Exercise does not directly increase or decrease fertility. Rather exercise affects other things that can increase or decrease fertility, exercise is in a sense an intermediary.
How does exercise increase female fertility?
Fertility in women is strongly affected by hormones. The more body fat a woman has the more estrogen those fat cells can produce. If the body has a high level of estrogen, it will not ovulate. This is why many birth control pills contain estrogen. Estrogen also acts to thicken the uterine walls to provide a home for fertilized eggs, however too much estrogen can cause this wall to become too thick making it difficult for eggs to implant. Exercise reduces body fat, in turn helping to establish healthy estrogen levels, which leads to proper ovulation and more ideal conditions for fertilized egg implantation. About 12% of infertility cases are a result of weight issues.
Exercise also is an effective method of relieving stress. Stress can lead to depression and interrupted or irregular menstruation. Both of which decrease your chances of becoming pregnant.
Can exercise decrease female fertility?
On the flip side of this coin too much exercise can also decrease fertility. As stated estrogen is produced by fat cells, and estrogen is essential in the production and release of eggs, and the ripening and preparation of the body for pregnancy. If a woman has too little body, fat not enough estrogen will be produced which can lead to infertility.
On top of this strenuous exercise and/or intense aerobic exercise reduces the production of progesterone and affects menstruation. Progesterone prevents the body from menstruating after an embryo has implanted without it pregnancy is not possible. Some recent studies also show that excess exercise leaves the body too drained to make the necessary changes for pregnancy.
What about exercise and male fertility?
Intense exercise has been shown to decrease fertility in men. Exercise reduces the level of testosterone in the male body, which results in less sperm. However moderate exercise helps keep the body healthy which means healthier sperm. Though studies are inconclusive, it is suggested that high body fat levels may also lead to infertility in men. Reasons for this are unknown. One suggested cause is an inability to penetrate as deeply resulting in a further swim for sperm to reach the egg. Certain sexual positions may remedy this. You can read more about those here.inability to penetrate as deep resulting in a further swim for sperm to meet the egg.
In short, moderate exercise will help maintain a healthy body weight, hormone levels, and stress level in both sexes, which will lead to increase fertility. In both cases, extreme or excess exercise may result in the opposite or infertility.
Estrogen and Fertility
Exercise and Fertility
Too Much Exercise and Pregnancy
Progesterone and Fertility
Effects of Excess Exercise on Fertility
Exercise and Male Fertility
Obesity and Fertility in Men