Correlation of absolute and relative limb differences in Y-balance test and asymmetry indices of CMJ, SJ and IMTP

Determine the relationship between Y-Balance Test (YBT) and force platform-based assessments, including squat jump (SJ), countermovement jump (CMJ), and isometric mid-thigh pull (IMTP), to evaluate lower limb stability and asymmetry.

Sixty-one recruited active professional firefighters were assessed for YBT absolute limb differences (anterior, posteromedial, and posterolateral directions) using the YBT classic formula or a force platform built-in formula, and for asymmetry indices of CMJ, SJ and IMTP derived from the force platform.

The absolute limb differences in YBT anterior (YBT-A) showed a moderate correlation (r > 0.4) with asymmetry indices of SJ concentric peak force (SJ-CPF), IMTP peak force component (IMTP-PFC), and IMTP peak force (IMTP-PF). Subsequently, limb relative differences for YBT-A were calculated using the built-in formula of the force platform, which also showed a moderate correlation (r > 0.4) with asymmetry indices of SJ-CPF, IMTP-PFC, and IMTP-PF. However, when considering either absolute or relative differences, YBT posteromedial asymmetry (YBT-PMA) or YBT posterolateral asymmetry (YBT-PLA) showed weak or negative correlations with asymmetry indices derived from the force platform.

This study demonstrated that YBT anterior asymmetry (YBT-AA) calculated by using either the YBT classic formula or the built-in formula of the force platform, showed a moderate correlation with asymmetry indices derived from the force platform. This study provides clinicians and researchers with different test methods for assessing lower limb stability.