(12) BASEBALL BATTED BALL VELOCITY AND CONTRIBUTING VARIABLES FROM VERTICAL JUMP KINETIC AND KINEMATIC RELATIONSHIPS IN COLLEGIATE ATHLETES

Purpose: Relationships between baseball batted-ball velocity (BBV) and game batting performances such as batting average and slugging percentage have been previously reported, but it is not known if the factors contributing to jump test performances are also associated with BBV. This study examined the contributions of commonly assessed kinetic and kinematic variables from a counter-movement vertical jump test (CMVJ) to baseball exit velocities during a BBV assessment in collegiate student-athletes. Methods: Male collegiate baseball players (n=36; X±SD; hgt=181.7±6.8 cm, BW=85.9±9.6 kg) performed a BBV test to determine their maximal exit velocity when hitting off a tee. All subjects were currently competing in either NCAA D1 or NAIA collegiate teams. Each subject performed 10 swings and a calibrated radar (24.15 GHz tuning fork; Stalker Sport 2, Richardson, TX) determined ball velocities for each swing, from which the greatest ball velocity was used for subsequent statistical analyses. CMVJs with no arm swing were performed on a pair of 1-dimensional force plates (Hawkins Dynamics, Westbrook, ME) to determine numerous kinetic and kinematic CMVJ variables assessed at 1,000 Hz. A zero-order correlation matrix determined shared variances and based on these results and the subject sample size, three independent variables from the CMVJ test (unweighting phase duration [msec], mean braking power [W], positive net impulse [N·s]) were included in a forward-entry model multiple regression with BBV (mph) as the dependent variable (p< .05). Standardized beta coefficients were used to determine the % total variance for each independent variable included in the regression. Results: Peak BBV for all subjects was 91.6±5.6 mph. Two variables were included in the resulting multiple regression which significantly accounted for 44.6% of the total variance (adj. r²=.446, p< .001). Standardized beta coefficients indicated that mean braking power and unweighting phase duration accounted for 24.1% and 20.5% of the total variance, respectively. Conclusions: Since twelve CMVJ variables were significantly correlated with BBV (r≥.43; p< .01), this means that numerous CMVJ kinetic and kinematic variables were significantly associated with BBV. Due to the shared variances between independent variables, three were ultimately included in the multiple regression. The CMVJ variables that accounted for the explained variance represented the eccentric (unweighting) phase of the CMVJ. Greater CMVJ eccentric phase durations and greater magnitudes of braking phase power together accounted for the explained variance. Not included were variables related to increased lower limb stiffness and reactivity, or measures of propulsive performance. It appears that the ability to generate large eccentric mean power (and the contributing forces and velocities) during the unweighting and braking phases, as well as doing this in an appropriately long unweighting phase duration (but < 324 msec) are important for greater BBV. The 55.4% unexplained variance is reasonable due to the complex nature of the baseball swing. Practical Applications: These data suggest that CMVJ testing on a force plate can provide useful information about factors contributing to baseball batting performance, such as the ability to produce high levels of lower body eccentric power over an appropriate eccentric duration. Acknowledgements: This project was supported by the Clara Wu and Joseph Tsai Foundation.