Adaptations to perturbation-based balance training with tDCS

Perturbation-based balance training (PBT) is a promising approach for improving reactive balance skills, but the role of the primary motor cortex (M1) remains unclear. This study investigated the role of M1 in short-term PBT combined with transcranial direct current stimulation (tDCS). Thirty-four healthy participants completed a three-session PBT involving surface translations, with anodal, sham, or no-tDCS delivered centered over M1. Electromyography of the tibialis anterior and soleus muscles, along with center of mass (COM) kinematics, were analyzed across long-latency responses (LLR1/LLR2 (reactive phase) and LLR3 (voluntary phase)). Balance improved across all groups, indicated by enhanced COM displacements in backward perturbations and increased COM velocity in LLR3 in forward perturbations. Only the anodal tDCS group showed reduced COM velocity in LLR2 in forward perturbations, heightened LLR1 activity, and decreased onset latency in the tibialis anterior muscle. The different indices of improved performance in forward and backward perturbations likely stem from direction-specific limits of stability. In forward perturbations, reduced reactive COM velocity may reflect stimulation-related improvement, while increased voluntary velocity implies training-only effects. Our findings suggest that tDCS centered over M1 may improve postural recovery by modulating neuromuscular activity, consistent with a contribution of cortical-subcortical communication to reactive balance control.