Potential injury mechanisms in ulnar collateral ligament injuries; magnitude and variability of elbow load in repetitive baseball pitching

A common overuse injury in baseball pitching is the Ulnar Collateral Ligament (UCL) injury, due to high and repetitive loading of the medial side of the elbow. This repetitive loading (i.e. external valgus torque), caused by pitching a high number of balls in a practice session or during a game, is resisted by the UCL and counteracted by the elbow muscles. The elbow muscles have the potential to shield the UCL from the full external load and were active in all fifteen participants during pitching. To understand the injury mechanisms, we investigated the effect of repetitive pitching on the elbow load magnitude and variability. In addition, we explored whether repetitive pitching affects elbow muscle activation during pitching. On a group level, the linear mixed models showed no significant associations of repetitive pitching with valgus torque magnitude and variability and elbow muscle activity. Significant large differences exist between pitchers in their individual courses in elbow valgus torque and muscle activity with repetitive pitching. This shows the importance of individuality in relation to repetitive pitching. To arrive at effective elbow injury prevention in baseball pitching, individual characteristics of changes in elbow load and muscle activity in relation to the development of UCL injuries should be investigated.