Figure 1.

Experimental setup. (A) Display; (B) screen table; (C) EMG signals; (D) muscle synergies [u_R(s) (top left), u_φ(s) (top right), and u_φ×R(s) (bottom left)]; (E) endpoint-stiffness ellipse; (F) equilibrium point. The subject performed spiral or circle tracing with the non-dominant/dominant hand in a horizontal plane while monitoring a display showing the ideal trajectory. The EMG activities during movements were recorded to analyze muscle synergies, endpoint stiffness, and virtual trajectories.