Repetitive motions and no breaks can cause lifelong problems.

Thinking back to the summer his shoulder shut down, Scott Elsass, pictured above, now can easily understand why. The Eden Prairie tennis player chuckled as he explained how he hit balls several hours, every day, for six straight weeks.

Worn out, at age 16.

The repetitive motion of hitting serves over and over during his sophomore summer led to a shoulder injury that required nearly a year of healing. A nationally ranked player at age 14, he limped through the remainder of his high school career this spring and battled back to the state tournament finals in June.

“All that stuff was from overuse,” Elsass said. “The summer I injured my shoulder, I had played 41 out of 42 days in a row. I had five tournaments in that stretch.”

It’s a familiar, grueling physical toll to young athletes swept up in a sports culture that’s demanding specialization and year-round commitment at earlier-than-ever ages. As their training intensifies, injuries rooted in repetitive motion or overtaxed bodies are on the rise — and putting them at risk for longer-term problems as they grow older, according to local surgeons, sports medicine clinicians and several recently released national studies.