The purpose of this study was to investigate influence of static and dynamic trunk alignment on shoulder kinematics in throwing. Sixteen healthy collage baseball players participated in this study. The subjects were instructed to perform two types of throwing attempts ; one was normal throwing as per usual, and the other was throwing with slouched posture by relaxing trunk muscles. Three-dimensional motion analysis was used for the static alignment and the two throwing motions. Correlations between the static trunk alignments and maximal shoulder angles during normal throwing were investigated. The shoulder angles were compared between the two types of throwing. The static trunk alignments were not significantly associated with the shoulder angles during normal throwing. Shoulder abduction angle during the throwing with the slouched posture was significantly smaller than that during the normal throwing from late cocking phase to acceleration phase (p＜0.05). The current finding indicates that decreased shoulder abduction angle (i. e. dropped elbow) may be caused by inadequate trunk posture in throwing. Therefore, it may be necessary to pay attention not only to shoulder but also to trunk posture during throwing for rehabilitation and prevention of the throwing injury of baseball players.
