Muscle-related differences in mechanomyography frequency-force relationships are model dependent

Area of Science:

• Biomechanics
• Physiology
• Motor Control

Background:

• Surface mechanomyography (MMG) is a non-invasive technique to assess muscle activity.
• Mean power frequency (MPF) derived from MMG signals can reflect changes in muscle fiber recruitment and firing rates.
• Understanding the relationship between MMG MPF and force output is crucial for interpreting muscle function.

Purpose of the Study:

• To investigate the mechanomyographic mean power frequency (MMG MPF)-force relationships in the first dorsal interosseous (FDI), vastus lateralis (VL), and rectus femoris (RF) muscles.
• To compare the efficacy of linear regression models applied to absolute and log-transformed MMG MPF values.
• To explore potential influences of skinfold thickness on these relationships.

Main Methods:

• Thirteen healthy males performed isometric ramp contractions (10-80% maximal voluntary contraction).
• MMG sensors were placed on the VL, RF, and FDI muscles.
• Simple linear regression models were applied to absolute and log-transformed MMG MPF-force data; skinfold thickness was measured.

Main Results:

• Log-transformed MMG MPF-force relationships showed significant differences in slopes between the FDI and leg extensors (P < 0.001), unlike the absolute model (P = 0.168).
• Y-intercepts were significantly higher for the FDI compared to leg extensors in both absolute and log-transformed models (P < 0.001).
• No significant correlation was found between Y-intercepts and skinfold thickness, despite observed muscle-related differences.

Conclusions:

• Log-transformed analysis is superior for quantifying differences in MMG MPF-force relationships between distinct muscle groups like the FDI and leg extensors.
• The log-transformed model reveals unique response patterns not discernible with absolute values.
• While skinfold thickness influences MMG signal characteristics (Y-intercepts), it does not directly correlate with the observed force-dependent changes in MPF patterns.