Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

Summary

We present a protocol to assess changes in neuromuscular function. Percutaneous electrical nerve stimulation is a non-invasive method that evokes muscular responses. Electrophysiological and mechanical properties of these responses permit the evaluation of neuromuscular function from brain to muscle (supra-spinal, spinal and peripheral levels).

Abstract

Percutaneous electrical nerve stimulation is a non-invasive method commonly used to evaluate neuromuscular function from brain to muscle (supra-spinal, spinal and peripheral levels). The present protocol describes how this method can be used to stimulate the posterior tibial nerve that activates plantar flexor muscles. Percutaneous electrical nerve stimulation consists of inducing an electrical stimulus to a motor nerve to evoke a muscular response. Direct (M-wave) and/or indirect (H-reflex) electrophysiological responses can be recorded at rest using surface electromyography. Mechanical (twitch torque) responses can be quantified with a force/torque ergometer. M-wave and twitch torque reflect neuromuscular transmission and excitation-contraction coupling, whereas H-reflex provides an index of spinal excitability. EMG activity and mechanical (superimposed twitch) responses can also be recorded during maximal voluntary contractions to evaluate voluntary activation level. Percutaneous nerve stimulation provides an assessment of neuromuscular function in humans, and is highly beneficial especially for studies evaluating neuromuscular plasticity following acute (fatigue) or chronic (training/detraining) exercise.

Introduction

Percutaneous electrical nerve stimulation is widely used to assess neuromuscular function¹. The basic principle consists of inducing an electrical stimulus to a peripheral motor nerve to evoke a muscular contraction. Mechanical (torque measurement) and electrophysiological (electromyographic activity) responses are simultaneously recorded. Torque, recorded at the considered joint, is assessed using an ergometer. The electromyographic (EMG) signal recorded using surface electrodes has been demonstrated to represent the activity of the muscle². This non-invasive method is not painful and more easily implemented than intramuscular recordings. Both m....

Protocol

The experimental procedures outlined received Institutional ethical approval and are in accordance with the Declaration of Helsinki. Data were collected from a representative participant who was aware of the procedures and gave his written informed consent.

1. Instrument Preparation

1. Clean the skin at the electrode location by shaving, and remove the dirt with alcohol to obtain low impedance (<5 kΩ).
2. Place two AgCl surface electrodes (recording diameter of 10 mm) at 2/3 of the line between the medial condylis of the femur to the medial malleolus for the soleus muscle; on the most prominent bulge of the muscle for the me....

Results

Increasing stimulus intensity leads to a different evolution of response amplitudes between H- and M-waves. At rest, the H-reflex reaches a maximum value before being totally absent from EMG signal, while M wave progressively increases until reaching a plateau at maximal intensity (see Figure 4 for a graphical depiction of the M-wave and Figure 6 for the evolution of M-waves and H-reflex with intensity). For the soleus muscle, the latency between the stimulus onset and M-wave is about 10.......

Discussion

Percutaneous nerve stimulation enables the quantification of numerous characteristics of the neuromuscular system not only to understand the fundamental control of neuromotor function in healthy humans, but also to be able to analyze acute or chronic adaptations through fatigue or training¹⁷. This is very beneficial especially for fatiguing protocols, where measurements must be performed as soon as possible after exercise end to avoid the effects of rapid recovery⁴².

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Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Biodex dynamometer	Biodex Medical System Inc., New York, USA		www.biodex.com
MP150 Data Acquisition System	Biopac Systems Inc., Goleta, USA
Acknowledge 4.1.0 software	Biopac Systems Inc., Goleta, USA		www.biopac.com
DS7A constant current high voltage stimulator	Digitimer, Hertfordshire, UK		www.digitimer.com
Silver chloride surface electrodes	Control Graphique Medical, Brie-Comte-Robert, France
Computer
1 Cable for connecting the Biodex to the MP150
1 Cable for connecting the Digitimer to the MP150
1 Cable for connecting the MP150 to the computer