The patient walked into the doctor's office, trying not to show the pain she felt with each step. She had torn the tissue at the growth line between her knee and shin; a bump had developed.

"The bump wasn't solid but fragments of loose bone," said Dr. Robert Nirschl, an orthopedic surgeon and medical director of the Virginia Sports Medicine Institute (VSMI). This condition -- Osgood-Schlaher's disease -- is usually seen in adults. Nirschl's patient was an 11-year-old soccer player. Nirschl operated and removed the fragments.

At another office, this one in Boston, a patient winced while taking off his jacket; excruciating pain stabbed his shoulder. An examination showed inflammation of the sac-shaped cavity filled with gluey fluids that lessen friction between the tendons and bony masses in the shoulder.

The diagnosis: bursitis, a common ailment of aging. But this patient was only 9.

"He is a competitive swimmer, and developed bursitis practicing three to four hours every day," said Dr. Lyle Micheli, director of the Sports Medicine Clinic at Boston's Children's Hospital.

Sports medicine physicians and clinics are seeing more children with acute and chronic adult diseases and injuries from sports, gymnastics and dance than in the past. It is not uncommon for children to suffer tendinitis, knee injuries, torn cartilage, and stress fractures of the spine, legs and long bones, as well as damage to shoulders, elbows and growth plates.

Why? Doctors cite such practices as repetitive training, and year-round training in a single sport, as well as pressure from coaches and parents to achieve perfection. The failure of many coaches to consider the child's natural physiology, strengths and genetic makeup also contributes to the injury rate.

"Many outstanding athletes have a genetic advantage," Nirschl said. "A good coach can see that early and develop those natural attributes. For other youngsters, all the training in the world will not make them Olympic team contenders. Coaches mustn't push children beyond their physical abilities and jeopardize growing bodies."

At VSMI, "we have teen-agers in weightlifting training coming in with arthritic spurs -- calcium buildup -- on their shoulders from repetitive training," said Janet Sobel, a registered physical therapist and director of rehabilitation at the institute.

Sobel sees an average of 30 new patients each month. With the baseball season starting soon, she expects VSMI will be treating more youngsters with "little league elbow," breakdown of the cartilage around the elbow. Surprisingly, youngsters playing the outfield rather than pitching usually develop it.

"The Herculean effort to nail a runner at the plate from the outfield can pull off the tissue at the growth line," Nirschl said.

Sports-related injuries and chronic medical conditions among young people are becoming a nationwide problem. Rigorous competition -- whether for an athletic scholarship, a spot on an Olympics or national team, or a shot at a professional sport -- drives many youngsters, their parents and coaches to relentless training.

At Boston Children's clinic, the number of patients has grown from 200 to 600 a month during the past three years. "Ninety percent of those patients are from organized sports," said Micheli.

"The over-achiever is a growing problem in children's sports medicine," said Dr. Paul Dyment of the Cleveland Clinic, chairman of the Sports Medicine Committee of the American Academy of Pediatrics. "Excessive training can lead to injury; yet if the youngster doesn't train to excel, he can't compete on a national and international level."

It is not uncommon for a gymnast to repeat a back flip 300 times until it is perfectly executed; however, that repeated action can cause stress factures of the spine or other bones. Dr. Bertram Zarins, chief of sports medicine of Massachusetts General Hospital, explained that children's joints are made of cartilage that develops into bone as they grow. The cartilage is weak, so repeated stress from the same activity can cause it to tear.

"A break occurs at the weakest point. Stress and pressure on the growth center or plate can cause permanent damage and deformity," said Zarins, an orthopedic surgeon and doctor to both the New England Patriots football team and the U.S. Winter Olympics team.

Physicians like Nirschl and Micheli would like to see certification and continuing education in sports medicine made requirements for coaches and dance teachers.

"In every sport there's good and bad technique," Nirschl said. "There's no reason coaches can't use good technique to promote good medicine. For example: in tennis, a technique that centers on the racket and its relationship to the ball can put pressure and strain the arm and shoulder. But coaches favor this method for immediate success. However, power is generated from the lower body and by shifting one's weight. This technique is better sports medicine. But it takes longer to excel and therefore is not popular."

Micheli added: "Some swimming coaches think increasing distance helps a swimmer excel. Instead, I'd like to see a focus on strengthening the athlete's muscles."

Nirschl recommends some of the protective training measures used by Gary Anderson, coach of the MARVA Tots and Teens gymnastics program for children 3 to 18 in the Rockville and Arlington areas. Anderson coached the 1983 U.S. gymnastics team to the Pan American games. There are some 1,500 children in his programs.

Anderson uses a gym with two sunken areas filled with soft foam-cushioned mats. The children use the sunken areas throughout training to prevent jarring damage or stress fractures while perfecting their routines. A sports medicine doctor and a therapist visit the MARVA training gym once a week to examine children and advise on what they can do to avoid injury.

Clinicians worry not only about acute injuries but also about chronic damage to youngsters' bodies. Knee injuries are a major concern. In gymnasts and ballet dancers, the emphasis on lean bodies leads some girls to develop anorexia nervosa -- self starvation. Many girls develop abnormal menstrual cycles.

Besides physical injury, coaches, parents and doctors need to be on the lookout for psychological damage that may affect youngsters in intensive sports training, said Micheli.

Laura White is a free-lance writer in Boston.