A Kinematic and Kinetic Comparison of Mound and Rocker Throws
Authors: Brady Anthony , Briend Sam , Caravan Alex , Lindley Kyle , O'Connell Michael E , Gowdey Griffin , Boddy Kyle J 
Published: February 2020

The stride phase of the baseball throwing motion is an influential aspect in throwing performance as described in previously published literature. The Rocker drill is a constraint that is often used to change or improve baseball throwing performance throughout a wide range of settings, coaches, and training programs. Due to the lack of quantified and documented effects of the Rocker drill on throwing mechanics, this study aims to identify the resulting changes in performance, kinematics, kinematic velocities, and kinetics from the Rocker drill and a variation of the Rocker drill to determine which constraint may promote more effective mechanical changes. We hypothesize that the normal Rocker drill will have significantly different throwing arm, trunk, and lower body kinematic positions at front Foot Plant, maximum throwing shoulder external rotation, and Ball Release, as well as significantly different ball velocity, maximum kinematic velocities, and throwing elbow kinetics when compared to the “Foot-up” variation of the Rocker drill. A total of 30 healthy baseball pitchers with collegiate or professional competition experience threw three to five regulation baseballs out of the “stretch” pitching position, the Rocker drill, and a less constrained, Foot-up variation of the Rocker drill as close to maximal intent as possible. Subjects wore retroreflective markers for use in kinematic measurements and ball velocity was measured with a Doppler radar device. Eleven statistically significant differences were found among the a priori tests conducted between the normal Rocker drill and the Foot-up Rocker drill. Ball velocity in the Foot-up Rocker was significantly greater than the normal Rocker (82.03 vs 79.53, p-value &lt; 0.0001).Within the trunk kinematics category, the normal Rocker drill showed significantly greater trunk rotation angle at both Ball Release (BR) (111.90 vs 108.43, p-value = 0.0008) and Maximum External Rotation (MER) (98.76 vs 95.85, p-value = 0.0220) while the Foot-up Rocker showed significantly greater trunk lateral tilt at both Ball Release (33.86 vs 31.66, p-value = 0.0021) and Foot Plant (FP) (5.55 vs -0.13, p-value = 0.0222) as well as trunk forward tilt at BR (21.25 vs 16.85, p-value &lt; 0.0001). Within the lower body kinematics category, the normal Rocker showed significantly greater front knee flexion at BR (41.71 vs 36.17, p-value = 0.0010), MER (49.51 vs 44.80, p-value = 0.0220) and FP (62.92 vs 51.04, p-value &lt; 0.0001) while the Foot-up Rocker had significantly greater pelvis rotation angle at FP (38.25 vs 26.51, p-value = 0.0432). Within the kinematic velocity category, the Foot-up Rocker had significantly greater shoulder internal rotation angular velocity (4295.33 vs 4143.25, p-value = 0.0006). This study aims to identify various mechanical and performance differences in the throwing motion between the Rocker drill and a less constrained, Foot-up variation of the Rocker drill. Ball velocity, trunk and lower body kinematics as well as kinematic velocities showed significant differences between the Rocker and the Foot-up variation of the drill. These results can be used by coaches and trainers to determine in which setting these drills may provide desired throwing motion adjustments.