Three-dimensional amplitude characteristics of masseter motor units and representativeness of extracted motor unit samples

Publication date: Available online 19 January 2019

Source: Clinical Neurophysiology

Author(s): Bernd Georg Lapatki, Ulrike Eiglsperger, Hans Jürgen Schindler, Johanna Radeke, Ales Holobar, Johannes Petrus van Dijk

Abstract

Objective

This study aimed to characterize amplitude topographies for masseter motor units (MUs) three-dimensionally, and to assess whether high-density surface electromyography (HDsEMG) is able to detect MU samples that represent the masseter's entire MU pool.

Methods

Ten healthy adult volunteers participated in the study, which combined three EMG techniques. A HDsEMG grid covering the entire masseter, and intramuscular fine-wire electrodes were used to obtain two independent MU samples for comparison. The MUs' amplitude profiles in the dimension of muscle depth were determined using scanning EMG. All data were recorded simultaneously during a low, constant contraction level controlled by 3D force feedback.

Results

The median medio-lateral diameter of 4.4 mm (range: 1.2–7.9 mm) for MUs detected by HDsEMG did not differ significantly (Mann-Whitney-U test, p=0.805) from that of 3.9 mm (0.6–8.6 mm) for MUs detected by fine-wire EMG. For individual subjects, the medio-lateral diameters of all HDsEMG-detected MUs spanned 70.5% (19.2–75.1%) of the masseter's thickness.

Conclusions

HDsEMG is able to examine small and large MUs from a great masseter proportion in one single measurement.

Significance

Clinical application of HDsEMG might contribute to a better understanding of neuromuscular adaptations in patients with temporomandibular disorders (TMD) and could allow for monitoring treatment effects.

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