Friday Brain Food

Friday Brain Food is a weekly feature of a research publication, with a summary and key findings provided. 

Werner SL, Jones DG, Guido JA, Brunet ME. Kinematics and kinetics of elite windmill softball pitching. The American Journal of Sports Medicine. 2006;34(4):597–603. doi:10.1177/0363546505281796

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Compared to baseball pitching, little information is available regarding shoulder stress during softball pitching despite time-loss injuries reported as a direct result of the pitching motion. Pitch counts, while popular in youth baseball, are not present in youth softball. The purpose of this study was to determine the relationship between kinematic (displacement, velocity, acceleration) variables and shoulder distraction force. The authors hypothesized that shoulder joint stress experienced by elite softball pitchers would be similar to those experienced by professional baseball pitchers. Additionally, the authors sought to compare joint forces obtained in the current study to previously reported data. During the 1996 Olympic Games, 24 pitchers volunteered to participate in the study. Researchers captured video from 3 high-speed cameras, placed in right and left field and behind and above home plate, during live game play. They then analyzed the highest velocity rise ball thrown for a strike from each participant; manually evaluating game film frame-by-frame to identify movement of anatomical landmarks during the delivery phase (top of backswing (TOB) → stride foot contact (SFC) → ball release (REL)). The table at the end summarizes key variables discussed in the results section. The variables with an asterisk (*) were correlated with shoulder compression force. The higher the value of shoulder compression force, the more distraction force the shoulder experienced. Professional baseball pitchers experience shoulder compression/distraction forces of 108 ± 16%BW, based on a similar study performed by the same lead author. High distraction loads at the shoulder are linked to labral tears and issues with the long-head of the biceps brachii. The authors propose that softball pitchers are also at risk, as shoulder compression/distraction forces in the current study were 80 ± 22%BW, with a range of 50%BW to 149%BW. They conclude with the recommendation that pitching mechanics should be honed to reduce shoulder compression/distraction force specific to the 7 variables correlated from their findings. Specifically, shoulder compression force would be decreased (reducing distraction force) with increased shoulder abduction at SFC and an increased stride angle. Shoulder compression force would be increased with landing in more knee flexion at SFC, higher degrees of shoulder flexion at SFC, a longer stride length, increased elbow flexion at REL, and a more open position of the hips at ball release.