An application of Chasles' theorem to describe the rotation axis of golf swing

Abstract

The purpose of this study was to propose a method for describing the rotational motion of the entire golf swing by two lines about which the trunk and the lower limbs rotate respectively, and to visualize individual differences in the rotation axes. Three-dimensional whole-body motion data of three male golfers were collected using an IMU motion capture system and a helical axis was computed for each body segment at each interval of frames. The weighted average of the helical axes of the head, upper trunk, and lower trunk segments was computed for each interval to represent the rotation axis of the trunk. Similarly, the weighted average was calculated for femur, leg, and foot segments to represent the rotation axis of the lower limbs. The mean values and standard deviations of the position and orientation of each rotation axis were computed over each of the two swing phases (backswing phase & downswing phase) and animated as cones in computer graphics. Comparisons of the rotation axes among the three golfers revealed that the position and the direction of the axes are unique to each player.