Muscle synergy analysis for similar upper limb motion tasks.

Muscle synergy is considered as a vector specifying a pattern of relative muscle activation. The goal of this paper is to explore whether there exists similarities between muscle synergies in similar upper limb motion tasks. One center-out-center reaching task and two path movement tasks with regard to the elbow and shoulder joints were designed, and seven healthy adults were recruited in this study. Surface electromyographic (sEMG) signals were recorded from 10 upper arm and shoulder muscles, and muscle synergies were extracted using nonnegative matrix factorization algorithm. Although there existed individual differences among subjects, experimental results showed that the structures of muscle synergies extracted from these three similar tasks were similar on the ground of the values of Pearson's correlation coefficient was greater than 0.85. Through this finding, the neuromuscular control strategies of upper limb in similar tasks could be explained clearly, which also provided significant evidence to support the hypothesis of muscle synergies.