Mechanomyographic amplitude and frequency vs. isometric torque relationships in women with higher vs. lower strength

OBJECTIVE: The study examined mechanomyographic (MMG) amplitude(root mean square, RMS) and mean power frequency (MPF) vs. torque relationships during isometric muscle actions in women with higher vs. lower strength. METHODS: Eighteen women volunteered to perform isometric leg extensions at 10 to 100% of their maximal voluntary contraction (MVC) on an isokinetic dynamometer. The women were classified into lower strength (n = 10) and higher strength (n= 8) groups based on their isometric MVC values(lower = 98.4 ± 18.3 Nm, higher = 162.8 ± 26.1 Nm). An accelerometer was placed over the vastus lateralis to detect the MMG amplitude (RMS) and frequency (MPF). Torque (Nm) was recorded by the dynamometer. RESULTS: Polynomial regression analyses indicated the relationship for normalized MMG amplitude vs. isometric MVC was quadratic for the lower strength group (R 2 = 0.989) and linear for the higher strength group(R 2 = 0.917). The MMG amplitude of lower strength women increased most between 60 and 100% MVC. For MMG MPF, the relationships were linear for both lower (R 2 = 0.495) and higher strength women (R 2 = 0.824). CONCLUSIONS: The different torque-related responses of MMG amplitude for lower vs. higher strength women likely reflected differences in absolute torque, and thus muscle stiffness, between groups.