Motor unit number index (MUNIX) derivation from the relationship between the area and power of surface electromyogram: a computer simulation and clinical study.

Motor unit number index (MUNIX) derivation from the relationship between the area and power of surface electromyogram: a computer simulation and clinical study.

J Neural Eng. 2018 Feb 09;:

Authors: Miralles F

Abstract
Objetive. MUNIX is a technique based on surface electromyogram (sEMG) that is gaining acceptance as a method to monitoring motor neuron loss because is reliable and produces less discomfort than other electrodiagnostic techniques aimed to the same purpose. MUNIX assumes that the relationship between the area of sEMG obtained at increasing levels of muscle activation and the values of a variable called "Ideal case motor unit count" (ICMUC), defined as the product of the ratio between area and power of the M-wave by that of the sEMG, is described by a decreasing power function. Nevertheless, the reason of this comportment is not known. The objective of this work was to investigate if the definition of MUNIX could derive from more basic properties of sEMG.
APPROACH: The M-wave and sEMG epochs obtained at different levels of muscle activation from (1) the abductor pollicis brevis (APB) muscle of persons with and without a carpal tunnel syndrome (CTS) and (2) from a computer model of sEMG generation previously published were analyzed.
MAIN RESULTS: MUNIX reflects the power relationship existing between the area and power of sEMG. The exponent of this function was smaller in patients with a motor CTS than in the rest of subjects. The analysis of the relationship between the area and power of sEMG could aid in distinguishing a MUNIX reduction due to a motoneuron loss from that due to of a loss of muscle fibres.
SIGNIFICANCE: MUNIX is derived from the relationship between area and power of sEMG. This relationship change when there is a loss of motor units (MU), what partially explains the diagnostic sensibility of MUNIX. Although the reasons of this change are unknown, it could reflect an increase in the proportion of MU of great amplitude.

PMID: 29424359 [PubMed - as supplied by publisher]

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