For the current analysis, researchers analyzed thousands of sperm samples from hundreds of men who qualified to donate sperm based on their health history and semen quality. Donors needed healthy levels of three things that can make conception more likely: sperm concentration, or the amount of sperm released when men ejaculate; sperm morphology, meaning the ideal size and shape with an oval head and a long tail; and motility, or the ability of sperm to move through the female reproductive tract to reach an egg.

Men who got the most total exercise and logged the most time doing intense workouts had better sperm motility than men who got the least amounts of exercise, the study found.

“Regular exercise may improve semen quality parameters among healthy, non-infertile men,” said study co-author Dr. Yi-Xin Wang of Tongji Medical College of Huazhong University of Science and Technology in Wuhan, China, and the Harvard TH Chan School of Public Health in Boston.

“But it’s hard to tell how much exercise, and how often and what type of workouts should men do for optimal fertility,” Wang said by email.

All of the 746 study participants volunteered as potential sperm donors at the Hubei Province Human Sperm Bank in China. They were 28 years old, on average, and had a healthy weight, at least a high school education, no sexually transmitted diseases and no history of radiation exposure.

Researchers asked participants how often they exercised, and how intensely, as well as what other activities they did. Then, the study team scored participants’ exercise levels and intensity based on a measure known as metabolic equivalent of task (MET) minutes per week.

Light activities like walking or housework earn fewer points toward the total MET minutes per week than intense workouts like running or cycling.

Overall, half of the men in the study got at least 2,245.5 MET minutes a week. The least active men got only around 526.5 MET minutes, while the most active men got about 7,082.3 MET minutes.

While higher MET levels were associated with increased sperm motility, the men’s sperm concentration and morphology didn’t appear to vary based on how much exercise they got.

The amount of time men spent in sedentary pursuits like working at a computer or watching television also didn’t appear to impact any parameters of semen quality.

One drawback of the study is that it only measured activity levels at a single point in time. Another limitation is that researchers only focused on healthy men who were eligible to donate sperm.

Some previous research also suggests that excessive exercise is associated with infertility, said Dr. Muhammad Imran Omar, a researcher at the University of Aberdeen in the UK who wasn’t involved in the study.

“Therefore, it is important that the exercise should be done in moderation,” Omar said by email.

Even though the study didn’t find sedentary time associated with lower quality sperm, sitting too much is associated with other health problems like diabetes, obesity and heart disease that can in turn make it harder for couples to conceive, said Dr. Joan Khoo of Changi General Hospital in Singapore.

People who want to conceive should still try to limit sedentary time, Khoo, who wasn’t involved in the study, said by email.

“If your job is mostly sedentary, take every opportunity to get out of the chair or vehicle; stand, walk or climb stairs whenever you can,” Khoo advised. “Park the car some distance away or get down one bus stop earlier, and exercise as much as possible when not at work.”