Research Publication: Multi-segment contributions to induced ball velocity in Collegiate baseball pitchers
Multi-segment contributions to induced ball velocity in Collegiate baseball pitchers
Aguinaldo, Nicholson, Alderink, Kepple
38th International Society of Biomechanics in Sport (ISBS) Conference July 20-24, 2020. Published by NMU Commons, 2020
The purpose of this study was to implement an induced acceleration analysis (IAA) to estimate the contributions of multi-segment motion to the forward velocity of the ball in collegiate baseball pitchers. Marker-based motion capture and ground reaction force data were collected from a sample of 17 pitchers throwing off an instrumented mound. Kinematic and kinetic data were extracted to drive the IAA model to calculate the muscular and non-muscular contributions to ball velocity. The shoulder joint torque and velocity-dependent torque collectively made up the largest contribution to the total induced velocity of the ball at 61% and 37%, respectively. The model underestimated ball speed by 16%, owing to limitations in distal segment definitions. Although this IAA showed that the proximal segments make a small, direct contribution to forward ball velocity, decomposition of the velocity-dependent torque could further clarify the extent to which the legs, pelvis, and trunk indirectly contributes to ball velocity.
INTRODUCTION: Baseball pitching performance is typically evaluated by ball velocity, which is determined by movements produced by muscle and joint actions throughout the body. In an open kinetic chain such as overhand throwing, the velocity of the throwing arm is affected by the flow of energy through the chain via coordination of proximal-to-distal segmental motion, where muscular torques can induce accelerations of anatomically remote segments through dynamic coupling (Aguinaldo & Escamilla, 2020; Naito, Takagi, & Maruyama, 2011). However, decomposing the muscular and velocity-dependent (Coriolis, centripetal) components of segmental motion cannot be performed using conventional inverse dynamics approaches (Fregly & Zajac, 1996; Naito et al., 2011). One method used to understand the coupled dynamics of multi-articular body motion is an induced acceleration analysis (IAA), which quantifies how muscular torques cause accelerations of both adjacent and non-adjacent segments in the kinetic chain (Kepple, 2011; Zajac, Neptune, & Kautz, 2002). Previous IAA studies have shown that during overarm throwing, the cumulative effect of velocity-dependent torques strongly contributes to the rapid angular velocity of the throwing arm (Hirashima et al., 2008; Naito et al., 2017). Likewise, Alderink et al. (2008) extended an IAA by integrating the acceleration curves to determine how muscular and non-muscular torques contribute to the forward velocity of the baseball. Their study showed that the shoulder joint and velocity dependent torques comprised most of the total contribution to the induced velocity of the ball. However, their IAA was limited to data from six high school pitchers who threw on force platforms embedded on flat ground. It is unclear how muscular and non-muscular actions contribute to ball velocity in adult pitchers throwing off a baseball mound, which involves differences in kinematics and kinetics to those of flat-ground throwing (Slenker et al., 2014). Therefore, the purpose of this study was to use IAA to examine how muscular torques, gravity, and velocity-dependent effects contribute to the forward velocity of a ball pitched off an instrumented mound in collegiate baseball players.