As a teenager I had the chance to play volleyball at a high level. Volleyball was my favorite sport and the one I excelled at. Yet I only trained 4 hours per week and played a match once a week (unless playing tournaments). Now things are very different for the current young athletes, they are expected to practice their sport for around 12-20 hours per week. To tell you the truth, I used to train as much but most of my training was done outside volleyball: I used to run a lot (10 km 4 times a week), play basketball & football, learn Aikido and play with my friends a lot. I was easily doing over 2 to 3 hours of sports every day except Sundays - In France everything is shut down on Sundays so it was our family/rest day. I never suffered any injury until recently (shoulder injury but nothing serious yet).

Nowadays Young athletes who specialise in one sport and train intensively have a significantly higher risk of stress fractures and other severe overuse injuries, even when compared with other injured athletes, according to the largest clinical study of its kind.

For example, young athletes who spent more hours per week than their age playing one sport – such as a 12-year-old who plays tennis 13 or more hours a week – were 70 percent more likely to experience serious overuse injuries than other injuries.

During a conference, Physician Dr. Neeru Jayanthi presented findings of his study titled “Risks of Specialized Training and Growth in Young Athletes: A Prospective Clinical Cohort Study.”

"We should be cautious about intense specialization in one sport before and during adolescence,” Jayanthi said. “Among the recommendations we can make, based on our findings, is that young athletes should not spend more hours per week in organized sports than their ages.”

Between 2010 and 2013, Jayanthi (and colleagues) enrolled 1,206 athletes ages between 8 to 18 who had come in for sports physicals or treatment for injuries. Researchers then followed each athlete for up to three years.

There were 859 total injuries, including 564 overuse injuries. The overuse injuries included 139 serious injuries such as stress fractures in the back or limbs, elbow ligament injuries and osteochondral injuries (injuries to cartilage and underlying bone). These serious injuries can force young athletes to be sidelined for one to six months or longer.

The study confirmed that specialising in a single sport increases the risk of overall injury. According to the study, young athletes are more likely to be injured if they spend more than twice as much time playing organised sports as they spend in unorganized free play -- for example, playing 11 hours of organized tennis each week, and only 5 hours of free play such as pick-up games.

The study offers the following tips to reduce the risk of injuries in young adults:

• Do not spend more hours per week than your age playing sports.
• Do not spend more than twice as much time playing organised sports as you spend in gym and unorganized play.
• Do not specialise in one sport before late adolescence.
• Do not play sports competitively year round. Take a break from competition for one-to-three months each year (not necessarily consecutively).
• Take at least one day off per week from training in sports.

The next step of that study is to test if many of these serious injuries are potentially preventable. Maybe the study will look at Federer who won Wimbledon at the age of 35 and after a 6 months period of rest...