Inter-joint Coordination Patterns and Their Variability in Baseball Pitching

Abstract

The number of throwing-related injuries remains high despite advancements in biomechanical studies over the past decades. Traditional biomechanical analysis relies on linear approaches, which analyze a single joint at a discrete time point. Furthermore, data are averaged across multiple trials, which does not account for the complex non-linearity of human movements. Therefore, the purpose of the studies was to incorporate a non-linear approach to understanding baseball pitching biomechanics. Study 1 investigated the effects of inter-joint coordination patterns on pitch metrics (pitch speed and the peak elbow varus torque). 60 collegiate pitchers were analyzed to evaluate inter-joint coordination by using pair-wise cosine similarity for each joint pair. The cosine similarity was stored in a long vector form to proceed with a clustering analysis. The clustering identified three clusters based on inter-joint coordination patterns. The clustering showed the difference in throwing arm coordination, especially in pronation/supination movement. There was no significant difference in pitching metrics between clusters. An exploratory analysis reveals that the biomechanical efficiency was different between clusters. Study 1 suggested that inter-joint coordination of the throwing arm may influence the biomechanical efficiency of the pitch. Study 2 investigated the variability of inter-joint coordination patterns at the trunk, shoulder, elbow, and wrist over the course of games. A total of 48 NCAA DI pitchers who pitched more than 50 pitches within games were included in this study. Kinematic data was collected at a baseball stadium during NCAA D I games by using a marker-less motion capture system. We used a vector coding technique to quantify the inter-joint coordination patterns by calculating the angle of the vector in an angle-angle plot. Furthermore, circular statistics were used to calculate the variability of the vectors by categorizing pitches into bins of 10 pitches. A statistical analysis revealed that inter-joint coordination patterns between the shoulder and elbow were constant, showing minimal changes in the variability throughout games. The result suggested that NCAA pitchers could generate a consistent movement pattern between the shoulder and the elbow during games. These findings can be used to evaluate the skill levels and readiness of pitches to return to games during rehabilitation.