Electrical bioimpedance spectral markers distinguish balance ability in older adults without provoking fall risk

Balance assessment in older adults is central to fall-risk evaluation and rehabilitation planning, yet widely used clinical tests such as the single-leg stance require postures most likely to provoke a fall. A method capturing neuromuscular contributions to postural control during safer, static postures would meaningfully advance clinical and home-based assessment.

We investigated whether electrical bioimpedance (EBI) recorded over the extensor digitorum longus (EDL), a muscle contributing to fine ankle-level postural adjustments, carries spectral signatures reflecting balance ability without provocative testing. Twenty-eight community-dwelling adults aged 60 to 74 years were stratified into two balance-ability groups by single-leg-stance performance, and EBI was recorded using a tetrapolar configuration during sitting, stable standing, and tandem standing. After standardized preprocessing, signals were analyzed in the time and frequency domains using spectral and time-frequency decomposition with peak-band and transient-event detection. From 61 candidate features, a non-redundant primary set of 25 was retained through predefined reduction rules and correlation screening. Between-group differences were evaluated using activity-adjusted, feature-wise generalized estimating equations, validated by participant-level permutation testing, with multiple-comparison control across the retained feature set.

Physiologically meaningful spectral power was concentrated within 0-10 Hz across all three postures. After activity adjustment, two frequency-domain features remained significant under false discovery rate correction and one survived Bonferroni correction. Participants with better balance exhibited stronger oscillatory organization of the EBI signal, reflected in greater power concentration within identifiable spectral peaks and a greater peak count, whereas participants with poorer balance showed a less peak-dominated, more broadband profile with larger and more irregular low-frequency amplitude fluctuations.

Low-frequency spectral features of muscle EBI, recorded during safe static postures, distinguish balance ability in older adults and reveal differences in the temporal organization of distal postural-control activity. These findings support EBI-derived spectral markers as candidate muscle-level biomarkers of balance-control quality, offering a path toward safer, sensor-based assessment that does not require older adults to adopt postures associated with increased fall risk. The approach is well suited to integration with rehabilitation monitoring and could complement existing clinical balance evaluations in both supervised and unsupervised settings.