The impact of prior evening exercise on endocrine awakening responses

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Travis Anderson (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Laurie Wideman

Abstract: Monitoring the physiological response to exercise is important for both competitive athletes and the general population. Cortisol is a steroid hormone that demonstrates a distinct diurnal and circadian rhythm and responds to acute exercise. A distinct portion of the circadian cortisol profile is observed immediately after nocturnal sleep offset, with cortisol concentrations increasing rapidly within 30-45 minutes from waking. Termed the cortisol awakening response (CAR), this distinct period has been studied extensively within psychoneuroendocrinology and is becoming increasingly popular within the exercise sciences. The CAR may be a uniquely important biological marker for monitoring physiological responses to exercise since it reflects both basal concentrations and responsiveness of the hypothalamic-pituitary-adrenal axis. Neurophysiological control of heart rate variability (HRV) demonstrates considerable cross-over with the neural structures that regulate the CAR and thus may be a useful noninvasive substitute or supplement to monitoring the CAR. Therefore, the purpose of this study was to investigate the effects of acute exercise on the endocrine (cortisol, cortisone) and HRV responses to awakening. Participants reported to the laboratory for screening, fitness testing, and body composition measures. Within 7-10 days, participants returned to the laboratory in the evening (18:00) and an intravenous catheter was placed for blood sampling every 15 minutes, concluding one hour after nocturnal sleep offset. In a randomized fashion, separated by eight weeks, participants completed either a one-hour exercise protocol (70-75% of maximal power output) on the cycle ergometer or a resting protocol within the environmental chamber and then stayed in the laboratory overnight. HRV was collected continuously, and saliva samples were collected through the evening until bedtime (22:00) and immediately after waking. Blood and saliva samples were assayed for cortisol, and post-waking saliva samples were assayed for cortisone (E). HRV was analyzed (high-frequency power) for the entire post-waking period and in 5-minute epochs immediately before each blood sample during the one-hour waking period. Mixed-effects models were used to determine the effect of exercise on the cortisol response post-waking in the blood (and associated indices: maximal change from waking [CARb?]; area under the curve (AUC) relative to a zero concentration [CARbAUCG]; AUC relative to the increase [CARbAUCI]), in saliva (and associated indices: maximal change from waking [CARs?]; AUC relative to a zero concentration [CARsAUCG]; AUC relative to the increase [CARsAUCI]), and the cortisone response post-waking (EAR; and associated indices: maximal change from waking [EARs?]; AUC relative to a zero concentration [EARsAUCG]; AUC relative to the increase [EARsAUCI]), and HRV response to awakening. In addition, models assessed the relation between cortisol responses to exercise and the CAR/EAR indices and compared the awakening response indices between biological compartments and hormones. Participants (N = 12, mean (SD): age = 23 (4.22) years; mass = 76.82 (8.67) kg; height = 175.57 (4.96) cm; VO2max = 48.94 (7.49) demonstrated an average exercise-induced increase in cortisol of 477.33%. Results demonstrated a negative effect for exercise condition when modeling the serum and salivary cortisol responses to awakening via a quadratic growth model (serum: ßCondition = -42.26 [95%CI = -64.52 to -20.01], p < 0.001; saliva: ßCondition = -11.55 [95%CI = -15.52 to -7.57], p < 0.001). Cortisone derivatives EARAUCG (ßEARsAUCG = 3.78 [95%CI = 2.61 to 4.95], p < 0.001) and EARAUCI (ßEARsAUCI = 2.32 [95%CI = 0.22 to 4.42], p = 0.030) were significantly associated with their blood cortisol counterpart, but none were related to the area under the curve of the cortisol response to exercise. Salivary cortisone demonstrated a response to awakening that had both initial concentration and linear change across time negatively affected by exercise (ßCondition = -11.07 [95%CI = - 15.70 to -6.45], p < 0.001; ßLinear*Condition = -53.45 [95%CI = -103.14 to -3.76], p < 0.001). There was no observed change in HRV across the waking period, but the log-transformed high-frequency power was significantly lowered on the morning after exercise (ßCondition =-0.24, [95%CI = -0.45 to -0.03], p = 0.028). The HRV response to awakening was not associated with CAR or EAR derivatives. These results suggest that cortisol concentrations in saliva and blood and cortisone concentrations in saliva are significantly lower the morning following a prior evening exercise session. These reduced concentrations may result from increased cellular uptake of cortisol or a physiological decrease in adrenal output to conserve resources for the following day. Moreover, these results demonstrate that cortisone indices may be a better indicator of blood cortisol indices than salivary cortisol. Thus, the EAR should be considered as an alternative to the CAR in future work. [This abstract has been edited to remove characters that will not display in this system. Please see the PDF for the full abstract.]

Additional Information

Language: English
Date: 2021
Cortisol, Cycling, Hormone, Sleep
Exercise $x Physiological aspects
Sleep $x Physiological aspects

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