Association Between Isometric Hip Muscle Strength and Y-Balance Test Performance in Healthy Adults

Background/Objectives: Dynamic balance during the Y-Balance Test (YBT) relies on coordinated multi-joint control of the lower extremity. Although hip muscle strength is considered important for YBT performance, the relative contribution of individual hip muscle groups remains insufficiently understood. This study aimed to examine the associations between isometric hip abduction, external rotation, and extension strength and YBT performance in healthy adults. Methods: In this cross-sectional study, 104 healthy adults underwent assessment of isometric hip abduction, external rotation, and extension strength using strap-stabilized handheld dynamometry. Hip extension strength was measured in the prone position with the knee flexed to 90°. Strength values were normalized and expressed as joint torque (Nm/kg). YBT performance was assessed in the anterior, posteromedial, and posterolateral directions and as a composite score. Associations were examined using Pearson correlation coefficients. To account for the dependency of bilateral measurements, a linear mixed model (LMM) was used to evaluate the collective and independent contribution of hip strength components to YBT performance, with sex, age, and BMI included as covariates. Results: All hip strength measures showed significant positive correlations with YBT performance (r = 0.19-0.49, p < 0.05). Hip extension strength demonstrated the strongest associations, particularly with posterolateral reach (r = 0.49). After adjustment for demographic covariates, sex was the strongest predictor of YBT performance across all directions (β = 7.8-8.9, p < 0.001), with males achieving higher scores than females. Hip extension and abduction strength were significant predictors of posterolateral reach (p < 0.05), whereas no hip strength variable independently predicted anterior reach or composite score after adjustment for demographic factors. No significant differences in YBT performance were observed between limbs. Conclusions: Sex was the strongest predictor of YBT performance in healthy adults. Hip extension and abduction strength were independently associated with posterolateral reach performance after controlling for demographic factors, suggesting that the association between hip muscle strength and dynamic balance may be direction-specific. These findings highlight the importance of accounting for sex when interpreting the relationship between hip strength and YBT performance.