A hinge or joint assembly is provided that includes first and second members, a pivot rotatably connecting the first and second members and allowing movement between extension and flexion positions, and at least one elastomeric spring communicating with the first and second members to restrain pivotal movement of the members toward flexion, through compression of the elastomeric spring, and to assist pivotal movement toward extension through decompression of the elastomeric spring. The assembly can further include a disk and lock slide, the disk and lock slide each having complementary teeth providing, when engaged, an arrest of pivotal movement in a direction of flexion and one-way, ratcheting, step-advance pivotal movement in a direction toward extension. The elastomeric spring can be urethane, and can be adapted to mimic any bodily muscle. An embodiment employing a torsional spring is also provided, as is a cable release mechanism providing one-dimensional cable movement.