Chronoendocrinological studies in athletes. Circadian rhythms of T3, TSH, cortisol and testosterone.

Endocrine functions were studied in 83 healthy athletes, maintained under normal light-dark conditions, with normal activity-sleep patterns. In these subjects statistically significant circadian rhythms of T3, TSH, cortisol (CSL) and testosterone (T) were found; for each hormone two or three different types of circadian rhythm (with peaks of acrophase between: 6.30 a.m. and 1.30 a.m., 1.30 p.m. and 10.30 p.m., 10.30 p.m. and 6.30 p.m.) were observed. The following correlations have been demonstrated between the length of participation (in years) in performance sports and the mean circadian blood hormone concentration: a negative one for CSL (p less than 0.01) and a positive one for TSH (p less than 0.05). An increase of the mean circadian values of T concentration in venous blood was found in females fencers (n = 9).