Role of Thigh Muscle Strength and Joint Kinematics in Dynamic Stability: Implications for Y-Balance Test Performance

Context: The Y-Balance Test Lower Quarter (YBT-LQ) is a widely utilized tool for evaluating dynamic postural control, requiring a combination of mobility and strength. This study aimed to investigate the combined relationship between isometric thigh muscle strength and joint kinematics on YBT-LQ performance. Design: Cross-sectional laboratory study. Methods: Isometric quadriceps and hamstrings strength were measured before the YBT-LQ in 39 healthy participants (27 females and 12 males). The test was performed under 3-dimensional markerless motion capture, where joint kinematics were extracted from the maximum reach position from each direction. Three multivariable linear regression models were then used to determine the strongest combination of predictors for YBT-LQ performance. Results: Greater hamstrings strength and increased knee flexion, ankle dorsiflexion, and trunk ipsilateral-flexion joint angles explained 56.8% (P < .001) of the variance in anterior reach. Hip flexion, knee flexion, and ankle dorsiflexion angles were the strongest predictors for posteromedial reach distance, explaining 73.0% of the variance (P < .001). Last, 43.3% (P < .001) of the variance in posterolateral reach distance was predicted by hamstring strength and knee-flexion angle. Conclusions: These results emphasize the importance of hamstring strength in YBT-LQ performance across different reach directions. Additionally, the kinematics illustrate a potential movement strategy for maximizing reach distance on the YBT-LQ in healthy individuals. Clinicians can utilize this information to guide interventions aimed at improving dynamic postural control, particularly by focusing on increasing hamstring strength and testing for impairments in specific movement patterns.