Shoulder kinematics during pitching: comparing the slide step and traditional stretch deliveries

Although studies have investigated the traditional stretch delivery, there is little biomechanical data describing the slide step delivery in baseball pitchers. Thus, the purpose of this study was to compare shoulder kinematics across the traditional stretch and slide step deliveries. To collect kinematic data from thirty-seven high school baseball pitchers, electromagnetic sensors recording at 140 Hz were affixed to various body segments. The average of those data from the three fastest pitches passing through the strike-zone were analyzed for each delivery. At the instances of front foot contact and ball release, no differences were observed between the two deliveries. At the instant of maximum shoulder external rotation, differences were observed between the two deliveries with regard to plane of elevation (t(72)=4.19, p<.001), elevation (t(72)=-3.38, p<.001), and axial rotation (t(72)=2.49, p=.015). The mechanical differences observed between the two delivery styles may have the potential to impact both performance and injury. Also, based on these results there may be a tradeoff between injury risk and performance. Thus, further study is warranted in an effort to identify the interrelationships between injury risk, performance, and pitching kinematics when throwing from the stretch position.