Reliability of mechanomyographic amplitude and mean power frequency during isometric step and ramp muscle actions

This study examined the reliability of mechanomyographic amplitude (MMGRMS) and mean power frequency (MMGMPF) for the vastus lateralis during isometric maximal voluntary contractions (MVCs) and submaximal step and ramp muscle actions of the leg extensors. Nineteen participants (mean ± S.D. age = 24 ± 4 yrs) performed two isometric MVCs, 10 randomly ordered isometric step muscle actions at 5, 15, 25, 35, 45, 55, 65, 75, 85, and 95% of MVC, and two 6 s isometric ramp muscle actions during 3 trials separated by 3–5 days. The intraclass correlation coefficient (ICC), standard error of the measurement (SEM), and minimal difference (MD) were used for test–retest reliability, while repeated measures ANOVAs were used to quantify systematic variability. Systematic variability was only present across the 3 trials at 5% MVC during the step muscle action for MMGRMS and at 35% of MVC during the ramp muscle action for MMGMPF. The ICCs ranged from 0.39 to 0.89 and 0.36 to 0.80, while the SEM (% of mean) ranged from 14.9 to 33.9% and 6.9 to18.9% for MMGRMS and MMGMPF, respectively. Thus, MMGRMS and MMGMPF demonstrated reliability that was comparable to that of the surface electromyographic signal.