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Graduation Term

2020

Degree Name

Master of Science (MS)

Department

School of Kinesiology and Recreation

Committee Chair

Adam E. Jagodinsky

Abstract

Background: Weighted baseball throwing programs are often used in the baseball practice, in an effort to increase pitching velocity. Joint torques and forces have been shown to be generally decreased with over-weighted baseball, while injury has been reported with the implementation of weighted throwing program. However, the possible injurious mechanism is not well understood in weighted baseball throwing.

Hypothesis: Throwing with increased ball weights will produce greater GH joint reaction forces, smaller GH torques, and decreased ball velocities.

Study Design: Controlled laboratory study.

Methods: 7 baseball pitchers (Age 15.7 ± 2.42) participated in the study. Participants performed 5 pitches for strikes with 5oz, 7oz, and 9oz baseballs. Full body, 3D segment position data were collected using a motion capture system (200 Hz). The highest velocities of 3 pitches for strike were selected and 3D marker trajectories input into a 19 DOF musculoskeletal model utilizing a standard inverse dynamics and static optimization routine to produce individual muscle forces to yield GH joint reaction forces. Compressive force, anterior shear force, and superior shear force on GH joint were calculated and compared with repeated measures ANOVA (alpha = 0.05) in peak values during entire pitching phase and mean values during acceleration phase. Bonferroni post-hoc tests were conducted for pairwise comparison when appropriate.

Results: Throwing heavier baseballs exhibited increased mean compression forces in the acceleration phase (5oz 1987 ± 472.5N, 7oz 2386 ± 544.1N, 9oz 2414 ± 601.1N, p < 0.01) and peak compression force during the pitch delivery (5oz 5514 ± 831.9N, 7oz 5941 ± 888.9N, 9oz 6097 ± 1070, p < 0.01). While significant difference was not found on anterior shear force and superior shear force, those shear forces were generally increased with heavier ball weights.

Conclusion: Weighted baseball throwing did not decrease GH joint forces even though smaller GH torques were observed.

Clinical Relevance: The over-weighted baseball throwing may not reduce stresses compared to the standard baseball.

Keywords: Baseball, Pitching, Glenohumeral joint reaction force, Weighted baseball

Access Type

Thesis-ISU Access Only

DOI

http://doi.org/10.30707/ETD2020.Sagawa.H

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