Computational Study on Spatially Distributed Sequential Stimulation for Fatigue Resistant Neuromuscular Electrical Stimulation

Neuromuscular electrical stimulation (NMES) is used to artificially induce muscle contractions of paralyzed limbs in individuals with stroke or spinal cord injury, however, the therapeutic efficacy can be significantly limited by rapid fatiguing of the targeted muscle. A unique stimulation method, called spatially distributed sequential stimulation (SDSS), has been shown clinically to reduce fatiguing during FES, but further improvement is needed. The purpose of this study was to gain a better understanding of SDSS-induced neural activation in the human lower leg using a computational approach. We developed a realistic finite element model of the lower leg to investigate SDSS, by solving the electric field generated by SDSS and predicting neural activation. SDSS applied at 10 Hz was further compared with conventional transcutaneous stimulation that delivered electrical pulses at 40 Hz through a single electrode. We found that SDSS electrically activated multiple sub-populations of motor neurons within the TA muscle that fired at frequencies ranging between 10 Hz and 40 Hz. This complex nerve activation pattern depicts the mechanism of action of SDSS for reducing muscle fatigue during NMES.