Differences in Glenohumeral Range of Motion, Shoulder Strength, and Humeral Torsion Between Right- and Left-handed High School Baseball Pitchers.

Background: Differences in shoulder range of motion (ROM), shoulder muscle strength, and humeral torsion between left- and right-handed high school baseball pitchers remain poorly characterized.

Hypothesis: Similar differences in shoulder ROM, strength, and humeral torsion between right-handed pitchers (RHPs) and left-handed pitchers (LHPs) observed in professionals will also be present in high school pitchers, with potential variations due to developmental stages.

Study design: Cross-sectional study; Level of evidence, 3.

Methods: The authors included 921 high school baseball pitchers (706 RHPs and 215 LHPs) and evaluated their age, height, weight, body mass index, baseball experience, shoulder ROM, and muscle strength. Humeral torsion was measured in 211 RHPs and 57 LHPs. The Mann-Whitney U test was performed to determine the differences between the RHPs and LHPs and between the dominant and nondominant sides in each group. Pearson correlation analysis was performed to test the relationship between humeral torsion and shoulder ROM. Logistic regression analysis was conducted to determine the independent factors associated with LHP.

Results: LHPs exhibited increased nondominant external rotation (ER) (103.1° vs 100.0°; P = .004), dominant horizontal adduction (HA) (23.0° vs 19.6°; P = .015), and side-to-side ratio in prone internal rotation (PIR) strength (107.6% vs 98.3%; P < .001) compared with RHPs. Additionally, LHPs were shorter (171.4 vs 172.9 cm; P = .002) with lower side-to-side differences in ER (5.7° vs 8.9°; P < .001) and HA (-6.5° vs -11.3°; P < .001), dominant prone ER (PER) strength (15.4 vs 16.8 kgf; P = .040), side-to-side ratio in PER strength (93.1% vs 103.7%; P < .001), and side-to-side differences in humeral torsion (5.8° vs 9.9°; P = .011) compared with RHPs. After adjusting for confounding factors, a smaller side-to-side ratio in PER strength (P < .001; OR, 0.911) and larger side-to-side ratio in PIR strength (P < .001; OR, 1.031) were independent factors associated with being an LHP.

Conclusion: LHPs have a decreased side-to-side ratio in PER strength and increased side-to-side ratio in PIR strength compared with RHPs. These findings suggest that shoulder-related biomechanical differences between right- and left-handed pitchers are evident in high school athletes.