There aren't many off seasons for seven year old Mason Ziegler.  He already plays in two football leagues and this fall plants to sign up for at least two more sports,  something his dad encourages.

Jason Ziegler, Mason's Father says "When I was younger I remember never being inside and you know, it's hard to get kids to go outside now, and I think it's just great to play as many sports as they can."

But not everyone has the same philosophy.  Today more kids than ever are sticking to just one sport.

Timothy Hewett, PhD, Wexner Medical Center says "You could call it the Tiger Woods syndrome. Young athletes feel like they have to play a single sport and they have to play it year round."

Tim Hewett is the head of sports medicine at Wexner Medical Center.  He says many athletes focus on just one sport hoping to gain an advantage over others.  But after following more than 500 athletes for more than a decade, Dr. Hewett found that specializing in one sport can be costly.

Timothy Hewett says ""What we observed was those that play a single sport  year found are at about 50 percent higher risk of going on to a knee injury."

Part of the problem is repetition.  Doing the same motions in the same sport year after year can wear out bones and joints.  But that's not all.  Hewett also found if a one sport athlete does injure a knee, they can also struggle with significant weight gain.  And not just immediately after the injury.

Timothy Hewett says "but even when we follow them over multiple years, ever 2, 3, 5 years out, they tend to retain that weight gain."

His advice is to play more than one sport, which can help build core strength and balance several muscle groups so one is not used consistently  more than others.  It's an idea Jason wants to stress to his kids now, so they can reap the benefits later.

Hewett looked specifically at young girls who play one sport.  His study found that after a knee injury, the risk of long term obesity jumped 33 percent, even if the girls recovered and were able to play their sport again.