Study on the Establishment Process of Muscle Synergy Based on Cosine Similarity

Muscle synergy is an important method for motor intention recognition in rehabilitation exoskeleton control. The use of the non-negative matrix factorization (NMF) to extract muscle synergy patterns often results in long calculation time due to the amount of data, which makes the effectiveness of synergy extraction low. In this paper, synergy matrices of the complete single-cycle signal while stretching and its segmented ones were extracted respectively. By studying the cosine similarity variation of synergy matrices between each continuous segment and the complete single-cycle EMG signals, it is found that there is a "building-stability-weakening" process on muscle synergy establishment. It is proposed to extract synergy mode with partial data from the "stable" segment, rather than using the complete single-cycle one, as similar result to single-cycle data synergy extraction could be obtained. The calculation time of NMF could be optimized by reducing the amount of data and the real-time characteristics of the synergy mode extraction could be improved at the same time. It is of great significance to use synergy matrix of NMF for motion intention recognition and exoskeleton control.Clinical Relevance- This paper studies the establishment process of the synergy mode, and proposes a method for quickly extracting the synergy mode, which can improve the effectiveness of the recognition of motion intention and is of great significance for the real-time control of the rehabilitation exoskeleton.