The Relationship Of The Kinematic Sequence And Shoulder Compression Forces During Fastpitch Softball

Abstract

INTRODUCTION: The Kinematic Sequence (KS) refers to the order of peak angular velocities of connected body segments during a specific movement. There are many possible KS patterns. The proximal-to-distal sequence (PDS) KS ordered: pelvis-> trunk-> arm-> forearm-> hand is reported as the most efficient pattern for overhead throwing. Simulation studies report that the PDS KS results in reduced torques across the joints of the overhead throwing limb, potentially reducing risk of injury. Another KS is the PDS Variant which has a similar PDS pattern of pelvis-> trunk-> arm->, but with simultaneous forearm & hand peak velocities. A third KS pattern, Delayed CORE, demonstrates delayed peak velocity of the trunk: pelvis-> hand -> trunk-> simultaneous arm & forearm. While the PDS KS concept is instructed in fastpitch softball pitching, KS studies have not been published. The study purpose was to investigate the KS in a group of fastpitch softball pitchers. METHODS: 3D biomechanical analyses using high-speed motion capture cameras (240Hz) were performed on 140 fastball pitches from 21 softball pitchers (16 high school, 5 collegiate, mean age 16.15 ± 2.31 y). For each fastball pitch, Visual 3D v6 biomechanical analysis software calculated the peak angular velocity of the pelvis, trunk, arm, forearm and hand after the time of stride which allowed KS identification. Shoulder compression forces and stride length was also calculated for each of 3 primary groups of fastball pitches PDS n =12, PDS Variant n= 28 and the Delayed CORE n= 27. ANOVA and T-test comparisons were performed. RESULTS: There were no significant differences in stride length between the 3 KS patterns, p = 0.14. The Delayed CORE KS pattern demonstrated statistically significantly greater shoulder compressive force than the other groups, mean= 8.23 ± 1.04 (F(2,64)= 23.45, p< 0.01). There were no differences in shoulder compression forces between the PDS (6.89BW ± 0.5) and the PDS Variant (6.74BW ± 0.73) group, p= 0.524. CONCLUSION: This foundational study is the first to apply a KS classification system to the fastball softball pitch. Use of the PDS or PDS Variant KS promoted less shoulder compression force than the Delayed CORE group. The KS classification system could potentially guide underhand pitching instruction for injury prevention.