A lower limb prosthesis (10; 110; 210; 310) comprising: a distal end comprising a prosthetic foot; a proximal end at a distance from the distal end, the lower limb prosthesis (10; 110; 210; 310) defining a length between the distal end and the proximal end (14, 12); and a first actuator (18; 118; 218) between the proximal end and the distal end, the first actuator (18; 118; 218) comprising a linear extension and retraction mechanism configured to extend and retract a segment (16; 116; 216; 316) of the lower limb prosthesis (10; 110; 210; 310) between the proximal end and the distal end and thereby modify the length of the lower limb prosthesis (10; 110; 210; 310) between the distal end and the proximal end; characterized by a control system in communication with the first actuator (18; 118; 218), the communication being configured to cyclically modify the length of the lower limb prosthesis (10; 110; 210; 310) through a single gait cycle, the single gait cycle comprising a stance phase and a swing phase, wherein the cyclic modification includes extension of the segment (16; 116; 216; 316) to increase the length of the lower limb prosthesis (10; 110; 210; 310) in preparation for heel strike on a surface, retraction of the segment (16; 116; 216; 316) to decrease the length of the lower limb prosthesis (10; 110; 210; 310) during the stance phase during which the prosthetic foot is in contact with the surface, extension of the segment (16; 116; 216; 316) to increase the length of the lower limb prosthesis (10; 110; 210; 310) at an end of the stance phase that includes immediately prior to and during a loss of contact between the prosthetic foot and the surface, and retraction of the segment (16; 116; 216; 316) to decrease the length of the lower limb prosthesis (10; 110; 210; 310) during the swing phase, wherein all extension and retraction of the segment (16; 116; 216; 316) is under the control of the actuator (18; 118; 218) and the control system. a distal end comprising a prosthetic foot; a proximal end at a distance from the distal end, the lower limb prosthesis (10; 110; 210; 310) defining a length between the distal end and the proximal end (14, 12); and a first actuator (18; 118; 218) between the proximal end and the distal end, the first actuator (18; 118; 218) comprising a linear extension and retraction mechanism configured to extend and retract a segment (16; 116; 216; 316) of the lower limb prosthesis (10; 110; 210; 310) between the proximal end and the distal end and thereby modify the length of the lower limb prosthesis (10; 110; 210; 310) between the distal end and the proximal end; characterized by a control system in communication with the first actuator (18; 118; 218), the communication being configured to cyclically modify the length of the lower limb prosthesis (10; 110; 210; 310) through a single gait cycle, the single gait cycle comprising a stance phase and a swing phase, wherein the cyclic modification includes extension of the segment (16; 116; 216; 316) to increase the length of the lower limb prosthesis (10; 110; 210; 310) in preparation for heel strike on a surface, retraction of the segment (16; 116; 216; 316) to decrease the length of the lower limb prosthesis (10; 110; 210; 310) during the stance phase during which the prosthetic foot is in contact with the surface, extension of the segment (16; 116; 216; 316) to increase the length of the lower limb prosthesis (10; 110; 210; 310) at an end of the stance phase that includes immediately prior to and during a loss of contact between the prosthetic foot and the surface, and retraction of the segment (16; 116; 216; 316) to decrease the length of the lower limb prosthesis (10; 110; 210; 310) during the swing phase, wherein all extension and retraction of the segment (16; 116; 216; 316) is under the control of the actuator (18; 118; 218) and the control system.