Having been a lay coach for over 20 years, I have seen young athletes who have pushed their young bodies as if they were adults. This has an accumulating effect on the growing joints, ligaments, and muscle. Some is good and promotes growth, but when they push their bodies to excess damage occurs. Scar tissue forms, then shrinks but does not go away. Over time the athlete starts loosing flexibility, quickness and reaction time. You cannot medically treat a youth as you do an adult with cortisone and since our bodies heal faster when we are young, many injuries may seem to have healed, but in fact the scar tissue remains, building with each successive injury.