Mechanomyographic amplitude and mean power frequency responses during isometric ramp vs. step muscle actions

Abstract

The purpose of the present study was to compare the mechanomyographic amplitude (MMG RMS) and mean power frequency (MMG MPF) vs. torque relationships during isometric ramp and step muscle actions for the vastus lateralis (VL) and rectus femoris (RF) muscles. Nineteen subjects (mean ± S.D. age = 24 ± 4 years) performed 2 isometric maximal voluntary contractions (MVCs) before and after 2 or 3 isometric ramp muscle actions from (5–95% MVC) to 9 submaximal step muscle actions (15, 25, 35, 45, 55, 65, 75, 85, and 95% MVC). MMG signals were recorded from the VL and RF muscles, and MMG RMS and MMG MPF values were computed for each corresponding percentage of the MVC. Absolute and normalized MMG RMS and MMG MPF vs. torque relationships were analyzed and interpreted on a subject-by-subject and composite pattern basis using polynomial regression and repeated measures ANOVAs. For MMG RMS and MMG MPF, only 16–53% and 11–26% of the individual responses were consistent with the composite polynomial models, respectively. In addition, the normalized composite MMG RMS values were greater for the RF than the VL from 35 to 85% MVC. Only 47% of the MMG RMS and 5% of the MMG MPF individual patterns of responses were the same for the ramp and step muscle actions, and differences were also observed for the composite MMG RMS and MMG MPF patterns between the ramp and step muscle actions. Overall, these findings indicated that the torque-related patterns of responses for MMG RMS and MMG MPF were different among subjects (i.e., inter-individual variability) and were muscle- (VL vs. RF) and mode-specific (ramp vs. step).