A lower extremity exoskeleton, configurable to be coupled to a person, comprises two leg supports configurable to be coupled to the person's lower limbs and configured to rest on the ground during their stance phases. Each leg support comprises a thigh link, a shank link, and two knee joints. Each knee joint is configured to allow flexion and extension between the respective shank link and the respective thigh link. The lower extremity exoskeleton also comprises an exoskeleton trunk configurable to be coupled to the person's upper body. The exoskeleton trunk is rotatably connectable to the thigh links of the leg supports allowing for the flexion and extension between the leg supports and the exoskeleton trunk. In this exemplary embodiment, the energy required for flexion and extension movement between the shank link and the respective thigh link of a leg support over a cyclic knee motion is provided by the person.