Reproducibility of low resting testosterone concentrations in endurance trained men.

Previous reports indicate endurance trained (ET) men have low resting testosterone concentrations without any significant increases in their luteinizing hormone (LH) concentrations. The purpose of this study was to examine the reproducibility of these resting hormonal findings in ET men. Resting blood samples were collected at three separate trials (2 weeks apart) in groups of ET men (n = 15) and age-matched, untrained (UT, n = 13) men. Blood specimens were analyzed for total testosterone, LH, cortisol and prolactin. Results indicated that testosterone was significantly (p < 0.01) lower in ET than UT at each of the three trials. LH, cortisol, and prolactin were not different (p > 0.05) between the groups at any trial. These results confirm earlier findings reported for ET men. Furthermore, the results indicate the resting reproductive hormonal status (i.e., low testosterone) of ET men is reproducible and does not appear to be an artifact of the timing of the blood sampling methodology used.