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. 2020 Mar 17:11:191.
doi: 10.3389/fneur.2020.00191. eCollection 2020.

A Preliminary Study of Effects of Channel Number and Location on the Repeatability of Motor Unit Number Index (MUNIX)

Farong Gao  1 , Yueying Cao  1 , Chuan Zhang  2 , Yingchun Zhang  2
Affiliations

A Preliminary Study of Effects of Channel Number and Location on the Repeatability of Motor Unit Number Index (MUNIX)

Farong Gao et al. Front Neurol. .

Abstract

Motor Unit Number Index (MUNIX) is a technique that provides a susceptive biomarker for monitoring innervation conditions in patients with neurodegenerative diseases. A satisfactory repeatability is essential for the interpretation of MUNIX results. This study aims to examine the effect of channel number and location on the repeatability of MUNIX. In this study, 128 channels of high-density surface electromyography (EMG) signals were recorded from the biceps brachii muscles of eight healthy participants, at 10, 20, 30, 40, 50, 60, 70, 80, and 100% of maximal voluntary contraction. The repeatability was defined by the coefficient of variation (CV) of MUNIX estimated from three experiment trials. Single-channel MUNIX (sMUNIX) was calculated on a channel-specific basis and a multi-channel MUNIX (mMUNIX) approach as the weighted average of multiple sMUNIX results. Results have shown (1) significantly improved repeatability with the proposed mMUNIX approach; (2) a higher variability of sMUNIX when the recording channel is positioned away from the innervation zone. Our results have demonstrated that (1) increasing the number of EMG channels and (2) placing recording channels close to the innervation zone (IZ) are effective methods to improve the repeatability of MUNIX. This study investigated two potential causes of MUNIX variations and provided novel perspectives to improve the repeatability, using high-density surface EMG. The mMUNIX technique proposed can serve as a promising tool for reliable neurodegeneration evaluation.

Keywords: channel number; high-density; innervation zone; motor unit number index; repeatability; surface electromyography.

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Figures

Figure 1
Figure 1
(A) placement of high-density surface EMG grids, (B) An example of EMG signals acquired at nine contraction levels from three trials, (C) Examples of SIP epoch selection at submaximal (60% MVC) and maximal (100% MVC) contractions, (D) Potential mapping from one representative CMAP recording.
Figure 2
Figure 2
IZ identification and examples of channel labeling based on its distance to IZ in three representative cases: (A) one IZ located between two neighboring bipolar channels, (B) one IZ located on one bipolar channel, and (C) two distinct IZs. The gray dots mark the location of EMG electrodes, the red bars mark the location of IZ detected. The black traces are representative bipolar signals during voluntary contraction. The red lines mark the propagation of IZ.
Figure 3
Figure 3
CMAP (Left), MUNIX (Middle), and CV (Right) mappings from two representative subjects.
See this image and copyright information in PMC

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