Fig. 1
Experimental setup. A Subject seated at the horizontal planar robotic testing system. The system included the robotic tool as well as a horizontal planar feedback display and electromyography sensors (not shown). B Representative left-hand workspace with sampling points. The robot enforced transitions between targets along paths designed such that motion of the subject’s arm occurred predominantly at one joint (either the shoulder or elbow) while the other joint remained essentially still. Dashed and solid purple arcs: exemplar elbow and shoulder trajectories, respectively. Detailed analyses were performed at selected sample locations labeled as boundary (B1 through B6, blue circles) or center points (C1 through C3, red circles). Interior points are shown in black. Red dotted line: a transition analyzed in greater detail below (Fig. 3). C Representative right-hand workspace with sampling points. Note that the left- and right-arm workspaces and joint angle definitions (θS and θE) were mirror-symmetric such that the hand was at boundary point B4 when the shoulder and elbow both were flexed to the maximum extent allowed by the subject’s passive range of motion and/or the robot’s workspace