Body Roll and Handpath in Freestyle Swimming: A Computer Simulation Study

The purpose of this study was to determine the effect that body roll has on the path followed by the hand during the pull phase in freestyle swimming. The trunk and right arm were modeled as two rigid segments joined at the shoulder by a simple hinge joint. The arm segment was assigned an elbow flexion angle, and the hand was made to move in a plane through the shoulder parallel to the sagittal plane of the rotating trunk. Shoulder extension and trunk roll occurred simultaneously at selected rates. Medial deviations of the hand to the midline of the trunk can be obtained with body roll alone and require less roll than is usually observed among competitive swimmers. When body roll exceeds the amount necessary to produce the desired medial deviation of the hand, the swimmer must move the arm away from, rather than toward, the trunk's midline.