Neuromuscular electrical stimulation: implications of the electrically evoked sensory volley

Abstract

Neuromuscular electrical stimulation (NMES) generates contractions by depolarising axons beneath the stimulating electrodes. The depolarisation of motor axons produces contractions by signals travelling from the stimulation location to the muscle (peripheral pathway), with no involvement of the central nervous system (CNS). The concomitant depolarisation of sensory axons sends a large volley into the CNS and this can contribute to contractions by signals travelling through the spinal cord (central pathway) which may have advantages when NMES is used to restore movement or reduce muscle atrophy. In addition, the electrically evoked sensory volley increases activity in CNS circuits that control movement and this can also enhance neuromuscular function after CNS damage. The first part of this review provides an overview of how peripheral and central pathways contribute to contractions evoked by NMES and describes how differences in NMES parameters affect the balance between transmission along these two pathways. The second part of this review describes how NMES location (i.e. over the nerve trunk or muscle belly) affects transmission along peripheral and central pathways and describes some implications for motor unit recruitment during NMES. The third part of this review summarises some of the effects that the electrically evoked sensory volley has on CNS circuits, and highlights the need to identify optimal stimulation parameters for eliciting plasticity in the CNS. A goal of this work is to identify the best way to utilize the electrically evoked sensory volley generated during NMES to exploit mechanisms inherent to the neuromuscular system and enhance neuromuscular function for rehabilitation.

Electrical stimulation for neuromuscular testing and training: state-of-the art and unresolved issues

“…In order to maximize the spatial recruitment during NMES, thus minimizing the extent of muscle fatigue, it has been recommended to implement different expedients during a treatment session such as progressive increase in current intensity, alteration in muscle length, and displacement of active electrodes (Maffiuletti 2010). In this cluster of articles, further approaches have been proposed to alleviate, at least in part, discomfort and other possible complications associated to the electrically evoked contractions (Botter et al 2011;Bergquist et al 2011;Gobbo et al 2011). Fig.…”

“…These two logical steps should necessarily precede all evidence-based applications of NMES directed toward the improvement of neuromuscular function in vivo. Within each column, studies are grouped by topic area, with the name of the first author presented in square brackets Bergquist et al (2011) provided an overview of how peripheral (direct activation of motor axon branches) and central (reflexive recruitment of spinal motor neurons by the electrically evoked afferent volley) pathways contribute to electrically evoked contractions and suggested that some of the limitations of NMES (particularly discomfort and random recruitment) could be minimized by increasing the contribution through central pathways. In fact, motor unit recruitment through central pathways may be more orderly, less synchronous and more spatially diffuse throughout the muscle, than recruitment through purely peripheral pathways.…”

“All talk no torque”– A novel set of metrics to quantify muscle fatigue through isometric dynamometry in Functional Electrical Stimulation (FES) muscle studies

“…The qualitative critique of various metric methods demonstrated for example, that although individual peak plots are indeed quite meaningful, their computation time is poor in relation to the other plots. Further, the extrema plots, with an average computational time, yield at best average meaningful data.In terms of experimental design, there were several avenues for optimisation, such as quantification of the exact site to provide optimal stimulation through use of a motor pen [27] and assessing whether to stimulate the femoral nerve or quadriceps directly as they differ in terms of aspects such as comfort [28]. Moreover, the lower limb and torso could be held still during the contraction process [29] to minimise the input of residual torques from other movements of the body.…”

The pulse duration of electrical stimulation influences H-reflexes but not corticospinal excitability for tibialis anterior

“…Neuromuscular electrical stimulation (NMES) involves the repetitive application of pulses of stimulation over a muscle belly or nerve trunk and can restore movement and reduce muscle atrophy for people who have had a spinal cord injury or stroke (Sheffler and Chae 2007;Bergquist et al 2011). NMES activates both efferent and afferent axons, resulting in muscle contractions and the transmission of an afferent volley to the central nervous system, respectively.…”