Testosterone and endurance exercise: development of the "exercise-hypogonadal male condition"

During the last 30 years a large number of research studies have been conducted examining reproductive endocrine dysfunction in exercising women. The number of similar studies examining men is still relatively small. Nevertheless, an increasing amount of research studies in men indicate endurance exercise training has significant effects upon the major male reproductive hormone, testosterone, and the hypothalamic-pituitary-testicular axis that regulates reproductive hormones. This review article addresses one reproductive endocrine dysfunction found in exercising men, what has been deemed the "exercise-hypogonadal male condition". Specifically, men with this condition exhibit basal (resting-state) free and total testosterone levels that are significantly and persistently reduced. The exact physiological mechanism inducing the reduction of testosterone is currently unclear, but is postulated to be a dysfunction (or perhaps a readjustment) within the hypothalamic-pituitary-testicular regulatory axis. The time course for the development of the "exercise-hypogonadal condition" or the threshold of exercise training necessary to induce the condition remains unresolved. The potential exists for these reduced testosterone levels within the exercise-hypogonadal male to disrupt and be detrimental to some anabolic or androgenic testosterone-dependent physiological processes. Unfortunately, extremely few research studies have addressed whether such processes are affected, and thus findings are inconclusive. Conversely, the alterations in testosterone levels brought about by endurance exercise training have the potential for cardiovascular protective effects and thus could be beneficial to the health of these men. Current evidence suggests this condition is limited to men who have been persistently involved in chronic endurance exercise training for extended periods of time (i.e., years). Many questions, however, regarding the male reproductive endocrine adaptive process to exercise and exercise training remain unanswered, necessitating the need for further research on this topic.