The relationship between hip-shoulder separation angle and bat speed in division I batters.

Baseball hitting is a rotational movement that requires pelvis-trunk coordination to swing the bat with high velocity and accuracy. While hip-shoulder separation angle (HSSA) has been positively associated with golf club and baseball pitch velocities, its relationship with bat speed (BS) remains unclear. Therefore, the purpose of this study was to determine whether HSSA was associated with BS at the between- and within-batter levels. Markerless motion capture and ball tracking data were collected during NCAA Division I baseball games. The sample included 3958 swings from 247 batters. Maximum HSSA and maximum BS were collected, along with contact depth and pitch location. Contact depth was used as a covariate, and pitch location was used as an exclusionary criterion. Four two-level multilevel models were conducted. HSSA showed a small positive association with BS both between- and within-batter. Model 2 demonstrated that, within-batter, every 1° increase in HSSA above the batter's average was associated with a 0.05 m/s increase in BS. Between-batter, every 1° average increase in HSSA was associated with a 0.05 m/s increase in BS. Model 3 demonstrated that contact depth was positively associated with BS. Within-batter, every 1 cm increase in contact depth was associated with a 0.040 m/s increase in BS. Between-batter, every 1 cm average increase in contact depth was associated with a 0.036 m/s increase in BS. These findings suggest that HSSA is positively associated with BS during in-game baseball hitting, although the magnitude of this association may vary among individual batters.