Objective: To substantiate the hypothesis that strenuous exercise disrupts the hypothalamic-pituitary-gonadal axis in men.
Design: Longitudinal study.
Setting: Normal human volunteers in an academic research environment.
Patients: Five endurance-trained men (maximum oxygen consumption 65.4 +/- 3.6 mL/kg per minute [means +/- SEM]) with normal spermatogenic and hormonal profiles.
Interventions: Semen and blood samples were collected bimonthly before, immediately after, and 3 months after overtraining, which was defined as twice the previous average weekly training volume with unchanged intensity.
Main outcome measure: Testosterone, cortisol, and sperm concentration.
Results: Basal T levels decreased to 5.37 +/- 67 ng/mL from 8.68 +/- 93 ng/mL (conversion factor to SI unit, 3.47) immediately after overtraining and basal cortisol levels increased to 215.3 +/- 31 ng/mL from 145.7 +/- 27 ng/mL (conversion factor to SI unit, 2.76). This inverse relationship was highly correlated (r = -0.92). Both cortisol and T levels returned to pretraining values 3 months after resumption of previous training volume. Sperm count (91 +/- 23.3 x 10(6)) decreased significantly by 43% immediately after overtraining (52 +/- 6.8 x 10(6)) and by 52% 3 months after overtraining (44.5 +/- 20 x 10(6)). However, all values remained within normal range and would not be expected to affect fertility.
Conclusions: Our results indicate that overtraining reduces T levels, which is highly correlated with an increase in levels of cortisol and possibly a subsequent decrease in sperm concentration 74 days later.