Men who want to start a family should consider turning off the television and picking up some weights.
A study in the British Journal of Sports Medicine found that young men who watch 20 hours of television or more a week have a 44 percent lower sperm count than those who watch little or no TV.
The study also says men who exercise for 15 or more hours a week at a moderate or vigorous pace have a 73 percent higher sperm count than those who exercise less than five hours a week.
The researchers looked at semen samples from 189 men between the ages of 18 and 22 who were living in New York state.
The experts point out that a lower sperm count does not mean a man is less fertile or less likely to father a child, but say physical activity does affect the quality of semen.