COLLEGE PARK, Md — A growing number of young athletes are focusing on playing a single sport, putting themselves at greater risk of serious injuries, physicians said.

“When athletes that play one sport and one sport alone, there’s probably more hours of competition in that one sport than there were competing if they had two or three other sports,” Maryland Terrapins team physician and assistant orthopaedics professor Dr. James Dreese said. “It’s the hours of competition that puts them most at risk for having those problems.”

Some parents believe that specialization can help their children become stars, earning a college scholarship or even a pro career. Over the past decade, sports performance scientist Dr. Chris Stankovich said he has noticed more and more children beginning to specialize in one sport.

“Culturally speaking, more and more kids are seeing that a friend of theirs or a schoolmate is doing one sport year-round, so it kind of normalizes it,” Stankovich said.

More than 44 million children in the United States participate in youth sports, according a 2008 survey by the National Council of Youth Sports. But only about 6 percent of high school athletes go on to play football, baseball or soccer in college, according to the NCAA. About 3 percent play college basketball.

Specialization at a young age, however, can set young athletes up for serious injuries.

For example, the throwing arm of a young baseball player who specializes in pitching too early can undergo major structural changes.

“There are some pretty significant adaptive changes that take place in the throwing shoulder with regards to the way it rotates and the way in which it’s orientated that is most related to the hours of which the athlete is throwing. The younger they are, the more that adaptive change tends to be,” Dreese said.

Reggie Zayas, the commissioner of the Marlboro Boys & Girls Club and a travel league in Upper Marlboro, Md., said that about 40 percent of his kids specialize in baseball, usually by ages 9 or 10.

“(Kids on travel-select leagues are) falling behind the curve if they play multiple sports,” Zayas said. “If you try to play (football, basketball and baseball) ... you’re falling behind the curve because there are so many kids just concentrating on one sport.”

Harry Hudson, the president of Henlopen Pop Warner and coach of the Cape Vikings pee-wee team in Lewes, Del., tells his players the same thing.

Hudson and his fellow coaches encourage kids under 12 to stay active and to participate in as many different sports as possible. But when they become teenagers, he advises them to consider specializing.

“When you move on to that middle school or that high school level, you need to start looking at your future,” Hudson said.

Some parents, like Hudson, view sport sampling as more dangerous than focusing on one sport.

“In football, you’re using your shoulders by hitting people. You’re using your legs also. You go into wrestling, and you’re not giving your body enough time to heal. Now you’re going right back into another sport that has to do with possible shoulder injuries,” Hudson said.

But doctors argue that playing only one sport is more dangerous.

The movement toward specialization may produce more successful athletes, but it also results in more injuries. More than 3.5 million children 14 and younger were treated for sports injuries in 2010, according to the American Academy of Orthopaedic Surgeons. In contrast, 1.9 million were treated in 2002, according to the Centers for Disease Control.

Researchers at Loyola University Chicago Stritch School of Medicine found in 2011 that single-sport athletes were almost twice as likely to injure themselves as multisport athletes.

“Certainly, if you’re throwing a baseball 10, 11, 12 months a year, you’re going to have a much higher risk of injury than if you’re throwing four, five months a year and maybe throwing a football a few months a year,” Dreese said.

Dreese said he understands why some young athletes specialize, but he doesn’t recommend it. Chronic overuse injuries account for about half of new injuries in pediatric sports medicine practices, according to the International Youth Conditioning Association.

Children who specialize can develop Osgood Schlatter’s Syndrome — which causes knee pain — and os calcis apophysitis — which causes heel pain.

In adolescents and young adults, there’s a risk of shin splints, and patellofemoral syndrome, also known as “runner’s knee.”

By playing a multitude of sports, kids are more likely to develop better coordination and muscle balance, doctors said.

Stankovich warned that kids who specialize face psychological risks. They begin to look at their sport more like a job and run the risk of burnout.

“It doesn’t take a doctor or an expert to tell you that when sports become so intense that they’re day in, day out, it’s not going to be as much fun for most kids,” Stankovich said. “There’s an apex that a person hits when they’re performing a skill. You hit a point where it’s no longer productive to put that kind of time and energy in it.”

Most parents aren’t tuned in to looking for signs of burnout, Stankovich said, which includes loss of intrinsic motivation to play the sport, difficulty sleeping, irritability and lethargy. Instead, parents become intoxicated with their child’s success.

“When you see kids who are not enjoying it anymore, but mom and dad are still foot on the accelerator ... then maybe (the child) bottles that all up,” Stankovich said. “At some point ... with all that cumulative stress, that’s where they either explode and engage in drinking, drug use, reckless behavior.”

Burnout itself can also lead to injuries. If a kid is mentally tuned out, they can lose their focus on the field or court.