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

The purpose of this study was to examine the surface mechanomyographic mean power frequency (MMG MPF)-force relationships with linear regression models applied to the absolute and log-transformed values for the first dorsal interosseous (FDI), vastus lateralis (VL) and rectus femoris (RF) muscles. Thirteen healthy males performed isometric ramp contractions of the leg extensors and index finger from 10 to 80% of their maximal voluntary contraction with MMG sensors positioned on the VL, RF, and FDI. Simple linear regression models were fit to the absolute and log-transformed MMG MPF-force relationships. Skinfold thickness measurements were taken at each sensor site. There were significant differences for the slopes from the log-transformed MMG MPF-force relationships between the FDI and the leg extensors (P < 0.001) but not the absolute model (P = 0.168). The Y-intercepts were greater for the FDI than the leg extensors for the absolute (P < 0.001) and log-transformed models (P < 0.001), which reflected similar muscle-related differences (P < 0.001) for skinfold thickness. However, there were no significant correlations between Y-intercepts and skinfold thicknesses. Differences in the patterns of response between the FDI and leg extensors were only quantified with the log-transformed model.