Identifying coordination between joint movements during a throwing task with multiple degrees of freedom.

It is known that coordination between joint movements is crucial for the achievement of motor tasks and has been studied extensively. Especially, in sports biomechanics, researchers are interested in determining which joint movements are coordinated to achieve a motor task. However, this issue cannot be easily addressed with the methods employed in previous studies. Therefore, we aimed to propose a method for identifying joint coordination. Subsequently, we examined which joint movements were coordinated using accurate overhead throwing, which required reduction in vertical hand velocity variability. Fourteen baseball players participated by attempting throwing using a motion capture system. The index of coordination for each joint movement and the effect of deviation of one joint movement on vertical hand velocity were quantified. Our results showed that the shoulder internal/external rotation angle (θ) and the other joint movements or the shoulder horizontal flexion/extension angular velocity (ω) and the other joint movements were coordinated. These results could be explained by the fact that the effects of the deviation of the shoulder internal rotation angle (θ) and shoulder horizontal flexion angular velocity (ω) on vertical hand velocity were larger than those of the other joint movements. This meant that it was necessary to cancel the deviations of θ and ω by the other joint movements. These findings indicate that the method proposed in this study enables the identification of which joint movements are coordinated in multiple degrees of freedom.