Purpose: The kinematic sequence (KS) during a baseball pitch provides insight into an athlete's ability to efficiently transfer energy and develop segmental velocities, to assess the quality of body segment position and control. Study purposes were 1) to introduce the four-category Kinematic Sequence Classification System and 2) to compare elbow and shoulder torques and shoulder distraction force across the KS categories performed during the fastball pitch.
Methods: Thirty baseball pitchers (20.0 ± 3.1 yr) underwent 3D biomechanical pitch analyses of 249 fastball pitches. Seventeen distinct KS patterns were identified and assigned into four categories: 1) The proximal-to-distal (PDS) group includes the KS closest to theoretical ideal order of the five body segments (pelvis → trunk → arm → forearm → hand). The other categories were defined based on the segment where the first out-of-sequence peak angular velocity occurred: 2) distal upper extremity (DUE), 3) proximal upper extremity, and 4) pelvis/trunk. Throwing limb shoulder distraction force and shoulder and elbow torques were calculated. Linear mixed model analyses compared variables across KS categories.
Results: Average elbow valgus torques differed significantly across all categories, P = 0.023, and were greater for the DUE (73.99 ± 20.84 N·m) than the PDS (61.35 ± 16.79 N·m), P = 0.006. Shoulder external rotation torques were significantly different, P = 0.033, across categories.
Conclusion: The PDS group demonstrated less mechanical stresses on the throwing shoulder and elbow but was observed in only 12% of pitches. The DUE group was the most common and generated the greatest elbow valgus and shoulder external rotation torques. The KS can inform coaches and sports medicine clinicians where the greatest torques are incurred by a pitcher. A KS classification system may serve as a screening tool or target pitching instruction for injury avoidance.
Copyright © 2020 by the American College of Sports Medicine.