Articulation devices, systems, and methods for articulating elongate flexible structures can locally contract a flexible elongate frame or skeleton of an elongate flexible body such as a catheter. Balloons along one side of an axial segment of the elongate flexible body can be inflated so as to help define a resting shape of the elongate body. The skeleton may have pairs of corresponding axially oriented surface regions coupled to each other by a loop of a deformable helical coil structure. Balloons may be between the regions, and the pairs may be separated by an offset that increases when the axis of the skeleton is axially compressed. Inflation of the balloons can axially contract or shorten the skeleton adjacent the balloons so that the elongate body bends toward the balloons. Different sets of balloons may apply opposing local axial elongation and contraction forces so that selective inflation and deflation of subsets of the balloons can controllably bend and/or change an overall axial length of the elongate body throughout a workspace. Varying the inflation pressures of the opposed balloons can controllably and locally modulate the stiffness of the elongate body.
