Muscle-specific Cortical Adaptations To Balance Training With Electromyographic Biofeedback In Able-bodied Individuals

Abstract

The use of electromyography biofeedback (EMG-BF) is frequently incorporated among patients with neurological and musculoskeletal injury to restore neuromuscular function and improve real-time awareness of muscle function. Its effects on central nervous system function are not well documented in lower leg models, leaving its efficacy in certain populations unclear. PURPOSE: This study aimed to measure reflexive and cortical excitability before and after a balance training intervention with and without EMG-BF. METHODS: Nineteen healthy participants volunteered for this study (183.0±20.1cm; 69.0±13.1kg; 21.1±2.3yrs). Reflexive excitability was assessed using the Hoffmann reflex from the tibialis anterior (TA), peroneus longus (PL), and soleus (SOL) through peripheral stimulation of the sciatic nerve in the popliteal fossa to obtain Hmax:Mmax ratios. Cortical excitability was assessed via transcranial magnetic stimulation to quantify motor evoked potential (MEP) size at 110 percent of TA resting motor threshold. Neural excitability was measured before and after two 30-minute balance training sessions. The control group (n=9) performed only balance training while the experimental group (n=10) received balance training with EMG-BF to maintain 30 percent of maximal PL contraction. Differences before and after training across groups were assessed using factorial analysis of variance (α=0.05). RESULTS: No differences between groups were observed for reflexive excitability (F=0.00, p=0.96). No MEP size differences were observed for TA (F=0.63, p=0.45) or PL (F=0.53, p=0.48); but a significant time by group interaction was observed for SOL (F=4.315, p=0.044). EMG-BF decreased SOL MEP size after training (0.083%Mmax to 0.048%Mmax). CONCLUSIONS: EMG-BF with short-term balance training decreased cortical excitability to SOL compared to balance training alone, perhaps representing reciprocal inhibitory mechanisms to the postural plantarflexors. These findings may have implications when considering interventions for dystonic or spastic populations.