Abstract: A leg for use on hopping, running, jumping and walking machines. As incorporated into the bow leg hopper robot, a thrust actuator provides elastic energy to the leg which is automatically released during stance to control hopping height. Lateral motion is controlled by directing the leg angle at touchdown, which determines the angle of takeoff. The leg pivots freely on a hip bearing, and is automatically decoupled from the leg-angle positioner during stance to preclude hip torques that would disturb body attitude. Upright attitude is maintained without active control by allowing the body to hang from the hip joint. The leg may also be incorporated into multilegged running robots, and recreational vehicles.