We’re surrounded by positive messages about exercising, yet there are surprisingly few quality studies that have looked at a potential link between exercise and fertility. We know that female athletes often have irregularities with their cycles, and that high levels of exercise seem to be associated with longer menstrual cycles. Research on fertility patients has been inconclusive – one study showed that moderate exercise was correlated with a lower likelihood of having a baby, another showed the opposite.
One of the better studies on the topic compared almost 4,000 Danish women between the ages of 18 and 40 who were trying to get pregnant. Those who reported more “vigorous” physical activity (i.e., >5h/week of running, fast cycling, aerobics, gynmastics, swimming) took longer to get pregnant, except for women with a Body Mass Index (BMI) >25, where vigorous exercise had a small positive effect. Women who engaged in more “moderate” exercise (e.g., brisk walking, leisurely cycling, golfing, gardening), had a slightly shorter time to pregnancy across all BMIs. The study tried to rule out other factors that could influence pregnancy outcomes but did not discuss a mechanism that could prevent pregnancy if women were engaged in vigorous exercise.
There’s also some research on the other half of the equation, sperm and exercise: Being sedentary is associated with lower sperm count and concentration – a study of ~200 men showed that the more they engaged in physical activity, the higher their sperm count was. However, it’s unclear from that study if there is a ceiling to exercise at which it has a negative effect on sperm (the participants didn’t go beyond 15h/week). Sedentariness has also been linked to erectile dysfunction in several studies.
If you’re trying to conceive or are preparing for fertility treatment, check with your doctor on their recommendations regarding exercise. For women, the above may be good news if you were concerned that exercising less vigorously during fertility treatment (e.g., doctors often recommend no activities involving jumping or twisting that could affect your ovaries) would have a negative effect. We hope that more research will be conducted on the topic to replicate the above findings and hone in on what possible mechanisms could be at play to affect outcomes.