Pitcher arm pain is usually caused by underuse or overuse.
Underuse often takes the form of the arm not being strong enough for the rigors of the baseball season. Johnny hasn’t thrown in many months, Little League practice starts, and after only a week of practice Johnny is pitching. His arm is not strong enough to pitch and he inflames a growth plate in the elbow or shoulder. Bad. Always have Johnny do a preseason throwing program before the start of season. MLB has developed these age-specific preseason throwing guidelines:
Overuse often takes the form of: pitching too much in one day; pitching too much in one game; not enough days of rest between pitching days; and, throwing and pitching year round. MLB and the MLB Medical Advisory Committee have developed these age-specific pitching guidelines:
8 & Under - http://m.mlb.com/pitchsmart/pitching-guidelines-ages-8-and-under
9-12 - http://m.mlb.com/pitchsmart/pitching-guidelines-ages-9-to-12
13-14 - http://m.mlb.com/pitchsmart/pitching-guidelines-ages-13-to-14
15-18 - http://m.mlb.com/pitchsmart/pitching-guidelines-ages-15-to-18