Document Type

Senior Thesis

Publication Date

2-7-2014

Abstract

Ground reaction forces (GRFs) exerted on a pitcher in reaction to the push of their legs against the ground create torques about the center-of-mass (CM) and generate the angular momentum necessary to rotate the body, including the segments of the throwing arm. Thus examination of GRFs provides insight into the causal mechanisms responsible for segmental rotation in baseball pitching. PURPOSE: To determine the effects of delivery [wind-up (WU) vs. stretch (ST)] and pitch type [fastball (FB) vs. change-up (CU)] on GRFs in pitching. METHODS: Eight collegiate baseball pitchers (4 right-handed and 4 left-handed) provided voluntary informed consent and threw maximal effort FB and CU pitches from the WU and ST positions from a regulation indoor pitching mound. Five pitches of each type were thrown from each delivery position. Two Kistler (Model 9281B) force plates mounted rigidly to the floor and imbedded in the pitching mound recorded GRFs (1200 Hz) under the push-off and stride foot, respectively. A video camera (60 Hz) was used to estimate the instant of ball release and a radar gun (JUGS Pro- Sports Model; accuracy ± 0.25 m/s) recorded ball speed. Comparisons of the GRF variables were made using two-way repeated measures ANOVA. RESULTS: As expected, FB pitches had a higher ball speed relative to CU pitches (37.3±1.3 vs. 32.9+1.9 m/s, p<0.01); ball speed did not differ by delivery type. No pitch by delivery interactions were present. FB pitches had larger peak magnitude GRFs exerted in the anterior direction (direction of the pitch) on the push- off foot (FB: 0.78±0.13; CU: 0.75±0.14 BW; p<0.05) and exerted in the posterior direction on the stride foot (FB: -1.12±0.13; CU: -1.03±0.12 BW; p<0.01). WU pitches had larger mediolateral GRFs directed toward the throwing arm side exerted on the push-off foot (WU: 0.14±0.03; ST: 0.07±0.04 BW; p<0.01) and larger GRFs directed perpendicular to the surface of the mound (WU: 1.94±0.32; ST: 1.84±0.30 BW; p<0.05) exerted on the stride foot. CONCLUSIONS: FB pitches require greater anteriorly directed forces on the push leg to accelerate the pitcher forward and larger posteriorly directed forces on the stride leg to decrease the forward momentum of the pitcher. WU pitches involve a greater mediolateral range-of- motion of the CM and require larger mediolateral forces exerted on the push-off foot.

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