An exoskeleton includes first and second support structures configured to be coupled to a wearer of the exoskeleton. A joint connects the first and second support structures, the joint enabling relative movement between the first and second structures. First and second cord loops connect the first and second support structures. At least one motor twists and thereby shortens the first and second cord loops, wherein shortening of the first cord loop causes relative movement of the first and second support structures about the joint in a first direction, and shortening of the second cord loop causes relative movement of the first and second support structures about the joint in a second, opposite direction. A brake mechanism prevents relative movement of the first and second support structures about the joint in at least one of the first and second directions if one of the first and second cord loops breaks.