An actuator device, a method and a system for limb rehabilitation, and a pneumatic actuator element. The actuator device for limb rehabilitation comprises one or more pneumatic actuator elements； and means for coupling the pneumatic actuator elements to the limb at or near one or more joints of the limb； wherein each pneumatic actuator element comprises: an expandable main body having a longitudinal axis； one or more channel networks formed in the main body such that, in an acquiescent state of the pneumatic actuator element, a projected length of each channel network along the longitudinal axis is shorter than a total channel length of said each channel network.
