Biomechanical effects of sex and bat size on head-directed blunt strikes

Blunt force injury to the head frequently occurs in violent assaults. It is essential to understand how sex and bat size influence striking performance for forensic reconstruction and injury assessment. This study aims to determine how sex and bat size influence kinematic and spatial parameters during head-directed blunt strikes.

Thirty-six healthy adults (18 males and 18 females) performed strikes on a PVC dummy's head using two baseball bats. Three-dimensional motion capture system was used to obtain striking velocity, impact energy, upper-limb joint velocities, and spatial parameters. Two-way repeated-measures ANOVA was applied to evaluate the influence of sex and bat size.

Males exhibited higher striking velocity and energy using both bats, with 41.6% and 30.0% higher in velocity whereas 100.2% and 71.0% higher in energy. Higher striking energy was observed within both males and females when the long bat was used. Males showed significantly higher right shoulder velocity, elbow velocity, and wrist velocity. In addition, both males and females showed higher wrist velocity when using the short bat. Compared with males, females showed significantly larger offender azimuth angle (θ) and victim azimuth angle (φ). Moreover, θ increased for both males and females using the short bat. In addition, larger striking distance (L) were consistently observed for both males and females when using the long bat.

Males exhibited higher striking velocity and energy than females. Higher values in energy were observed when the long bat was used for each sex, suggesting a greater likelihood of severe injury. Differences in upper-limb kinematics and spatial parameters further reflected adaptations of sex and bat size. Collectively, these results provide quantitative biomechanical evidence that may support forensic reconstruction and analysis of offender-victim interactions.