Fig. 7.

Joint phase plot between elbow flexion/extension angle and shoulder flexion/extension angle while the subject was performing (A) arm reaching up task and (B) then arm retracting. Zero in the vertical axis for elbow flexion and extension denotes full elbow extension. Horizontal and vertical lines indicate a single DOF moving, while slope areas are the phases of coactivation or joint synergy (ie, 2 joints moving together). The red stars indicate the initial joint position.