Gonadotropin decrease induced by prolonged exercise at about 55% of the VO2max in different phases of the menstrual cycle.

In order to evaluate the influence of physical exercise on the hypothalamic-pituitary-ovarian axis, we studied ten women in the early follicular phase (EFP), twelve in the late follicular phase (LEP) and nine in the luteal phase (LP). The test consisted of a 90-minute physical exercise on a motor driven treadmill at 55-60% of VO2max. Blood samples were taken before, during and after the test. Prolactin and cortisol did not increase in any phase. Estradiol showed a significant increase in LFP (from 361.5 +/- 110.6 to 472.7 +/- 138.9 pmol/L) and in LP (from 457.2 +/- 94.6 to 555.3 +/- 96.9 pmol/L) but not in EFP. Progesterone levels increased significantly only in LP (from 28.2 +/- 6.7 to 33.5 +/- 6.7 mmol/L): Luteinizing hormone (LH) levels decreased significantly in all phases: from 13.7 +/- 2.0 to 10.5 +/- 1.1 IU/L in EFP; from 14.6 +/- 2.1 to 11.5 +/- 1.9 IU/L in LFP and from 7.5 +/- 1.3 to 5.7 +/- 1.0 IU/L in LP, while follicle stimulating hormone (FSH) levels decreased only in LFP (from 8.1 +/- 0.5 to 6.7 +/- 0.6 IU/L). Our exercise protocol (prolonged, continuous and moderate) was able to cause a decrease in gonadotropins levels, and this phenomenon is not due to changes in the other tested hormones.