Zhit: A Composite Score Of Power Is Associated With Exit Velocity In Baseball Hitters

In baseball, hitting relies upon the coordinated transfer of strength and power through the kinetic chain (e.g. lower body, core, and upper body), and batted ball velocity, commonly referred to as exit velocity (EV), is a key performance indicator. PURPOSE: The purpose of this study was to examine the associations of lower body strength and power, rotational power, and upper body power with EV. METHODS: Thirty-seven hitters (177.8 ± 6.2 cm, 85.9 ± 10.7 kg, 17.4 ± 5.6% body fat) from a NAIA collegiate baseball team participated in the study. Physical performance metrics were assessed as follows: Lower Body Strength (isometric mid-thigh pull, IMTP, kg), Lower Body Power (countermovement jump performed on force plate, Watts), Rotational Power (rotational medicine ball throw, m/s), and Upper Body Power (kneeling medicine ball throw for distance, m). Z-scores metrics were calculated for each of the physical performance measures and summed to create a composite score called zHit. EV (km.h-1) was determined using a radar gun from a batted ball off a tee. Pearson correlations were computed and statistical significance was set a p < 0.05. RESULTS: The average EV was 142.0 ± 10.2 km.h-1. The correlations (r) between the predictor variables and EV were all statistically significant (p < 0.05): Lower Body Strength (r = 0.26), Lower Body Power (r = 0.65), Rotational Power (r = 0.34), and Upper Body Power (r = 0.21). The zHit score calculated using Lower Body Strength, Rotational Power and Upper Body Power yielded a correlation of 0.46 with EV, while the correlation between EV and zHit score calculated using Lower Body Power, Rotational Power and Upper Body Power was 0.59. CONCLUSIONS: The findings indicate that common physical performance measures routinely conducted in strength and conditioning/applied sport science settings were significantly correlated with EV and the zHit score computed with lower body, rotational, and upper body power variables explained 32% of the variance in EV. Future studies should examine the relationship between the kinematic sequential lower extremity-trunk-upper extremity whole-body movements and rotational velocities using wearable technology sequencing data and EV compared to common physical performance measures.