A wearable apparatus comprises a passive artificial knee that comprises first and second links coupled at a knee joint, a passive compressive force generator coupled to the second link, and a release mechanism coupled to the first link. When an angle of the first and second links is less than a toggle angle, the release mechanism locks in a first operational mode, and the force generator compresses, resisting flexing of the second link. When the angle is larger than the toggle angle, the force generator decompresses and encourages flexion of said second link. When the force generator is extended and said compressive force is small, the release mechanism moves into a second operational mode, wherein the force generator neither resists nor encourages extension and flexion of said second link from said first link. The wearable apparatus comprises an exoskeleton trunk configured to couple to an upper body of a user.
