A wavelet-based analysis of surface mechanomyographic signals from the quadriceps femoris

The purpose of this study was to use a wavelet analysis designed specifically for surface mechanomyographic (MMG) signals to examine the MMG responses of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Fifteen healthy men [age (mean +/- SD): 26.4 +/- 6.1 years] volunteered to perform isometric muscle actions of the dominant leg extensors at 20%, 40%, 60%, 80%, and 100% of the maximum voluntary contraction (MVC). During each muscle action, surface MMG signals were detected from the VL, RF, and VM and processed with the MMG wavelet analysis. The results show that, for the VL and VM muscles, there was compression of the total MMG intensity spectra toward low frequencies for most force levels above 20% MVC. For the RF, however, the peak of the total MMG intensity spectrum occurred at approximately 30-40 HZ for all force levels. Because the VL, RF, and VM are all innervated by the femoral nerve, the discrepancies among the three muscles for total MMG intensity in each wavelet band may have been due to differences in architecture, muscle stiffness, and/or intramuscular pressure.