Hand force is directly related to swimming velocity - the greater the force, the faster the velocity. This swimmer changes the angle of the left elbow too quickly. The rapid elbow flexion (from Position 1 to Position 2) causes the hand to move upward more than backward, resulting in a substantial loss of force. (The vertical lines on the graphs are synchronized with the video image.)

Position 1    Position 2

(Click the buttons to change the image.)

This force loss can be avoided by gradually changing the angle at the elbow. If the force loss is avoided, the average force will be greater and faster swimming will result.