Men who exercise (moderately or vigorously) at least 15 hours per week have sperm counts that are 73% higher than those of men who get little or no exercise, according to researchers at Harvard’s School of Public Health. At the same time, men who watch 20 or more hours of television have sperm counts that are half of those of men who hardly watch TV.

This fits right in with the steady, worldwide decline in sperm quantity and quality. Another factor here could be that watching TV isn’t usually the most romantic of activities. Time spent in front of the TV is time you’re not going to be spending having sex. And there’s plenty of evidence that, contrary to popular belief, frequent sex increases sperm production and quality.

If you’re not already a regular exerciser, don’t go overboard. Injuring yourself could put you right back on the couch, where you’ll be stuck watching too much TV again. Plus, there’s some research that suggests that overexercising could also reduce sperm quality.

The study was just published in the British Journal of Sports Medicine.