Relationships between trunk rotation and arm swing in human walking.

In order to correlate the trunk rotation and arm swing with walking, the angular change of the horizontal rotation of the shoulder and pelvic girdle, and of the arm swing during one stride were recorded simultaneously in connection with the ground reaction force (GRF). The pelvic girdle rotated clockwise early in the left stance phase and then described a counter-clockwise rotation, while the shoulder girdle rotated in an opposite direction to the pelvic girdle. The shoulder girdle rotation, however, stopped transiently in accordance with the acceleration phase in the GRF. The maximum extension of the arm swing was coincident with the immobility period of the shoulder girdle. From above findings, it may be concluded that the arm swing is affected by the acceleration force of the contralateral through counter-rotation of the trunk, and that the stability of the upper body is maintained by stopping of the shoulder girdle rotation.