Fig. 4

Number and composition of muscle synergies. A The gVAF values (mean ± SD) of the stroke (orange) and the control (green) groups. An asterisk represents a statistical difference between the two groups (Wilcoxon rank-sum test, p < 0.050). The mean composition of B five synergies (C1 ~ C5) of the control group, C four synergies (S1 ~ S4) of the stroke group, and D five synergies (S1' ~ S5') of the stroke group. Standard deviations are represented as error bars. The numbers to the right of the graphs represent the mean similarity of the individual synergy vector and the similarity of the set of synergy vectors of stroke participants to the mean synergy vectors of the control group. An asterisk represents a statistical difference between each similarity value and its corresponding similarity by chance (Sign test, p < 0.050). E Mean merging coefficients of five to four stroke synergy vectors. The merging coefficients above 0.2 are considered as a significant merging of synergies. UT upper trapezius, LT lower trapezius, SS supraspinatus, IS infraspinatus, PM pectoralis major, MD middle head of deltoid, AD anterior head of deltoid, PD posterior head of deltoid, Tlo long head of triceps, Tla lateral head of triceps, Bic biceps, Brd brachioradialis, Brc brachialis