Timing Of Peak Shoulder Distraction Force Between Pitch Types Across A Simulated Softball Game

Increased joint loading during softball pitching can place the upper extremity at risk of injury. Individual pitch types are associated with different magnitudes of joint loading, namely shoulder distraction force (SDF). The timing of peak SDF may be a factor in determining mechanisms of injury. PURPOSE: To determine changes in the timing and magnitudes of peak SDF in the fastball and change-up pitches across a simulated game. METHODS: Twenty softball pitchers (14.9 ± 1.8y [range: 11-18], 161.8 ± 20.0 cm, 75.9 ± 16.2 kg) with competitive experience throwing each pitch and active on a team roster participated. Participants pitched 4 innings of 25 randomly assigned pitches. Coordinate data were collected using an electromagnetic tracking system. Shoulder distraction force was obtained using inverse dynamics within biomechanical software and defined as a force longitudinal to the upper arm, directed away from the shoulder as a percentage of body weight (%BW). Timing of peak SDF was determined relative to pitch initiation (center of mass forward velocity > 1 m/s) measured as the sampling rate in seconds. Three pitches of each type from the first and last inning were analyzed. Two separate 2x2 repeated measures analysis of variance tests were performed to examine how inning and pitch type impacted the timing of peak SDF and the magnitude of peak SDF. RESULTS: There was a significant interaction between inning and pitch type (F1 59 = 5.17 p = .027). There were no differences in the first inning timing to peak SDF for pitch type. However, there was a significant difference for the last inning timing to peak SDF, where the fastball increased (M = .636 SD = .056 s) and the changeup decreased (M = .613 SD = .061 s). For magnitude of peak SDF, there were significant main effects for time (F1 59 = 4.20 p = .045) and pitch type (F1 59 = 81.25 p < .001). Peak SDF in the first inning (M = 70.0 SD = 11.5%BW) was higher than the last inning (M = 68.6 SD = 12.2%BW). Additionally, peak SDF for the fastball (M = 76.7 SD = 12.7%BW) was higher than the change-up (M = 61.9 SD = 13.8%BW). CONCLUSION: In the last inning of a simulated game, the timing of peak SDF was impacted differently for certain pitch types, although the magnitude of peak SDF decreased for each pitch. Conditioning shoulder musculature to experience peak forces at different times may aid against soft tissue injuries.