Relationship Between the Kinematics of the Trunk and Lower Extremity and Performance on the Y-Balance Test

Background: The lower quarter Y-balance test (YBT-LQ) has been recommended as a measure of dynamic postural control in the clinical setting; however, information about the relationship between performance on the YBT-LQ and joint kinematics is limited. Thus, the kinematic predictors responsible for performance on the YBT-LQ need to be identified for accurate evaluation of dynamic postural control. Objectives: To identify the kinematic predictors that best explain variance in performance on the YBT-LQ. Design: Cross-sectional design. Setting: University motion analysis laboratory. Participants: Thirty physically active participants. Methods: All participants performed the YBT-LQ. The kinematics of the trunk and lower extremity at maximal reach in each direction of the YBT-LQ were monitored using a 3-dimensional motion analysis system. Main Outcome Measurements: The correlations between reach distance and joint kinematics were assessed using Pearson's correlation coefficient, and the best predictors of performance on the YBT-LQ were determined using a stepwise multiple regression analysis. Results: Ankle dorsiflexion was the best single predictor of normalized reach in the anterior direction of the YBT-LQ (r(2) = 0.50), and the combination of ankle dorsiflexion and trunk extension explained 65% of the variance in the anterior normalized reach. Hip flexion was the best single predictor of posteromedial (r(2) = 0.60) and posterolateral (r(2) = 0.71) normalized reaches of the YBT-LQ. The combination of hip flexion and ipsilateral trunk bending and the combination of hip flexion and contralateral trunk bending accounted for 69% and 80% of the variance in the posteromedial and posterolateral normalized reaches of the YBT-LQ, respectively. Conclusions: These findings provide useful information on the relative contribution of joint kinematics to performance on the YBT-LQ when evaluating dynamic postural control.