A combined active and passive leg prosthesis system, and a method ofperforming a gait cycle by a leg prosthesis system (1), for replacing amissing lower extremity of an individual to perform a gait cycle by the legprosthesis system and/or the method (1). The leg prosthesis system (1) has atleast one movable joint (2, 3), a disconnectable active drive unit (4, 4') todrive the movable joint and a passive brake unit to brake the movable joint(2, 3) when the drive unit (4, 4') is disconnected.