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

The purpose of the present study was to compare the mechanomyographic amplitude (MMGRMS) and mean power frequency (MMGMPF) 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 MMGRMS and MMGMPF values were computed for each corresponding percentage of the MVC. Absolute and normalized MMGRMS and MMGMPF vs. torque relationships were analyzed and interpreted on a subject-by-subject and composite pattern basis using polynomial regression and repeated measures ANOVAs. For MMGRMS and MMGMPF, only 16–53% and 11–26% of the individual responses were consistent with the composite polynomial models, respectively. In addition, the normalized composite MMGRMS values were greater for the RF than the VL from 35 to 85% MVC. Only 47% of the MMGRMS and 5% of the MMGMPF individual patterns of responses were the same for the ramp and step muscle actions, and differences were also observed for the composite MMGRMS and MMGMPF patterns between the ramp and step muscle actions. Overall, these findings indicated that the torque-related patterns of responses for MMGRMS and MMGMPF were different among subjects (i.e., inter-individual variability) and were muscle- (VL vs. RF) and mode-specific (ramp vs. step).