Fig. 3.
Stiffness ellipses (top figures) and corresponding joint stiffness values (bottom figures) of subject A during posture maintenance tasks (a–f) in five different postures (DC, distal center; MC, middle center;PC, proximal center; PL, proximal left;PR, proximal right). Each ellipse represents the stiffness during the requested task indexed by a roman character: (a) without cocontraction, (b) with quarter cocontraction, (c) half cocontraction, (d) full cocontraction, (e) cocontraction only in the shoulder, and (f) cocontraction only in the elbow. The thick line represents the arm configuration in each posture. The bottom graphsrepresent the stiffness values (Rss,solid black line; Rse,dashed green line; Res,dotted blue line; Ree,dash-dot red line) during each task (a–f) at the hand positions [theleft graph is for DC (circle), MC (star), and PC (square); the right graph is for PL (diamond) and PR (triangle)]. The error bars represent the SD of estimates.