Kinematic analysis of upper limb coordination during a multi-directional reaching task: specific examination of shoulder girdle movement.

[Purpose] This study was conducted to show the directional specificity of a reaching motion and to verify the three-joint coordination of the sternoclavicular joint, shoulder joint, and elbow joint. [Participants and Methods] The participants in this study were 10 healthy adult males. A reaching task for the upper limbs in a horizontal plane was assessed and measured. The trajectory, joint angle, and joint range of motion were calculated using a three-dimensional motion analyzer. [Results] The joint angle changes of the three joints were related in a circular radiation pattern. The sternoclavicular joint and shoulder joint were related in a fan-shaped radiation pattern. On the other hand, the sternoclavicular joint and elbow joint were related in a linear functional relation except for T3 and T8. [Conclusion] The results suggest that the coordinated motion of the shoulder joint and elbow joint controls the direction and extent of the motion track, while the coordinated motion of the sternoclavicular joint and elbow joint finely regulates the track. There also is a degree of difficulty in motion depending on the direction, which is apparently defined by a combination of joint motions.