Comparison of Shoulder and Elbow Biomechanical Characteristics in Left- and Right-Handed Youth Baseball Players

<b>Background/Objectives:</b> This study investigated biomechanical differences between right-handed (RHPs) and left-handed (LHPs) youth baseball players by analyzing shoulder and elbow range of motion (ROM), muscle strength, and humeral torsion. Side-to-side asymmetries were also examined to identify potential handedness-related adaptations. <b>Methods:</b> This cross-sectional study included 2008 youth baseball players (1829 RHPs and 179 LHPs) aged 9-13 years; female players were excluded because of their small number, and only male participants were analyzed. Shoulder and elbow ROM, muscle strength, and humeral torsion were evaluated, with humeral torsion data collected from 1024 measurements (946 RHPs, 78 LHPs). Group differences were analyzed using the Mann-Whitney U and Wilcoxon Signed-Rank tests. Logistic regression analysis identified independent factors associated with being an LHP, while Pearson correlation analyses explored the relationships between humeral torsion and external/internal rotation. <b>Results:</b> LHPs exhibited significantly larger nondominant shoulder external rotation (<i>p</i> < 0.001), dominant internal rotation (<i>p</i> = 0.003), dominant shoulder horizontal adduction (<i>p</i> = 0.007), dominant elbow flexion (<i>p</i> = 0.006), and side-to-side prone internal rotation strength ratio (<i>p</i> < 0.001). LHPs also showed smaller dominant shoulder external rotation (<i>p</i> = 0.012), nondominant shoulder internal rotation (<i>p</i> = 0.001), nondominant horizontal adduction (<i>p</i> = 0.037), dominant prone external rotation strength (<i>p</i> = 0.002), and humeral torsion (<i>p</i> = 0.031). Humeral torsion differences correlated with external rotation in LHPs (r = 0.236) and internal rotation in RHPs (r = -0.153). Predictors of left-handedness included lower dominant shoulder external rotation (OR = 0.937) and higher dominant elbow flexion (OR = 1.410). <b>Conclusions:</b> This study provides novel insights into the normal functional characteristics of LHPs, an area that has been relatively underexplored. These findings serve as a basis for future studies on risk assessment, injury prevention, and performance optimization in youth baseball players.