A system comprises one or more wearable devices including a first body interface adapted to be secured to a first bodily part. A second body interface is adapted to be secured to a second bodily part separated from the first bodily part by a physiological joint. One or more joints provide one or more degrees of freedom between the first body interface and the second body interface. A magnetorheological (MR) fluid actuator unit comprises one or more power sources. An MR fluid clutch apparatus receiving torque from the at least one power source, the at least one MR fluid clutch apparatus operable to generate a variable amount of torque transmission when subjected to a magnetic field. A transmission couples the MR fluid actuator unit to the wearable device for converting torque from the MR fluid actuator unit to relative movement of the body interfaces with respect to one another.