Cortical and neuromuscular features during a side-lying hip abduction drop task are associated with single-leg standing balance.

This study was conducted to examine cortical and neuromuscular features of anticipatory and compensatory postural control during a side-lying hip abduction drop task and their relationship with standing balance. Twenty-six healthy young adults performed a side-lying drop task, single-leg standing (SLS) and a lateral step-down test (LSDT). During the side-lying drop, electroencephalography, electromyography, and pelvic accelerometry were recorded, and indices for the anticipatory postural adjustment (APA) and compensatory postural adjustment (CPA) phases were calculated. Elastic net and correlation analyses were used to examine associations with standing balance outcomes. For SLS, relatively high variable importance with non-zero standardized regression coefficients was observed for CPA-phase internal oblique/transversus abdominis activity, APA-phase pelvic acceleration Root Mean Square, CPA-phase gluteus medius activity, the C3 N1 mean potential, and CPA-phase multifidus activity. In contrast, model performance for LSDT was poor, and no variable was considered a useful predictor. Correlations of corresponding postural control variables across tasks were not significant. These findings suggest that a side-lying drop task captures task-specific cortical and neuromuscular features related to static standing balance, particularly compensatory trunk and hip muscle activity, pelvic acceleration responses, and cortical processing reflected by the N1 component. This recumbent task may therefore serve as a simple probe of sensorimotor control relevant to balance, although its applicability to dynamic balance remains limited.