Long hours on a bicycle can tone muscle and improve cardiovascular fitness. Obvious, right? But can all that time in a saddle the size of a slice of pizza also wreak havoc on a man’s reproductive health?

In short, maybe. But probably only if you ride five or more hours per week, and even if you do, you can take steps to minimize the risk.

Too much of a good thing?

"I think for bicycling in general, too much of a good thing applies," said Dr. Michael Homer, a reproductive endocrinologist and expert in infertility at the Reproductive Science Center of the San Francisco Bay Area.

Several studies have linked bicycling with issues including genital numbness, erectile dysfunction (ED) and sperm viability. While these studies show a possible connection between cycling and infertility, others found none. The general benefits of aerobic exercise, which is great for general wellness and sexual health, may mitigate some of the negative aspects of cycling.

"We don’t have a definitive answer to (whether cycling can cause infertility issues), but we have biological plausibility," Homer said. "We know that some men who bike