Gastrocnemius Muscle Natural Frequencies Estimated from Electrically Induced Mechanomyogram and Anterior-posterior Torque

Abstract

This study aimed to verify whether the natural frequency of the medial gastrocnemius muscle during quiet standing―proportional to the square root of muscle stiffness―estimated from the electrically induced mechanomyogram (MMG), matched that derived from the anterior-posterior torque. Six healthy young male volunteers participated in the experiment. Each participant stood quietly on a force plate while electrical stimulation was applied to the gastrocnemius muscle via disposable surface electrodes. The electrically induced MMG and anterior-posterior torque were recorded and synchronously averaged to eliminate body-sway components from the measured signals. The averaged MMG and torque waveforms were then modeled using a single second-order system and two coupled second-order systems, respectively, and the natural frequency was estimated using a nonlinear least-squares optimization method. The estimated natural frequencies were 2.07 ± 0.15 Hz for the MMG and 2.16 ± 0.14 Hz for the torque. These findings verify that the natural frequency of the medial gastrocnemius muscle derived from the electrically induced MMG closely matches that obtained from the anterior-posterior torque, demonstrating supporting the validity of both approaches for noninvasive assessment of muscle mechanical properties during quiet standing.