I see young athletes in my office every week that suffer from overuse injuries. Too much of a good thing can be harmful, especially when it comes to children playing sports. The way youth sports are organized these days, there are requirements that children specialize at a very young age. This results in repetitive movements in children that are skeletally immature which leads to overuse injuries. This is also caused by year around sports that leave little time for rest and recovery.
Over training with little rest can lead to a breakdown of the adolescent musculoskeletal system. Overuse leads to microtrauma from repetitive stresses without sufficient time to heal and undergo the natural healing process. The risk of overuse is more serious in young athletes because the skeletal system is still developing and cannot handle as much stress as mature bones. This can cause strains, sprains, stress fractures, etc., from over training. When they spend 9 months out of the year throwing a baseball, there arm is going to fatigue and fail unless there is time for adequate rest and recovery.
Muscle imbalance is another problem I see a lot in cross country runners. The repetitive running motion causes certain muscles to be well developed and others are very weak due to the lack of cross training. It is important for the kids to be involved in a variety of activities. This not only prevents their body from breaking down, but also prevents mental burn out. A variety of activities will allow the youth to prevent overuse injuries and allow them to enjoy their particular sport.