To understand whether excess exercise would alter hormones of HPO axis, we examined levels of HPO axis hormones
of the female rats. We found that rats had excess treadmill running in group E showed significantly reduction of GnRH, 17b-estradiol, and progesterone levels compared to controls ( p < 0.05), while EAMD or carbohydrate supplements
caused no changes in FSH and LH levels. Our finding is in consistent with other published reports from human studies,
such as in female athletes with long intensive physical training, the level of progesterone was only 1/3 of that in
normal control subjects, and the average estradiol level was also lower than controls. In addition, comparing different
sports, the long distance runners had the lowest level of estradiol and progesterone. Although the mechanism of
EAMD-induced damages of ovarian ultrastructure remains unclear, studies suggested that reduction of ovarian hormones
by exercise may be associated with the hypothalamic GnRH,which is known as an energy metabolism factor. The
reduction of GnRH release indirectly decreases the secretion of estradiol and progesterone.