Sensorimotor Beta Power Modulation with Functional Electrical Stimulation to Enhance Reactive Balance Among People with Chronic Stroke—A Preliminary Study

Background: People with stroke (PwS) fall nearly twice as often as healthy counterparts, which may reflect deficits in reactive balance control. Those with greater motor impairment fall more often and tolerate lower perturbation intensities, so they may need supplemental agents within perturbation-based training. Our recent work showed that functional electrical stimulation (FES) during unpredicted stance slips immediately improved reactive balance biomechanics and reduced laboratory falls. Whether these peripheral and behavioral effects are accompanied by cortical changes remains unknown. Using mobile brain imaging via electroencephalography (EEG), we examined sensorimotor beta power during slips with and without FES. Methods: Nineteen participants (75.35 ± 12.62 years) with moderate-to-high motor impairment (Chedoke McMaster Leg ≤ 4/7) experienced two unpredicted stance slips in a randomized order: one with FES to the paretic quadriceps 50–500 ms after perturbation onset and one with sub-sensory sham stimulation (Sham-FES). Fifteen participants had artifact-free recordings. Primary outcomes were beta power in the 400 ms windows before and after perturbation onset. Secondary outcomes were laboratory falls and reactive stability; tertiary outcomes were compensatory step length, initiation time, and execution time. We compared conditions using McNemar and paired t-tests. Results: Pre-perturbation beta power was similar across conditions (p > 0.05). Beta power increased from the pre- to the post-perturbation window in both conditions (p < 0.01). Post-perturbation, PwS showed lower sensorimotor beta power during slips with FES than with Sham-FES (p < 0.05), accompanied by fewer laboratory falls, higher reactive stability, and shorter step initiation time. Conclusion: FES to the paretic quadriceps was accompanied by lower post-perturbation sensorimotor beta power and improved reactive balance control, with no pre-perturbation differences. These preliminary findings suggest a promising role for FES in reactive balance recovery among PwS and support further mechanistic study.