Effect of region‐specific functional roles within lower limb muscles on muscle synergies extraction =

Muscle synergies are a widely recognized model of how the central nervous system overcomes the redundancy of the musculoskeletal system. Usually they are studied from surface EMG sampling one EMG signal from each muscle involved in the considered movement. However, specific studies showed that separated regions of some lower limb muscles (rectus femoris and vastus medialis for instance) may be excited independently. If, during a given motor task, different regions of the same muscle are elicited at different instants, it is then possible that a single muscle participates in different synergies. In this study, the main focus is extracting muscle synergies considering different regions of selected lower-limb muscles as totally distinct actuators. Multichannel sEMG detection has been used to simulate the sampling of these muscles’ activity from different locations and with different pick-up volumes and to check if different portions of the same muscle are involved in different synergies. Eight healthy subjects participated in the study. EMG signals were detected from 8 muscles (Rectus Femoris, Vast Medialis, Gluteus Medius, Biceps Femoris, Tibialis Anterior, Gastrocnemius Medialis and Soleus) during over ground gait at self-selected speed, gait on treadmill at pre-selected speed and cycling on a stationary bike at a pre-chosen pace and fixed resistance. Multiple electrodes were positioned on Rectus Femoris, Vastus Medialis and Soleus with the specific focus of detecting differences in the regional EMG activation, distinguishing proximal and lateral portions for the first two, medialis and lateralis for Soleus. Muscle synergies extraction was performed with Matlab 2017a NNMF (Non Negative Matrix Factorization) routine.