In a 10-year study, young pitchers who threw more than 100 innings in any year were three and a half times more likely to suffer a serious shoulder or elbow injury than those who pitched fewer innings.
Young pitchers whose arms are less developed should be limited to even less, and no pitcher should continue to pitch when fatigued.
Based on these findings and their review of the literature, the study authors recommend that pitchers in high school or younger throw no more than 100 innings in competition in any calendar year. Young pitchers whose arms are less developed should be limited to even less, and no pitcher should continue to pitch when fatigued.
It has been known for years that too much pitching causes pain and injury and that young arms are particularly susceptible. But no one really knows how much pitching is too much. This study is a start towards answering that question.
The study only looked at serious injuries — injuries requiring elbow surgery, shoulder surgery or throwing injuries that caused retirement from baseball. The overall risk of such an injury during the 10 years of the study was 5%. For pitchers who threw more than 100 innings, this risk was 14% (4 of 29), while it was 4% for all other pitchers (20 of 452).
The authors suggest that a larger study, hopefully done over a broader geographical area, could shed more light on young pitchers' injuries. After all, the study recommendations are based on only four pitchers who threw over 100 innings and then got injured.
Another finding was that pitchers who also played catcher had a risk of injury more than double that of pitchers who did not catch. But this increased risk was not statistically significant because of the small number of total injuries in the study. A larger study could settle the question of whether or not this practice increases injuries.
The authors discourage young players from playing both pitcher and catcher. The reasoning is that the high number of throws a catcher makes back to a pitcher could compound the harm to an arm already fatigued from pitching.