Mechanomyographic response during FES in healthy and paraplegic subjects

Mechanomyography (MMG) registers lateral oscillations of contracting muscles. Functional electrical stimulation (FES) improves the rehabilitation of paraplegic subjects and can be used in neuroprosthesis control. During FES application, muscular contraction responses may vary, possibly due to fatigue or adaptation of nerve cells face to electrical stimuli. This study measured the differences in MMG RMS and median frequency (MF) features between healthy (HV) and spinal cord injury (SCI) volunteers. Ten HV and three SCI participated in the research. FES waveform consisted of a monophasic square wave, 1kHz pulse frequency, 100us active pulse period and 3ms active burst period with burst frequency of 70Hz. For each stimulation series, three analysis windows were inspected. RMS and MF variations were inversely related. The obtained results may help to create new strategies of muscular closed-loop control.