Abstract
Background: While the kinematics of the pitching arm, trunk, and pelvis have been described and studied, glove arm kinematics remain an understudied portion of the pitching motion. Baseball pitchers seek to achieve maximum ball velocity in a fashion that does not place the arm at risk of injury.
Purpose: To assess the relationship between glove arm shoulder horizontal abduction and elbow flexion and pitching arm kinematics and kinetics among youth pitchers to determine whether recommendations can be made toward a safer pitching motion.
Study Design: Descriptive laboratory study.
Methods: Thirty-three right-handed youth male baseball pitchers (mean ± SD: age, 13.6 ± 2.0 years; height, 169.4 ± 14.3 cm; weight, 63.5 ± 13.0 kg; experience, 7.3 ± 3.0 years) threw 3 fastballs to a catcher while kinematic data were collected with an electromagnetic tracking system. The Spearman rank-order test was used to identify relationships between glove arm horizontal abduction and glove arm elbow flexion and various kinematics and kinetics found at maximum shoulder external rotation (MER) and ball release for the fastest fastball delivered by each participant.
Results: At MER, there were significant relationships found between a more flexed glove arm elbow and increased pitching arm elbow valgus force (rs[31] = −0.52, P = .002), increased pitching arm shoulder anterior force (rs = −0.39, P = .024), and decreased hip velocity (rs[31] = −0.45, P = .009). Additionally, there were significant relationships between greater glove arm horizontal abduction at MER and increased pitching arm humeral velocity (rs[31] = 0.52, P = .002) and increased trunk rotational velocity (rs[31] = 0.40, P = .022) at MER.
Conclusion: A more extended glove arm elbow and more horizontally abducted glove arm shoulder at MER could prove to be more advantageous for performance and possibly be a safer motion for the baseball thrower.
Clinical Relevance: The orthopaedic community can dictate safer biomechanics when communicating with pitchers, trainers, and pitching coaches.
Keywords: elbow injury; elbow valgus; kinematics; pitching
Introduction
Glove arm kinematics is an understudied portion of the pitching motion, and knowledge of the entire motion is important for performance improvement and injury prevention. Anecdotally, pitching instructors often recommend as a teaching point that pitchers pull the glove arm into the body. After examining the glove arm, Ishida and Hirano concluded that an unused glove arm restricts a pitcher’s trunk control, which limits its ability to twist. Pulling the glove arm into the body allows for the trunk to rotate, which may increase force generation through trunk rotation and decrease force generation through rotational torque generated by the shoulder, which has been associated with elbow injury in professional pitchers.
Factors affecting the timing and magnitude of trunk rotation should be of interest to baseball pitchers, coaches, and the orthopaedic community attempting to prevent injury. To increase ball velocity by controlling the moment of inertia of the trunk and upper extremity, the glove arm should be a point of focus. Because dynamic coupling takes place, a pitcher’s limbs should be oriented to maximize torso rotational velocity for momentum to be conserved and travel up the kinetic chain to the shoulder.
Conclusion
This study investigated and found associations between glove arm kinematics and kinetics/kinematics of the baseball fastball. An extended glove arm elbow and more horizontally abducted glove arm shoulder at MER is more advantageous to performance and may be a safer motion for the baseball pitcher.
Published in: The Orthopaedic Journal of Sports Medicine, 6(7), 2325967118784937. DOI: 10.1177/2325967118784937. © The Author(s) 2018.
Authors: Jeff W. Barfield, MS, CSCS; Adam W. Anz, MD; James R. Andrews, MD; Gretchen D. Oliver, PhD, FACSM, ATC, CES. Investigation performed at the Sports Medicine and Movement Laboratory, School of Kinesiology, Auburn University, Auburn, Alabama, USA.
