Previous research on baseball pitchers' wrists, elbows, and should joints contributes to our understanding of pitchers' control over delicate joint motion and ball release. However, limited research on forearm, wrist, and hand joints prevents full comprehension of the throwing mechanism. The present descriptive laboratory study quantifies angular performances of hand and wrist joints while pitching breaking balls, including fastballs, curveballs and sliders, among pitchers with different skill levels. Nineteen baseball pitchers performed required pitching tasks (10 from university and 9 from high school). A three-dimensional motion analysis system collected pitching motion data. The range of joint motion in the wrist and proximal interphalangeal (PIP) and metacarpophalangeal (MP) joints of the index and middle fingers were compared among fastballs, curveballs and sliders. Thirteen reflective markers were placed on selected anatomic landmarks of the wrist, middle and index fingers of the hand. Wrist flexion angle in the pitching acceleration phase was larger in fastballs (20.58. ±. 4.07°) and sliders (22.48. ±. 5.45°) than in curveballs (9.08. ±. 3.03°) ( p = .001). The flexion angle of the PIP joint was significantly larger in curveballs (38.5. ±. 3.8°) than in fastballs (30.3. ±. 4.8°) and sliders (30.2. ±. 4.5°) ( p= .004) of the middle finger. Abduction angle of MP joint on the middle finger was significantly larger in curveballs (15.4 ±. 3.6°) than in fastballs (8.9. ±. 1.2°) and sliders (6.9. ±. 2.9°) ( p= .001) of the middle finger, and the abduction angle of index finger was significantly larger in sliders (13.5 ±. 15.0°) than in fastballs (7.2 ±. 2.8°) ( p= .007). Hand and wrist motion and grip types affect the relative position between fingers and ball, which produces different types of baseball pitches. A larger extension angle of the wrist joint and the coordination of middle and index fingers are crucial when pitching a fastball. Abduction and flexion movement on the MP joint of the middle finger are important for a curveball. MP joint abduction and flexion movement of the index finger produce sliders. Understanding the control mechanism in a throwing hand can help improve training protocols in either injury prevention or performance improvement for baseball pitchers.
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