Gonadotrophin-releasing hormone and human chorionic gonadotrophin tests reveal that both hypothalamic and testicular endocrine functions are suppressed during acute prolonged physical exercise.

The mechanism of suppression of gonadotrophins and testosterone during prolonged exercise was studied. Fourteen healthy males were injected immediately before an exhaustive bicycle run for 4 h, and before a control period without exercise, with one of the following substances: (1) 1 ml of saline, (2) 100 micrograms of a GnRH agonist (buserelin), and (3) 50 IU/kg of hCG. Each test was repeated for each subject 2 weeks apart, in a randomized single-blind fashion. Blood samples were taken before the injections (sample A), 6 h after the injections (sample B), and the following morning (sample C). During placebo treatment testosterone concentration decreased from A samples to B samples more in the exercise trial than in rest trial (31 vs 8%, P = 0.02). This exercise-associated decrease was reversed by both the GnRH agonist and hCG treatments. Serum gonadotrophin concentrations responded identically to GnRH agonist injections during exercise and rest trials. hCG resulted in a greater increase of serum testosterone from A to C samples at rest than during the exercise trial (52 vs 33%, P = 0.04). In conclusion, the exercise-induced suppression of serum testosterone is associated with two effects: suppressed endogenous GnRH stimulation of gonadotrophin release during exercise, and decreased testicular capacity to secrete testosterone during recovery period.

RCT Entities:   Population Interventions Outcomes