An actuator subsystem preferably for a robot or bionic linkage. A joint between two robotic or bionic members includes at least first and second actuators such as piston-cylinder assemblies connected between the members. A hydraulic circuit includes a sensor subsystem for sensing the magnitude of the load on the piston-cylinder assemblies and/or members. A fluid supply system includes an actuatable control valve operable to supply fluid to one or both piston-cylinder assemblies. A control circuit is responsive to the sensor and is configured to electronically control the fluid subsystem to supply fluid to the first piston-cylinder assembly when the sensor subsystem senses a load below a predetermined magnitude and to supply fluid to both piston-cylinder assemblies when the sensor subsystem senses a load above the predetermined magnitude.