BACKGROUND: Individual constraints such as fatigue may gradually influence a performer’s movement patterns over time. The degree of linkage between joint angles of the throwing arm can help describe the extent that joint actions are coupled. The purpose of this study was to examine changes in joint coupling patterns in softball pitchers at increased pitch counts. METHODS: Eighteen high-school softball pitchers (15±1.6y,1.6±0.2m,77.2±17.0kg) pitched four blocks of twenty-five randomly assigned common pitch types. Randomly determined rest ranging from four to seven minutes was provided between blocks to mimic time between innings of a game. Participants’ kinematics were captured using an electromagnetic tracking system which recorded positional data of sensors placed on body segments. Trials were trimmed from top of the pitch to end of follow through and interpolated 0-100% of the pitch. Each participant’s mean time series data of shoulder, elbow, and wrist sagittal-plane angular motion were determined from three fastball pitches in the first and last blocks. Joint-to-joint time series correlations were performed on the shoulder and elbow, shoulder and wrist, and elbow and wrist. To evaluate if the joint-to-joint correlation coefficients between the first and last blocks were statistically different, correlation coefficients were transformed into Z-scores and compared using Steiger’s Z-tests. RESULTS: The respective correlation coefficients for the first and last blocks were as follows: shoulder-elbow=.44/.34; shoulder-wrist=.68/.61; and elbow-wrist=.32/.25. The strengths and direction of the correlation coefficients ranged from weak to strong and were positive but non-significant (>.05). Differences in joint-to-joint correlation coefficients between the first and last blocks were non-significant: shoulder-elbow; Z-diff=.35,p=.73; shoulder-wrist; Z-diff=.32,p=.75; elbow-wrist; Z-diff=.19,p=.85. CONCLUSIONS: Greater joint coupling (higher coefficient) may represent a strategy to limit motions and simplify the task, whereas a releasing of joint coupling may represent more independent components or movement exploration. This work suggests joint coupling occurs in softball pitching but changes may be minimal at this pitch volume (100 pitches). Additional work identifying the effects of individual constraints on softball pitching is needed to understand workload implications on movement patterns and injury risk.

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