(a) Elbow lifting task with the original exoskeleton. An external load is applied at point C, producing a torque T_joint around the human elbow joint (A). The serial 4-bar mechanism, which is connected to the lower arm at point B and anchored at point D, has to produce a torque T_4–bar to compensate for the external load. (b) Addition of a static balancing mechanism in form of springs onto the original design. (c) Mechanical execution of the improved elbow joint. Pictures adapted with permission from Ref. [74].