Kinematic and Kinetic Predictors of Y-Balance Test Performance

BACKGROUND: The Y-Balance Test (YBT) assesses dynamic stability and neuromuscular control of the lower extremity. Several authors have analyzed kinematic predictors of YBT performance with conflicting results, but the influence of kinetic factors is not well understood. PURPOSE: To examine kinematic predictors of YBT performance and determine the joint kinetics which predict YBT performance. STUDY DESIGN: Cross-sectional study. METHODS: Thirty-one physically active individuals performed YBT trials on a force plate while whole body kinematics were recorded using a motion capture system. Sagittal, frontal, and transverse plane joint kinematics and joint moments were calculated at maximum reach in each YBT reach direction. Variables correlated with reach distances at the p < 0.2 level were entered into a stepwise linear regression. RESULTS: In the anterior direction, knee flexion and torso rotation (R(2)=0.458, p<0.001) and knee extensor and hip abductor moments (R(2)=0.461, p<0.001) were the best kinematic and kinetic predictors of reach distance. In the posterior medial direction, hip flexion, ankle dorsiflexion, and ankle rotation accounted for 45.8% of the variance in reach direction (p<0.001) while hip and knee extensor, and hip abductor moments explained 72.6% of the variance in reach distance (p<0.001). In the posterior lateral direction, hip flexion and pelvic rotation (R(2)=0.696, p<.001) and hip extensor moments (R(2)=0.433, p=0.001) were the best kinematic and kinetic predictors of reach distance. CONCLUSION: The ability to generate large hip and knee joint moments in the sagittal and frontal plane are critical for YBT performance. LEVEL OF EVIDENCE: 3.