Feodor Vassilyev (1707-1782) fathered 69 children with one wife - she gave birth to 16 twins, seven triplets and four sets of quadruplets. That's the largest documented number of children born to one mother. Clearly, fertility wasn't an issue for that pair!

But these days, one in three couples has a hard time conceiving because of poor semen quality. That may be because of environmental pollutants, such as hormone-disrupting phthalates, according to a 2013 study that showed French men's sperm concentration declined 33 percent between 1989 and 2005.

It also looks like burgeoning obesity rates are a big part of the problem. Another study found that men with waistlines 40 inches and up had a 22 percent lower sperm count than those with waistlines under 37 inches. Seventy-four percent of men in the U.S. are overweight or obese! No wonder fertility levels have declined in the U.S. over the past 30 years!

Whatever the issue, a new study in the journal Reproduction shows that if you get yourself in shape, your sperm will follow. Researchers had sedentary men give semen samples before starting one of four, 24-week routines (moderate-intensity continuous training; high-intensity continuous training; high-intensity interval training; or remaining sedentary).

The biggest improvements happened in the moderate intensity group (running on a treadmill for 30 minutes, three to four days a week). They had 8.3 percent more semen volume; 12.4 percent higher sperm motility; 17.1 percent improved sperm shape; 14.1 percent more concentrated sperm; and 21.8 percent more sperm cells, on average!