Comparison of Shoulder Kinetics Across Two Delivery Styles in High School Baseball Pitchers

Abstract

When throwing from the stretch position in baseball, pitchers typically perform either the high leg kick (HLK) or slide step (SS). Unfortunately, no research has examined kinetic differences at the shoulder between the two deliveries. PURPOSE: To compare shoulder kinetics of the HLK and SS in high school baseball pitchers. METHODS: Electromagnetic sensors were attached to 12 pitchers before a series of fastballs were thrown. Kinematic data were collected at a rate of 1000 Hz. Standard inverse dynamics were used to calculate throwing kinetics from the fastest pitch passing through the strike-zone for each delivery style. Paired sample t tests were conducted at foot contact (FC), maximum shoulder external rotation (MER), release (BR), and maximum internal rotation (MIR) to identify mean differences. RESULTS: Of the 24 kinetic parameters, only the magnitude of internal shoulder rotation torque at MER was observed to be different. CONCLUSION: The high school pitchers experienced different rotational torques about the shoulder at MER when using the different deliveries. It has been found that shear stress during late arm-cocking due to opposing torques at different ends of the humerus leads to humeral retrotorsion. Results indicated that using the SS delivery may be detrimental to the shoulder due to an increased internal rotation torque at MER. Increased torque, coupled with the high angle of external rotation, may result in increased shear stresses being experienced by the humerus during the SS. As these sheer forces increase, high school pitchers may be at an increased risk of developing humeral retrotorsion.TABLE 1: Magnitude (mean + standard deviation) of selected shoulder kinetics at specific moments for both the HLK and SS deliveries.