Introduction: Although intensive, repeated and perennial, physical stress of training generally does not represent a health hazard to professional athletes. Adaptation to such stress is presumed on multiple levels, but still not fully defined. Our aim was to analyze specificities of hypothalamic-pituitary-adrenal (HPA) axis response and adaptation to physical stress in professional athletes.
Subjects and methods: We exposed 55 professional male athletes to acute physical stress by performing cardiopulmonary exercise test on a treadmill. Cortisol and ACTH responses were measured at 4 points: B at baseline (during rest), S at the start of the test (the moment of stepping on a treadmill), MAX at the point of maximal effort, and R at the 3rd minute of recovery period. Oxygen consumption (VO2) and heart frequency (f) were measured in parallel, as parameters of metabolic rate and cardiac function. Control group consisted of 20 sedentary male subjects matched by age. Statistical analysis was performed with SPSS software. Specifically, ANOVA for repeated measures was used to analyze difference in response.
Results: Although the athletes had higher baseline cortisol levels, cortisol response was attenuated during MAX compared to controls (P=0.010). Significant difference was also observed during R (P=0.015), with cortisol levels slowly declining in athletes, while they were still rising in controls. This was in line with significant difference in percent of change of cortisol level from S-MAX (P=0.010) and from MAX-R (P=0.015) between groups. Unlike cortisol, two groups had similar ACTH responses throughout the test (P>0.05 at all points), with levels still rising during observed recovery period in both groups. Apart from neuroendocrine adaptation, the athletes had higher VO2 (P<0.05) in all points in test except in anticipation S (P=0.740), and significantly lower f at B (P<0.01) and S (P=0.007). There was no correlation between VO2 and cortisol levels throughout test. On the other hand, cortisol values strongly correlated with f at S (P<0.05 for all values). Heart frequency at S was a significant independent predictor of all cortisol values (B was 0.399, 0.245, 0.309 and 0.286 for B, S, MAX and R cortisol respectively, with P being 0.001, 0.044, 0.010 and 0.023 respectively).
Conclusion: Adaptation of HPA axis to repeated physical stress might be protective against hypercortisolism. It is dependent of training status, and in line with autonomous nervous system adaptation. Adaptation of metabolic rate seems to be an independent form of adaptation.
18 - 21 May 2019
European Society of Endocrinology