About 40 percent of all sports injuries happen to children and young adults. Nationally, nearly 4 million individuals under age 15 are injured each year while engaged in sports.

Yet there are few specialists dealing with the pediatric aspects of sports medicine. And few people recognize that the injuries sustained by an adult differ markedly from those suffered by a growing youngster.

Bicycling, football, baseball, basketball, roller skating and use of playground equipment account for 75 percent of all sports injuries to children. By far, the largest number are injured in bicycling accidents, which account for 1.2 million injuries.

Sixty percent of all sports injuries to children fall into these categories: sprains, strains, contusions, abrasions and lacerations. Less than 15 percent are fractures.

Still, the rate of injury to children participating in sports is actually the lowest of any age group. That rate, according to a special study by the Consumer Product Safety Commission, is less than 10 percent. Of those injured, less than 2 percent are hospitalized.

Children's injuries tend to be less severe because they are smaller and less force is involved when they fall. In addition, children's bones are resilient and flexible; the ligaments are more elastic and the joint surfaces, because they have a small blood supply, are capable of repairing themselves.

Injuries to the ends of major bones in children and young adults can cause major deformities. The ends of the bones are growth centers. Such injuries can cause growth to stop, partially or totally.

There are good reasons why you should seek a specialist in sports medicine to treat young children's sports injuries: children are physically and emotionally different from adults. Even outstanding physicians may be unfamiliar with some of the diagnoses and treatment of children's problems.

Parents often ask if their children should play sports. Among physical and mental health professionals, there is no question that a balanced athletic program is a positive factor for general physical and emotional development.

The question of whether a child is old enough to play sports is answered not by age, but size and maturity. Boys in junior high school range in size from 4 feet 6 and weigh from 75 to 200 pounds. The issue is whether a child will be physically mismatched. The greater the difference in height and weight, in contact sports, the higher the chance that a child will get injured--both physically and emotionally. Some organized sports take these factors into account and require participants to be both of a certain age and weight.

One way to tell the relative physical age and maturity of a child or a young adult is by a physical exam. There are characteristic physical changes that occur during adolescence. A second way is to X-ray the wrist and hand, which have 29 individual growth centers. The rate of development of these growth centers determines the relative skeletal age of an individual.

Children whose skeletal and physical patterns mature earlier will be more powerful and better able to compete.

The problem is how to counsel late maturers regarding athletic and sports skills. By the time they are 20, the late maturers will, in all likelihood, be tall and perhaps more skilled and stronger than early maturers. However, because of the genetic variance in their development pattern, they should not be mismatched, which would be to their physical and emotional detriment.