Exercise performed in different amounts and frequencies has varying effects on male and female fertility. The complex relationship between exercise and reproductive potential is likely due to alterations in the hypothalamic-pituitary axis. Extreme exercise may lead to anovulation and infertility, whereas exercise may result in improved ovulation and fertility in anovulatory obese patients. A large Norwegian study found that women who were active daily were 3.2 times more likely to have fertility problems than inactive women. Additionally, in women who exercised a moderate amount (either 16–30 min or 30–60 min), the risk of infertility was decreased compared to women who exercised < 15 min a day. Exercising to exhaustion was associated with an increased risk of infertility. The Nurses’ Health Study found that vigorous exercise for a minimum of 30 minutes a day was also associated with a decrease in ovulatory disorder infertility.
In contrast, regular exercise does not appear to affect semen parameters. A prospective study of men found that none of the semen parameters were altered with regular exercise, except bicycling >/= 5 hours a week was associated with low sperm concentration and low total motile sperm.