On the Robustness of Muscle Synergies in the Lower Extremity for Human-Exoskeletons Interaction

Abstract

Accurately recognizing the user's expected action and converting it into a control signal is critical to the effectiveness of exoskeleton control. Inspired by the natural human movement, an alternative method based on muscle synergies has received increasing attention in myoelectric control in robotic exoskeletons. For the muscle synergies based control system, robust and reliable synergies structures are crucial. Therefore, this paper investigated whether robust muscle synergies could be extracted in the lower limb with three daily activities. Firstly, ten channels of lower extremity surface electromyographic (sEMG) signals were recorded from five healthy subjects during movements. Then, the non-negative matrix factorization (NMF) approach was used to extract the muscle synergies, and the variance accounted for (VAF) method was used to count the number of synergies. Finally, cosine similarity (CS) and synergy stability index (SSI) were used to evaluate the robustness. The resulting high SSI and CS scores demonstrated the robustness and reliability of muscle synergy in typical lower extremity tasks. These findings provide valuable insights for developing muscle synergies based assistive technology for human exoskeletons interaction.