Superimposed Mechanomyographic Response at Different Contraction Intensity in Medial Gastrocnemius and Soleus Muscles

Abstract

This study examined changes in mechanical properties of medial gastrocnemius muscle (MG) and soleus muscle (SOL) at different contraction intensities using superimposed mechanomyogram (MMG) signals. The subjects were measured for the superimposed twitch amplitude and peak acceleration of the twitch torque development (d²T /dt²) from electrical stimulation of the posterior tibial nerve during isometric plantar flexions at 20%, 40%, 60%, 80%, and 100% of maximal voluntary contraction (MVC). In addition, the superimposed MMG amplitude was recorded from MG and SOL. The superimposed twitch amplitude, d²T /dt² and superimposed MMG amplitude of MG and SOL decreased with increasing %MVC. With increasing %MVC, changes in the pattern of superimposed MMG of the MG were similar to the changes in the pattern of d²T /dt². There were significant relationships between the superimposed twitch amplitude and the superimposed MMG amplitude of MG and SOL, and the d²T /dt² and superimposed MMG amplitude of MG and SOL. The normalized superimposed MMG amplitude of the MG at 20% and 40% of MVC is significantly higher than that of SOL. These results suggest that superimposed MMG signals recorded from synergistic muscle (MG and SOL) reflects individual mechanical activation levels at lower contraction intensity.