Functional Shoulder Adaptations and Attack Form in High School Volleyball Players: Sex Differences in Range of Motion, Strength, and Dynamic Stability

Background: Shoulder function asymmetries are common in adolescent volleyball players, yet evidence beyond glenohumeral range of motion (ROM) is limited, and few studies jointly examine sex and attack form. Hypothesis: Shoulder asymmetries would differ by attack form, with bow-and-arrow hitters showing greater dominant-nondominant internal rotation (IR) strength and dynamic-stability asymmetry than straight-arm hitters. Second, we expected typical dominant-arm ROM and strength adaptations and greater strength and stability in boys than girls. Study Design: Cross-sectional study. Level of Evidence: Level 3. Methods: We evaluated 108 high school volleyball players (49 boys, 59 girls). Bilateral shoulder ROM, isometric strength, joint position sense, acromiohumeral distance, and dynamic stability (upper quarter Y-balance test [UQYBT]) were assessed. Asymmetry was defined as dominant minus nondominant. Exploratory logistic regression examined associations between attack form (straight vs bow-and-arrow/circular) and shoulder asymmetry, with an additional exploratory female-only subgroup analysis. Results: Both sexes showed marked dominant-side adaptations: reduced IR ROM (boys −20.3°, girls −17.6°; both P < 0.001) and increased external rotation (ER) ROM (boys 11.7°, girls 7.7°; both P < 0.001), with decreased total rotational motion. Boys had higher normalized IR and ER strength ( P < 0.001) and superior UQYBT performance ( P < 0.001), except inferolateral. In exploratory logistic regression, greater IR strength asymmetry (odds ratio [OR], 1.18; 95% CI, 1.01-1.40; P = 0.04) and smaller inferolateral reach asymmetry (OR, 0.92; 95% CI, 0.86-0.98; P = 0.01) were associated with using a bow-and-arrow/circular swing; however, no significant attack-form differences were observed in the exploratory female-only subgroup analysis. Conclusion: Characteristic overhead-shoulder profiles - IR loss, ER gain, and preserved ER/IR ratios - are already present in high school volleyball players. Associations between attack form and shoulder asymmetry should be interpreted cautiously and considered exploratory. Clinical Relevance: Clinicians may monitor IR ROM, strength balance, and upper-quarter stability to characterize shoulder function in adolescent volleyball players and to identify extreme or symptomatic asymmetries that may warrant individualized conditioning.