Energy Flow And Impulse Predictors Of Bat Speed During Baseball Tee Batting Using The Least Absolute Shrinkage And Selection Operator (LASSO) Regression

Abstract

Unlike baseball pitching, there currently is limited research on baseball batting to explain which biomechanical factors can best predict bat speed. Furthermore, an observational analysis has not been conducted to understand how ground reaction forces (GRF) and energy flow through the kinetic chain influence bat speed. PURPOSE: To understand how energy is generated, absorbed, and transferred through the kinetic chain and identify the best model of GRF and energy flow predictors of bat speed in the baseball swing. METHODS: Nine collegiate baseball players performed tee batting while their movements and GRF were recorded using a 3D motion capture system and two force platforms. Bat speed was recorded using an inertial measuring unit (IMU) sensor fixed to the knob of the bat. Biomechanical metrics were extracted from a total of 33 swings for energy flow and impulse analysis. A total of 27 energy flow and impulse discrete variables were inputted into a regression based on the LASSO regularization to determine the best model that predicts bat speed. Model performance was assessed using the root mean square error (RMSE) in units of m/s and an ordinary least squares (OLS) coefficient of determination. RESULTS: Players hit off the tee with a measured bat speed of 30.4 ± 1.3 m/s. The LASSO model predicted bat speed with a RMSE of 1.0 m/s (r2 = .597, p < .001) and included the back leg vertical impulse, lead leg propulsive impulse, lumbosacral (L5S1) energy absorption and transfer in the acceleration phase, and the lead hip energy absorption during follow-through. CONCLUSION: This study provides evidence that suggests that the key factors of determining bat speed during tee batting involve the momentum generated by the legs and the energy absorbed by the L5S1 and lead hip joints along with the energy transfer to and from the pelvis through these joints during the phases immediately before and after ball contact.