Thinking back to the summer his shoulder shut down, Scott Elsass 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.

Dr. Daniel D. Buss, founder of Sports and Orthopaedic Specialists, based in the Twin Cities, said he operates on a teenager at least once a week.

"Kids are doing more at younger ages. It's not unusual to see a fifth- or sixth-grader get hurt," said Buss, who specializes in shoulder and elbow disorders and is a team physician of the Minnesota Twins. "Kids are trying to do more complicated things for their skeletal maturity."

Time on the tennis court is a constant issue for Minneapolis Washburn boys' junior varsity coach Erik Telleen. His young teens can't get enough, but Telleen knows the consequences of too much. Sore elbows, shoulders and knees can lead to nagging injuries in the latter part of high school careers -- something the JV coach experienced himself.

"Ninth grade is about when you start to see kids experience some soreness in elbows," Telleen said. "A lot of my guys want to stay after practice and hit for hours and hours, and that is when you get injuries from overusage. These guys want to make it to the next level, so they're out hitting every night, and that's when I do have concerns."

Overcommitment doesn't always mean success, though. Mayo Clinic Sports Medicine Center athletic trainer Dan Christoffer said it can often produce the opposite result.

"If they start developing injuries in youth ball, by the time they get to high school they're not going to be effective at all and will have chronic ... injuries," Christoffer said. "It is becoming a lot more of an issue. A lot of these kids are singling out one sport."

Worst nightmare

Lying helpless on an operating table, Morgan Stippel saw her athletic career come to an end.

The fourth knee surgery of the Stillwater High student's life revealed another tear in the right anterior cruciate ligament.

The operation and anesthesia, once again, took a toll on the 18-year-old. She smiled at her mom in the recovery room and began describing a nightmare she had during surgery.

The mother's heart broke as her daughter, who played basketball, softball and volleyball since childhood, said she dreamed that the doctor found an ACL tear during the procedure intended to fix a torn meniscus.

"She said 'No, that was real,'" Stippel, now 19, recounted her mom saying.

The news only got worse. After Stippel learned she would need a fifth surgery and fourth ACL replacement (two in each knee), several doctors recommended she no longer play competitive sports.

"It felt like somebody had died. That's how upset I was about it," she said. "You go from running around your whole life, getting to the field on time, going to the gym, doing your workouts, lifting weights, and all the sudden you just have nothing."

Stippel, the first freshman to make the Stillwater varsity basketball team, pursued the sport year-round. But her first ACL tear sidelined her the next summer and haunted her through high school. The injury, Stippel believes, undoubtedly resulted from overuse.

"When you play year-round, those muscles never get a chance to rest and some doctors say that can lead to the injuries," said Stippel's dad, Roger, who's spent five years searching for answers. "If we keep using the same muscles and joints and tendons, we don't give them a chance to rejuvenate themselves."

Stippel never played a full season of high school basketball and missed all of her senior season. But she said playing athletics was worth it.

"I know likely at some point I'm going to need a knee replacement," she said after limping through the hall at her alma mater, still fresh off her fifth surgery. "If I look back on it, I would tell myself to [rest]. Based on my experience, I wouldn't play one sport year-round. Try to take a break."

Now a coach of youth basketball and softball players, she's pained when she sees them wearing knee, elbow and ankle sleeves and braces.

Enough already

Buss' staff regularly patrols the Web for medical news and studies, good and bad. After a recent study by the Journal of Athletic Training said that nearly 30 percent of all injuries are from overuse, the staff cringed when it stumbled upon news of a high school pitcher who threw more than 200 pitches in one game.

"It's disappointing in that you know how these kids get hurt," Buss said.

Last month at the Mall of America, Mayo's Healthy Living Clinic held a throwing camp to teach athletes how to avoid injury and improve throwing mechanics. The clinic also offers weekly opportunities for injury assessments and exercise training.

"Right now, youth sports is so big that we have to ... focus on prevention," said Chad Eickhoff, Mayo Clinic's supervisor of athletic trainer services. "How can we have those kids prevent overuse injuries and also injuries that cause problems when older in life?"

Buss' staff follows the same principles and avoids surgery at all costs. They believe the right mechanics and correct strength training provide the body with necessary tools to handle regular use.

"Overuse is an issue because there is just not enough time for them to rest." Eickhoff said. "Another part of the problem is not doing enough preventative exercises."

Throwing and "overhead" sports -- baseball, softball, volleyball, swimming, gymnastics, tennis -- lend themselves to more repetitive motion injuries, studies show.

For Elsass, that meant readjusting his shoulder for hitting serves and resting.

The adjustments have earned him a chance to play for the University of Nebraska's tennis team. But he wonders how much better he could have been if he had not overused.

"If I had to redo USTA stuff, I'd wait a year or two to get really intense about it. Since I was 10 or 11, I've been playing tournaments and competing," Elsass said. "Just see if that would have saved a little bit.

"You go to tournaments and see everyone taped up and kids serving underhand. It's frustrating."

Jason Gonzalez • 612-673-4494 Twitter: @JGonStrib