Spatial and force dependency of mechanomyographic signal features

Area of Science:

• Biomechanics
• Motor Control
• Biomedical Engineering

Background:

• Surface mechanomyography (MMG) is used to assess muscle activity.
• Previous studies often use single-point MMG, potentially overlooking spatial variations.
• Understanding spatial inhomogeneity is crucial for accurate muscle function assessment.

Purpose of the Study:

• To investigate the spatial inhomogeneity of surface MMG signals during isometric contractions at varying force levels.
• To analyze how temporal and spectral MMG descriptors change across the muscle surface.
• To evaluate the impact of spatial variations on MMG-based motor unit control assessments.

Main Methods:

• Utilized a novel 5x3 accelerometer grid to record MMG from the tibialis anterior muscle in 10 volunteers.
• Subjects performed isometric contractions at incremental force levels (0-100% maximal voluntary contraction).
• Computed spatial maps of MMG descriptors (amplitude, spectral features) and analyzed centroid and entropy to quantify spatial distribution and homogeneity.

Main Results:

• Normalized MMG amplitude and spectral features showed spatial dependency, with centroids shifting as force increased.
• MMG amplitude increased with force, while its spatial homogeneity (entropy) decreased.
• The relationship between force and MMG characteristics was significantly influenced by the recording location on the muscle.

Conclusions:

• Surface MMG signals exhibit significant spatial inhomogeneity during muscle contractions.
• Single-channel MMG measurements may not fully capture muscle activation dynamics due to location-dependent signal variations.
• These findings underscore the importance of considering spatial MMG mapping for a comprehensive understanding of muscle force production and motor control.