Endurance exercise training and reproductive endocrine dysfunction in men:Alterations in the hypothalamic-pituitary-testicular axis

Research indicates that endurance exercise training has significant effects upon the reproductive endocrine system of humans. Until recently, this eff ect was thought to be limited primarily to women. However, a growing body o f evidence demonstrates that the male reproductive endocrine system is also effected. Specifically, the circulating hormonal levels of testosterone ar e found to be at low concentrations; and, the hypothalamic-pituitary-testic ular axis that regulates testosterone production is altered in endurance tr ained men. The physiological mechanism inducing the lower testosterone is c urrently unclear; but in many respects, these men display hypogonadotropic hypogonadism characteristics. Currently, the time course of the changes in the reproductive endocrine system is unresolved and in need of much further s scientific investigation. The evidence available, however, suggests that a slowly developing process requiring years of exercise training results in these changes. Potentially, the lowered testosterone levels of the enduran ce-trained male could disrupt some of their anabolic or androgenic dependen t processes. To date, there are only a limited number of findings suggestin g that a consistent disruption of testosterone dependent processes occur du e to endurance exercise training (e.g., oligo-spermatogenesis). Conversely, the alterations in testosterone concentration brought about by endurance t raining could have cardiovascular protective effects and thus be beneficial to the health of these men.