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. 2018 Mar 20;6(3):2325967118760780.
doi: 10.1177/2325967118760780. eCollection 2018 Mar.

Role of Rotational Kinematics in Minimizing Elbow Varus Torques for Professional Versus High School Pitchers

Micheal J Luera  1 , Brittany Dowling  2 , Mitchel A Magrini  1 , Tyler W D Muddle  1 , Ryan J Colquhoun  1 , Nathaniel D M Jenkins  1
Affiliations

Role of Rotational Kinematics in Minimizing Elbow Varus Torques for Professional Versus High School Pitchers

Micheal J Luera et al. Orthop J Sports Med. .

Abstract

Background: Elbow injury rates among baseball pitchers are rapidly rising. However, this increase has been most dramatic among high school (HS) pitchers.

Purpose: To examine pitch velocity and the kinetic and kinematic characteristics of HS versus professional (PRO) pitchers to identify potential differences that may play a role in the increased risk of ulnar collateral ligament injury in youth pitchers.

Study design: Controlled laboratory study.

Methods: A total of 37 HS (mean ± SD: age, 16 ± 1 years) and 40 PRO (age, 21 ± 2 years) baseball pitchers completed maximal-effort baseball pitches during a single testing session, from which pitch velocity (PV), absolute and normalized elbow varus torque (EVTA and EVTN, respectively) during arm cocking and at maximum shoulder external rotation (MER), and 8 other elbow and shoulder torques or forces and rotational kinematics of the pelvis and trunk were analyzed, recorded, and compared.

Results: PV was greater in PRO than HS athletes; EVTA was greater in PRO than HS athletes during arm cocking and at MER; but EVTN was similar during arm cocking and greater in HS than PRO athletes at MER. In PRO athletes, PV was not related to EVTA during arm cocking or MER (r = 0.01-0.05). Furthermore, in PRO athletes, EVTA during arm cocking and at MER were inversely related to upper trunk rotation at hand separation and foot contact and to pelvis rotation at elbow extension (r = -0.30 to -0.33). In contrast, in HS athletes, PV was strongly related to EVTA during arm cocking and MER (r = 0.76-0.77). Furthermore, in HS athletes, PV and EVTA during arm cocking and at MER were moderately or strongly related to the other elbow and shoulder torques and forces (r = 0.424-0.991), and EVTA was not related to upper trunk rotation or pelvis rotation throughout the throwing motion (r = -0.16 to 0.15).

Conclusion: The kinetic and rotational kinematic differences observed between PRO and HS pitchers in this study may help explain the greater performance of PRO pitchers while allowing them to minimize EVT during pitching. HS pitchers, however, do not appear to be as capable of utilizing the forces generated by rotation of their trunk and pelvis to aid in pitching, and those who throw the hardest generate the greatest forces at the shoulder and elbow. As a result, they experience higher EVTs relative to their body size, which may place them at an increased risk of injury.

Clinical relevance: HS pitchers throw harder primarily by generating larger forces in the arm and shoulder. Thus, owing to the relative physical immaturity of HS versus PRO pitchers, these factors may place them at an increased risk of injury. Coaches may first wish to focus on improving the rotational kinematics of HS pitchers rather than first focusing on achieving greater pitch velocities.

Keywords: baseball; biomechanics; motion analysis; pitch velocity; pitching.

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Conflict of interest statement

One or more of the authors has declared the following potential conflict of interest or source of funding: B.D. is employed by Motus Global, which provided advanced biomechanical analyses for all levels of athlete as a paid service. N.D.M.J. was paid to present at a GNC-sponsored symposium and received support for this manuscript by a grant from the National Strength and Conditioning Association Foundation.

Figures

Figure 1.
Figure 1.
Illustration of the ways in which pelvis and trunk kinematic data were calculated. (A) Lead and back hip rotation, (B) pelvis rotation, (C) pelvis flexion, (D) trunk rotation, (E) trunk lateral flexion, and (F) trunk flexion.
Figure 2.
Figure 2.
The directions of the force vectors at the (A) shoulder and (C) elbow and the anatomic terms of motion at the (B) shoulder and (D) elbow that were used for kinetic data processing.
Figure 3.
Figure 3.
Upper trunk rotation at maximum knee height (MKH), hand separation (HSP), elbow extension (EE), foot contact (FC), maximum shoulder external rotation (MER), ball release (BR), and maximum shoulder internal rotation (MIR) for professional (PRO) and high school (HS) pitchers. Values are presented as mean ± SE. *Significant main effect for group across all phases (PRO > HS; P < .05).
Figure 4.
Figure 4.
Pelvis rotation at maximum knee height (MKH), hand separation (HSP), elbow extension (EE), foot contact (FC), maximum shoulder external rotation (MER), ball release (BR), and maximum shoulder internal rotation (MIR) for professional (PRO) and high school (HS) pitchers. Values are presented as mean ± SE. *Significant difference between PRO and HS (PRO > HS; P < .05).
Figure 5.
Figure 5.
Back hip rotation at maximum knee height (MKH), hand separation (HSP), elbow extension (EE), foot contact (FC), maximum shoulder external rotation (MER), ball release (BR), and maximum shoulder internal rotation (MIR) for professional (PRO) and high school (HS) pitchers. Values are presented as mean ± SE. *Significant difference between PRO and HS (PRO > HS; P < .05).
See this image and copyright information in PMC

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