Effects of endurance exercise on nocturnal hormone concentrations in males.

A preliminary study was conducted to evaluate the change in nocturnal concentrations of testosterone, luteinizing hormone, growth hormone, prolactin, thyroxine, and cortisol following a control day (no exercise) and on a day in which exercise was performed. Exercise consisted of 90 min of cycling at 70% of each subject's maximal oxygen uptake. The exercise occurred from 1630 to 1800 hr on the exercise day while a comparable period of rest took place on the control day. Hormonal concentrations were evaluated at 2-hr intervals for a 12-hr period each night (2000-0800 hr). The subjects slept from 2255 (+/- 20 min [X +/- S.E.M.]) until 0715 (+/- 15) during each night. All hormone responses were plotted and integrated for the 12-hr period. Analysis indicated that a significant augmentation of the prolactin and thyroxine responses occurred, while concurrently an attenuation of the growth hormone and cortisol responses were observed. Contrastingly, no significant effects were found for the testosterone and luteinizing hormones responses. The physiological significance of these findings remained to be determined, but the results do suggest that further research is warranted in the area.