Kinetic Factors Influencing Y-Balance Test Performance Kinetic Factors Influencing Y-Balance Test Performance

Abstract

The Y-Balance Test (YBT) is a movement screen which assesses dynamic stability and neuromuscular control of the lower extremity. Several studies have analyzed kinematic predictors of YBT performance, but kinetic factors determining YBT performance are not well understood. PURPOSE: To determine relationships between sagittal, frontal, and transverse plane joint kinetics and YBT performance. METHODS: 31 healthy individuals (15M, 16F; age 23.1 ± 7.3; height 172.3 ± 9.1 cm; mass 59.05 ± 9.8 kg) participated in this study. Whole body kinematics were recorded using a motion capture system while dominant limb YBT trials were performed on a single force plate. Joint moments were calculated using inverse dynamics. Maximum reach distances normalized to leg length in the anterior (A), posterior-medial (PM), and posterior-lateral (PL) directions were calculated. Joint moment values at maximum reach in each direction were determined. All joint kinetic variables which were correlated with max reach distances at the p < 0.1 level were entered into a stepwise linear regression. RESULTS: In the A direction, a model containing knee extensor moment explained 21% of the variance in reach distance (p = .01). In the PM direction, a model containing hip extensor and knee rotator moments explained 67% of the variance in reach distance (p < .001). In the PL direction, a model containing hip extensor moments explained 34% of the variance in reach distance (p=.001). CONCLUSIONS: Performance on the YBT is primarily influenced by the joint moments at the hip and knee. These results support previous claims that YBT performance is an indicator of neuromuscular control of the lower extremity, and at the hip and knee in particular. Further studies should evaluate the extent to which muscular strength influences both the moments generated during YBT and relationships between joint kinetics and YBT performance.Table 1:: Stepwise multivariable regression results for relationship between joint moments at peak reach direction and YBT performance.