Investigating the spatial resolution of EMG and MMG based on a systemic multi-scale model

TL;DR

This study develops a systemic multi-scale model to compare EMG and MMG signals, revealing that MMG, especially the normal-to-surface component, offers superior spatial selectivity in non-invasive measurements, with minimal influence from subcutaneous fat.

Contribution

The paper introduces the first comprehensive in silico model comparing EMG and MMG, highlighting MMG's advantages in spatial selectivity and analyzing structural contributions to the magnetic field.

Findings

MMG outperforms EMG in non-invasive spatial selectivity.

Normal-to-surface MMG component is minimally affected by subcutaneous fat.

Passive muscle fibers significantly contribute to the magnetic field.

Abstract

While electromyography (EMG) and magnetomyography (MMG) are both methods to measure the electrical activity of skeletal muscles, no systematic comparison between both signals exists. Within this work, we propose a systemic in silico model for EMG and MMG and test the hypothesis that MMG surpasses EMG in terms of spatial selectivity. The results show that MMG provides a slightly better spatial selectivity than EMG when recorded directly on the muscle surface. However, there is a remarkable difference in spatial selectivity for non-invasive surface measurements. The spatial selectivity of the MMG components aligned with the muscle fibres and normal to the body surface outperforms the spatial selectivity of surface EMG. Particularly, for the MMG's normal-to-the-surface component the influence of subcutaneous fat is minimal. Further, for the first time, we analyse the contribution of different structural components, i.e., muscle fibres from different motor units and the extracellular space, to the measurable biomagnetic field. Notably, the simulations show that the normal-to-the-surface MMG component, the contribution from volume currents in the extracellular space and in surrounding inactive tissues is negligible. Further, our model predicts a surprisingly high contribution of the passive muscle fibres to the observable magnetic field.