In the present study, the activity of isolated motor units (MUs) in the rat soleus (SOL) muscle was evoked by stimulation of thin filaments of ventral roots using constant and irregular frequency stimulation patterns. The MUs force, action potentials, and mechanomyograms (MMG) were recorded. MMG profiles were recorded with a laser distance sensor (LDS), categorized and compared with profiles obtained in a similar experiment performed on the medial gastrocnemius (MG) muscle. The profiles and amplitudes of the MMG signal vary greatly depending on the type of stimulated MU, contraction, and LDS localization. Compared to previously obtained results for MG, where three general types of MMG signal were distinguished, in the case of SOL the signal polyphasic signal profile was observed for weak contraction. The steady‑state MMG‑contraction force relationship could be successfully approximated with a third‑order polynomial model. Nevertheless, the model parameters were not constant and changed with stimulation type. The observed phenomena were also analyzed with a 3D model utilizing the Finite Element Method. In vivo and simulation results suggested that MMG was an effect of superposition of several movements types evoked by contraction (muscle belly rotation, transverse shearing due to non-axial localization of MUs, local surface deformation). The proposed model set to explain the most likely origins of differences in the MMG profile between MG and SOL muscles. These observations were used to create a novel method of transcutaneous MMG measurement, based on 9‑degree of freedom inertial sensors. The technique was applied to the classification of 6 hand gestures based on the MMG signal.