Systems, methods, and apparatus provide artificial knees. Artificial knees include a thigh link configured to move in unison with a thigh of the person, a shank link configured to be rotatably coupled to said thigh link, and a compression spring rotatably coupled to the thigh link and coupled to a second end of shank link with a second end of the compression spring. During a first range of motion, the compression spring is configured to provide an extension torque between the thigh link and the shank link causing said artificial knee to resist flexion. After said first range of motion, the compression spring is configured to provide a flexion torque between the thigh link and the shank link encouraging said artificial knee to flex resulting in toe clearance during the swing phase. During the swing phase, the compression spring provides no torque between the thigh link and the shank link.
