In a time when increased regulation and better equipment have made youth sports safer than ever, a surprising type of injury is emerging from school gyms and playing fields in growing numbers: repetitive stress injuries.

 The causes, experts say, are year-round competition that leave little opportunity to rest overworked muscles and specialization that focuses on one joint or muscle group instead of exercising the whole body.

  Once virtually unheard of in young athletes, overuse injuries are now more prevalent among players young enough to play in Little League and Pee Wee football.

  A 16-year-old track and field star nursing runner's knee. A junior varsity pitcher suffering from tendinitis. A high school football player recovering from shin splints. A swimmer dealing with rotator cuff tendinitis and impingement. These are typical overuse injuries in popular sports, injuries that worry sports medical experts.

  So as school and park leagues' sports season kicks into high gear this fall, athletic trainers and orthopedists have this message for parents:

  "Kids have to rest, they have to be able to take a break," says Vinny Scavo, head athletic trainer for the University of Miami's Sports Medicine Health System. "They're playing so many games, in so many leagues, in so many tournaments, that it's gotten crazy. The body can only take so much."

  Organized sports for young people have never been more popular. The number of student-athletes in high school has grown from about 4 million participants in 1971-72 to more than 7 million last year. Recreational leagues have mirrored that growth, and some estimate that as many as 30 million young Americans participate in some kind of athletic activity.

  While the overall injury rate -- the number of injuries per young athlete per competition or practice -- has decreased for most sports, damage to the tendons, bones and joints that occurs over time because of repeated motions has become more commonplace.

  "We're seeing a lot -- a lot -- of overuse injuries," says Michele Benz, Palmetto High's athletic trainer. "Young athletes are playing year around, particularly here where there's good weather.

  "Instead of playing several sports and cross training that way, everybody specializes now. The prevention for (overuse injuries), of course, is obvious -- rest."

   Benz is not the only one reporting injuries once seen only in adults. A study revealed that "Tommy John'' surgeries, a technique used most notably on pitchers to replace a damaged elbow ligament, are more common now for younger patients. From 1991 to 1996, 12 percent of the surgeries were done on patients 18 and younger. By 2005, that number had increased to 30 percent. E. Lyle Cain, one of the researchers, attributes the increase to specialization and year-round playing.

EXTRA INNINGS

  Reasons abound for the increase in overuse injuries. Competition for both high school team rosters and college athletic scholarships has stiffened, prompting young athletes to play in several leagues at one time. It's not unusual for a top baseball player, for instance, to compete for both his high school team and a travel team. The same holds true in other sports, including soccer, lacrosse, basketball and softball.

 In addition, South Florida's weather allows certain outdoors sports leagues to field year-round teams;, a luxury cold weather climes to the north do not have. As a result, leagues have sprouted to meet the demand of parents and kids.

 "The day of the multi-sport athlete is over," declares Damian Huttenhoff, director of athletics and student support for Broward schools. "Years ago you had kids playing two or three sports and using different muscles. That just doesn't happen anymore."

 League commissioners and high school coaches are well aware of this trend and often impose or suggest limits to participation. Travel teams, for instance, keep a strict accounting of a player's pitch count. But a high school coach may not know that one of his athletes is also playing for an all-star or travel team.

  Coaches and trainers say it is in a team's best interest to help a player heal an injury. A star athlete riding the bench serves no purpose.

  Athletes themselves often don't realize they're getting themselves in trouble by doing too much. Three years ago Bryan Hesser, a pitcher for Coral Reef High in Miami, played for his school's freshman team as well as a travel team. Many of his friends were doing the same. When his elbow began to hurt, he didn't pay much attention. "I thought it would go away and I really didn't think there was anything serious," he remembers.

  But the pain got worse, and by May he could barely toss the ball. His parents took him to the doctor. Diagnosis: ligament strain. Had it gotten worse, he might have been a candidate for Tommy John surgery.

  "In hindsight," says mom Joanne, "I wouldn't have let him pitch and catch for the Khoury league. It was way too much. I would've reacted quicker, too. It wasn't his coaches that put him in that situation. It was our ignorance."

  Bryan, now a senior, went through a summer of rehab and was given lessons in stretching and proper throwing techniques. Though he plays year round, he doesn't play for a second league anymore. Nor does he catch, a position that aggravated his throwing arm. Perhaps more importantly, he and his parents "have grown very, very vigilant," says Joanne Hesser. "Everybody pretty much knows his pitch count." He has not had a problem since.

   Overuse injuries are often preventable. In addition to cutting back intensity and frequency of practice and play as Bryan Hesser did, medical experts suggest young athletes learn proper training and technique, paying close attention to warm-up exercises before participationand using ice afterward.

  If it hurts, stop.

  Yet athletic trainers say that children, eager to emulate the pros, often insist on returning to the field before their bodies are ready. They hide the pain or simply believe they're invincible.

CHEERLEADERS

  Samantha Benitez, 13, is one of those athletes. A veteran cheerleader, she admits that she often practices and competes in pain and doesn't tell her coaches or mother. In addition to fractures, she has endured plantar fasciitis, a painful inflammatory condition of the foot felt on the underside of the heel that probably was caused by too much tumbling -- an integral part of today's cheerleading routines.

  She describes the pain as ‘‘daggers in my feet." It was first diagnosed a couple of seasons ago and reappeared again in August, forcing her to wear Crocs, the only shoes that ease her walking.

 "I know it's a little crazy," admits Samantha. "But I really want to make the next level, so I do keep tumbling even if they tell me to stop."

  Mom Marsha Romero says she has been monitoring her daughter's progress since she was first diagnosed with the ailment. Samantha stayed away from tumbling for the entire summer and she does the special exercises the therapists recommend. "She pushes herself so much," Romero adds.

  "There's no glory in playing hurt," says Cheryl Golden, executive secretary of the Greater Miami Athletic Conference. "But they see it in the pros and they want to do the same. My line to coaches is, ‘If you wouldn't put your own child on the field in that shape, don't put someone else's child.' So many kids are under the impression that they absolutely need to play."

  Coaches say that sometimes it's the parents doing the pushing, urging their kids to return to the field long before they have had time to fully heal. "They want their kids getting playing time," says Dwayne Owens, athletic trainer at St. Thomas Aquinas in Fort Lauderdale. "Everybody wants the college scholarship."

  Performing year round puts extra stress on vulnerable body parts, such as ankles and knees. More exposure also increases an athlete's chances at suffering an acute injury from a fall or a collision.

 It happens in every sport. Competition has filtered down to cheerleading, where showing school spirit at pep rallies and on the sidelines is not enough. Private leagues that compete locally and nationally attract top female athletes who perform increasingly daring gymnastic stunts -- and the injury rate is proof.

 Cheerleading accounts for two-thirds of all sports-related deaths or serious injuries to high school girls. In fact, they suffered more catastrophic injuries than all other female school athletes combined -- about 65 percent of severe injuries on the high school level and 67 percent in college.

  Romero isn't surprised by the rate of injuries for cheerleading. A generation ago, when she cheered for a Tamiami club, it was all pom-poms and rah-rah. That's been replaced with such feats as the helicopter toss, where a cheerleader makes a 180-degree rotation after being thrown up in the air.

  "Now it's so much more physical," Romero adds. "These girls are real athletes. They do sit-ups, crunches, leg lifts, running. Most have gymnastics background or dance. It's very, very competitive."

  The National Federation of State High School Associations suggests high schools employ athletic trainers, who are on the front line in treating injuries as well as educating athletes in technique and prevention. Yet, while all Miami-Dade and Broward public high schools have trainers on their staff, only 25 percent of schools nationwide do; another 40 percent have access to one.

REC LEAGUES

   For all the fierce competition on the high school level, though, experts say the danger of injury is actually greater in recreational leagues, where there are no medical professionals readily available and most coaches are volunteers with little training.

   Miami-Dade and Broward schools, on the other hand, require physical exams and medical screenings of all their athletes. They also have emergency plans in place. Athletic trainers attend the "high impact'' sports events, such as football, soccer and wrestling matches, and are on campus during afternoon practices.

  In recreational leagues, "You're lucky if you have a mom who's a nurse on the sidelines," says Frederick O. Mueller, director for the National Center for Catastrophic Sport Injury Research, which keeps track of serious injuries and recently released the results of its cheerleaders study. "In most rec leagues, you have volunteer coaches who may or may not be qualified to deal with an emergency."