstrated that the CAR is sensitive to acute exercise bouts, and thus the CAR may serve as a useful biomarker to monitor responses to exercise training.