Gonadal hormones and semen quality in male runners: A volume threshold effect of endurance training

Eleven high mileage runners (HR) (108.0 ± 4.5 km·wk^-1), 9 moderate mileage runners (MR) (54.2 ± 3.7 km·wk^-1) and 10 sedentary controls (SC) of similar age (28.3 ± 1.5 yr) were studied to evaluate the effects of volume of endurance training on reproductive function in male runners. Levels of reproductive, adrenal and thyroid hormones were measured during a 1-hr period of serial blood sampling (q20 min) and urinary excretion of 24-hr luteinizing hormone (uLH) was determined on two separate days. Semen exams and sperm penetration of standard cervical mucus (Penetrak) were performed 2-5 times. Levels of total testosterone (TT) and free testosterone (FT) were significantly lower in HR (15.3 ± 1.3 nmol·l^-1 and 60.2 ± 5.1 pmol·l^-1) compared to MR (21.4 ± 1.6 nmol·l^-1 and 86.0 ± 6.1 pmol·l^-1) and SC (19.5 ± 0.9 nmol·l^-1 and 75.9 ± 3.6 pmol·l^-1). No differences (p > 0.05) were found in uLH, serum LH, follicle-stimulating hormone (FSH), and prolactin (PRL) among the three groups. No other hormonal differences (p > 0.05) were observed among the groups. Total motile sperm count and density were lower (p < 0.05) in HR than SC. Decreased (p < 0.0006) sperm motility and an increased (p < 0.004) population of immature sperm and round cells were observed in HR compared to MR and SC. Sperm penetration of bovine cervical mucus was also decreased (p < 0.024) in HR compared to SC. Volume of training, defined by km·wk^-1 run, was significantly correlated to sperm motility, density and number of round cells. TT was significantly correlated to number of round cells. These findings suggest that well defined differences in reproductive function exist between HR and MR, including decreased gonadal steroids and disturbed semen quality that is not observed in runners participating in more moderate volumes of training. Thus, a 'volume-threshold' effect of training is apparently coincident with high volumes of endurance running.