Movement of bat during swing according to course in baseball batting

Abstract

The purpose of this study was to analyze how the bat moves in correspondence with the pitching course in the batting of baseball from the viewpoint of differential geometry. Three subjects made swings corresponding to the three courses of center, in and out, with the aim of the tee stand set to the waist height. In order to obtain three-dimensional coordinates of the reflective marker affixed to the bat tip and the grip end, the marker was tracked using a VICON system. After interpolating and smoothing the obtained three-dimensional coordinate values, the tangent vector, the principal normal vector, and the binormal vector were calculated, and then the curvature, the radius of curvature, the center of curvature, and the torsion were calculated. From the trajectory of the bat tip and the grip end, it was possible to observe the difference of the swing corresponding to the course, but in order to clarify local bat movements near the impact, the tangent vector was useful. In addition, the curvature, the radius of curvature and the torsion were also useful for analyzing the movement of bat from start to impact. The trajectory of the center of curvature, that is, the evolute showed the difference of the swing corresponding to the course, but further investigation in the future was necessary by increasing sample since the shape of the curve is complicated and its characteristics are difficult to clarify.