Overtraining affects male reproductive status*

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 × 10⁶) decreased significantly by 43% immediately after overtraining (52 ± 6.8 × 10⁶) and by 52% 3 months after overtraining (44.5 ± 20 × 10⁶). 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.