Simple quantification for mechanism of baseball pitching motion using IMUs

Abstract

The purpose of this study was to realize the induced speed analysis of the baseball pitching motion using inertial measurement units (IMUs). The upper limb with a ball was modelled as a linked three-rigid-segment system consisting of the hand with a ball, forearm and upper arm. The linear/angular motion of each segment was estimated using the angular velocity output of the IMUs. The dynamic contributions of the joint torque term, the motion-dependent term (MDT), the gravitational term, and the modeling error term to the generation of ball speed and valgus/varus axial torque at elbow were obtained through the equation of motion of the system. Furthermore, the generating factor of the MDT was considered using a recurrent formula derived from the equation of motion. The results of dynamic contribution analysis obtained from estimated motion data using the IMUs (estimated data) showed that 1)the MDT was the great contributor to the generation of ball speed prior to the ball release and, 2) the joint torque was the main contributor to the generation of valgus/varus axial torque at elbow during the pitching motion. These results show mostly good agreements with those obtained from the analysis of a motion-capture system.