Study objective: To investigate the effects of two forms of exercise, endurance training (running) and resistance training (weight lifting), on reproductive function in male athletes.
Design: Cross-sectional study.
Setting: Reproductive Endocrinology and Exercise Laboratory.
Subjects: Twenty-eight healthy male volunteers, 18 to 35 years of age, including 10 endurance-trained runners, 8 resistance-trained weight-lifters, and 10 sedentary controls.
Main outcome measure(s): Hormonal evaluation included determination of plasma levels of total testosterone (T), serum levels of free T, luteinizing hormone (LH), follicle-stimulating hormone, prolactin, and estradiol, and urinary excretion of LH. Semen analyses included an evaluation of sperm characteristics in terms of density, count, motility, and morphology, and a determination of in vitro sperm penetration of standard bovine cervical mucus.
Results: Compared with sedentary controls, endurance-trained and resistance-trained athletes presented with significantly lower levels of total and free T. There were no significant differences in the serum levels of all other circulating and urinary hormone measurements among the three groups. Sperm density, motility, and morphology were significantly altered only in the endurance-trained runners. In vitro sperm penetration of standard cervical mucus was significantly reduced in the endurance-trained runners.
Conclusion: Both endurance and resistance training modify the male reproductive hormone profile in a similar manner; however, only endurance training, in the form of running, is associated with subclinical modifications in semen characteristics.