Can Forward Dynamics Simulation with a Simple Model Represent Complex Rotations of the Torso with Torsion?

This study generates and analyzes human torso rotation and torsion unisng a simple model (TRM sim). As most injuries happen in the upper limb during pitching related to torso rotation and torsion, TRM sim is effective in baseball First, we designed TRM sim and generated the motion by forward dynamics. For validation, we measured three different human torso rotations with varying degrees of torsion. By aligning the peak values of input and their timings with human motions, TRM sim represented human motion, such as the relationship between torsion and the angular impulse of trunk muscle torque. These results suggest that TRM sim can represent torso rotation with different torsion levels. This study aims to generate torso rotations with various torsion to reduce upper limb load during pitching, with potential applications in designing intervention techniques.