human body to perform the movement for minimum consumption of energy all joints in the lower extremities are allowed to cooperate and the remaining stump of the prosthesis wearer can cooperate with the at least one movable joint in the leg prosthesis system the leg prosthesis system should supplement the prosthesis wearer and should preferably but not restrictively be controlled by him or her with a leg prosthesis system 1 and or a method according to the invention the disconnectable active drive unit 4 4 u2032 of a knee joint or ankle joint makes it possible for the system and the method to use a combination of active and passive operation the control system 15 can select the optimal method of performing a movement the knee joint 2 can be active while the ankle joint 3 is passive and vice versa for example the knee joint 2 can perform the swinging movement in the swing phase using only the passive brake unit 2 while the ankle joint 3 uses its active drive unit for dorsal flexion of the foot in order to create extra ground clearance fig1 and fig1 are side views in cross section of a knee joint which for instance may be included in the.