A survey of 203 healthy youth baseball players ranging from 8-18 years found that a large percentage had underlying baseline arm pain and fatigue. Only 26% reported that their arm never hurt when throwing. 20% indicated their arm never hurt the day after throwing. 30% of players reported that arm pain occasionally caused them to have less fun playing and 46% reported being encouraged, at least once, to keep playing despite having arm pain. Pitchers were more likely to report arm pain while throwing and the day after throwing and also to indicate that arm pain held them back from being a better player.
Source: American Journal of Sports Medicine, January, 2015