Comparison of kinematic manipulability in baseball hitting at different hitting points

In baseball hitting, batters need to manipulate their bat positions based on the pitch location. To achieve this, batters must be capable of displacing the bat across a wide range of positions. However, no study has yet quantitatively evaluated this ability. Therefore, this study aims to assess the manipulability of bats when they hit a ball at different points using kinematic manipulability indices. The three-dimensional motions of 20 collegiate baseball players hitting stationary balls were recorded using a motion-capture system. Each participant's body was modeled as a system of 10 connected rigid bodies with 21 degrees of freedom, from which kinematic manipulability indices were calculated using measured joint angles and segment lengths. Statistical analysis revealed that, when hitting lower or more inside locations, the bat can be further displaced horizontally and across a wider range. By contrast, the vertical component of kinematic manipulability did not vary significantly across the hitting points, thus indicating that the batters' ability to manipulate the bat vertically might be relatively uniform regardless of the hitting location. The horizontal component was greater than the vertical component, thus suggesting that the batters are more capable of adjusting their bat position horizontally than vertically.