Abstract

This study compares the resting reproductive hormonal profiles of untrained (N=11) and endurance-trained (N=11) males. Testosterone, free testosterone, estradiol, luteinizing hormone (LH), prolactin, and cortisol were measured by radioimmunoassay in resting blood samples (8 h fast) colleted every 60 min for 4 h. The endurance-trained group had been active for 12.4 +/- 6.7 yr, 6.6 +/- 0.2 d/wk, 68.5 +/- 4.4 min/d, while the untrained group was sedentary. Neither group had histories of hypothalamic-pituitary-testicular disorders. The overall 4 h mean testosterone and free testosterone levels were significantly lower in the trained group. The LH of the endurance-trained group was higher; however, LH pulse frequency and amplitude did not differ between groups. An enhanced estradiol feedback to the hypothalamus-pituitary could not account for the elevated LH, as estradiol levels were similar in the groups. Prolactin and cortisol levels were normal and did not differ between groups. The results suggested normal hypothalamic-pituitary function existed in the trained subjects, and prolactin and cortisol were not causative factors in the lowered resting testosterone and free testosterone levels. The findings indicate that chronic endurance training lowers testosterone and free testosterone in males possibly by impairing testicular function. Verf.-Referat