An arm supporting exoskeleton comprises a shoulder base coupled to an arm link mechanism. The arm link mechanism comprises a proximal link and a distal link configured to rotate relative to each other about a rotating joint； at least one arm-coupler adapted to couple a user's arm to the distal link； a tensile force generator coupled to the proximal link and the distal link, and providing a torque to flex the distal link relative to the proximal link； and a protrusion located substantially at the rotating joint. When the distal link extends past a toggle angle, the protrusion constrains the tensile force generator, and the torque provided by the tensile force generator remains substantially small. When the protrusion does not constrain the tensile force generator, the torque tends to flex the distal link relative to the proximal link, thereby reducing human shoulder forces and torques required to raise the arm.
