# Impacts of dry swing intervention on bat speed and attack angle: an analysis of core intervention factors

## TL;DR

This study examines how using bats of different weights during warm-up swings affects bat speed and attack angles in baseball players, focusing on core movement factors.

## Contribution

The study introduces a novel analysis of core kinematic factors influencing bat speed and attack angles during dry swings with weighted bats.

## Key findings

- Attack angles changed significantly in the normal-weight bat group for 12–14 year-olds and university players.
- Hip internal rotation and inclination angle were significant core kinematic indicators affecting swing performance.
- Weighted or reduced-weight bats should be avoided by adolescent athletes with shorter training terms for warm-up swings.

## Abstract

This study investigated the effects of dry swing intervention using differently weighted baseball bats on bat speed and attack angles during actual swing, simulating warm-up routines. Additionally, it explored core kinematic factors impacting subsequent bat speed and attack angles.

Sixty-nine baseball players were allocated by stratified randomization into three groups—normal-weight, weight, and reduced-weight—within their respective age categories. Bat swing kinematics were collected using BLAST, while bodily kinematics were captured with Rebocap sensors. Differences between pre- and post-tests were analyzed, and core intervention factors were identified with an XGBoost model and SHAP-based additive explanations.

No significant bat speed differences were found, but attack angles varied significantly in the normal-weight bat group for 12–14 year-olds (p = 0.027, ES = −0.315) and university players (p = 0.018, ES = 0.456). Core kinematic indicators included hip internal rotation (p = 0.007, ES = 0.990) and inclination angle (p = 0.023, ES = 0.184) showed significant differences, including and for the 12–14 age group using normal-weight bats, and hip external rotation (p = 0.045, ES = 1.619) for the 14–16 age group using weighted bats.

Post-test attack angles were impacted by intervention elevation and inclination angles, particularly for non-long-term bats. Adolescent athletes with shorter training term should avoid weight or reduced-weight bats for warm-up swings.