Relationship between the shoulder, trunk, and pelvis kinematics during the deceleration phase of throwing

The shoulder motion during pitching is influenced by the trunk and pelvis motions, but their relationship during the deceleration phase of throwing on flat ground has not yet been clarified. This study aimed to investigate the relationship between shoulder, trunk, and pelvis kinematics at the maximum internal rotation (MIR) of the shoulder during the deceleration phase of throwing on flat ground.

The study participants included 17 male baseball players over 20 years old and at the recreational playing level. The recreational level was illustrated by players who did not practice at high intensity and had played only 1-2 competitions per week. Reflective markers were applied to the subject, and throwing motion was assessed using a three-dimensional motion capture system. Data were captured at 1000 Hz. We assessed the angle of the shoulder, spine, and pelvis at the MIR on flat ground. Internal shoulder rotation velocity and spinal and pelvic angular velocities were also assessed. The relationship between the shoulder, spine, and pelvis kinematics at the MIR was examined using simple linear regression analysis.

The internal shoulder rotation angle at the MIR was negatively associated with only the spinal flexion and rotation angle at the MIR (P = .006 and P = .010, respectively). No other significant associations between shoulder, spine, and pelvis kinematics were detected at the MIR.

For throwing on flat ground, the internal shoulder rotation motion may be suppressed by producing trunk flexion and rotation motion at the MIR.