Muscle recruitment by intramuscular vs. nerve cuff electrical stimulation

Functionally useful reanimation of paralyzed limbs depends on achieving reliable fine-control of muscle recruitment and force. We have used force and EMG recordings and histochemical analysis to investigate the recruitment properties of intramuscular (IM) and nerve cuff (NC) electrodes implanted acutely or chronically in cat hindlimbs, focusing an stimulation intensities and frequencies of interest for functional electrical stimulation (FES). NC stimulation produced very steep and surprisingly unstable recruitment, mostly of the fast-fatiguable (FF) motor units (MUs). IM stimulation produced more gradual, reliable and less fatigable recruitment of a mix of MUs that tended to be localized in neuromuscular compartments.