ABSTRACT
A mathematical model was developed [1] to evaluate the contribution of body roll to medial-lateral (vx) and vertical (vz) hand velocities in freestyle swimming. The right arm was modelled as two rigid segments joined at the elbow to enable flexion and extension. The arm was linked to a rigid trunk with a joint capable of shoulder extension and abduction/adduction.
Simulations were performed for pull times (tPUIX) from 0.7 s to 1.1 s and maximum body rolls (θMAX) from 50° to 70° with a straight arm, and with the elbow flexing through 90°. For a simulation involving elbow flexion (tPUIX = 0.7 s, θMAX = 60°), mean values for vx and vz were 1.86 m/s and 2.24 m/s respectively. These values were 24% and 22% less, respectively, than those obtained from an equivalent simulation performed with a straight arm. These reduced velocities were due to the elbow flexion: 1) reducing the hand’s radii of rotation, and 2) creating a hand velocity component which opposed that resulting from body roll.
It was concluded that body roll makes a substantial contribution to medial-lateral and vertical hand velocities in freestyle swimming and may therefore play an important role in the generation of propulsive lift forces.
