PITUITARY AND ADRENAL HORMONAL LEVELS CHANGE DURING 8 DAYS OF EXHAUSTIVE CYCLING BUT ARE UNRELATED TO PERFORMANCE DECREMENT

Introduction It has been suggested that changes within the pituitary and adrenal hormonal profile occur with exhaustive training and overreaching, since differences in adrenocorticotropic hormone (ACTH), growth hormone (GH), prolactin (PRL) and cortisol have been shown after training overload and in cross-sectional studies. Yet, data on the early alterations during intensified training is lacking. The goal of this study was to get insight in the hormonal changes during intensified training, and investigate if changes were related to changes in physical performance. Methods Thirty cyclists (mean±SD age 41±11 y, BMI 23.5±2.1 kg/m2 and VO2max 51.8±6.3 ml/kg/min) who participated in an 8-day cycling tour of 1,300 km with 18,500 climbing meters were included in this study. The external training load during the tour was approximately 900% relative to preparation. Morning and post-exercise serum and plasma samples were collected from the antecubital vein at the start, mid and end of the tour. Samples were analyzed for ACTH, GH, PRL and cortisol. Performance was measured before and after the tour by means of a maximal incremental cycle ergometer test. Subjects with a decrease in performance larger than the smallest worthwhile change (0.5% peak power output) were classified as functionally overreached (FOR), all others as acutely fatigued (AF). Mixed ANOVAs were used to test for effects of time (start, mid, end) and group (AF, FOR) on hormonal levels. Results One subject was excluded due to asthmatic symptoms during the exercise tests, 15 subjects were classified as FOR and 14 as AF. Morning ACTH (p<.01), cortisol (p=.01) and PRL (p<.01) were lower while GH (p=.03) was higher at the end compared to the start of the tour. In contrast, post-exercise cortisol (p<.01) and GH (p<.01) were higher at the end compared to the start of the tour. The ACTH:cortisol ratio was decreased both in the morning (p<.01) and post-exercise (p<.01). No differences between AF and FOR were observed for all measures. Discussion Pituitary and adrenal hormonal levels were generally decreased in the morning, whereas post-exercise levels increased during 8 days of intensified training. Yet, no differences between AF and FOR were found. This suggests that the observed changes in the pituitary and adrenal hormonal profile are a general response to intensified training, and that these hormones cannot be used for early distinction between AF and FOR. Contact [email protected]