How does exercise impact male fertility?
This should be an easy question to answer by looking at the scientific evidence, but it’s not.
To start with, there are about half as many studies on exercise and male fertility as there are about exercise and female fertility. This is common in reproduction. Then, lots of the studies on males don’t measure fertility; they measure sperm counts or other things from semen analysis, and we know that semen analysis is not a perfect predictor of pregnancy. Some studies also measure levels of the hormones that regulate reproductive function. There are only a few studies that actually measure pregnancy as the outcome.
Also, there’s a real hotch-potch of studies that use different types of exercise (e.g. general physical activity, running, walking) and different durations or intensities of exercise. This variation between studies makes it difficult to compare their results.
Plus, some studies are in groups of men who seem to be infertile (i.e., their partner has not become pregnant despite at least 12 months of trying) or are seeking help for infertility, and others are in men whose fertility is assumed to be OK.
To make matters even more confusing, in recent years, there have been a few studies by a couple of researchers that have been questioned because of unethical conduct, and the researchers can’t provide the original data. These studies have been cited in at least 65 other articles in medical journals, so the horse has already bolted: a lot of the recent scientific literature relating to exercise and male infertility is influenced by questionable research.
So, to answer the question…
The story of exercise and male fertility is like the story of Goldilocks and the three bears.
Low levels of physical activity are associated with poorer sperm quality. Higher levels of activity are associated with improvements in sperm quality up to a point. Excessive exercise, like what might be done by people training for marathons or the Olympics, can lower testosterone levels, reduce sperm quality and lead to infertility. However, a recent summary of studies that used pregnancy as the outcome concluded, “there is currently insufficient evidence to determine whether physical activity or sedentary behaviour is associated with spontaneous female or male fertility”.
So, if you don’t do enough exercise, or if you do too much, then your fertility might be badly affected. Moderate exercise – like what is suggested in the Physical activity and exercise guidelines for all Australians – should be juuust right.