Various embodiments of the invention relate to orthotic apparatuses configured to apply a controllable, therapeutic force to a subject. In one embodiment of the invention, an orthotic apparatus includes a frame structure and an actuator system operable to provide input energy of a first type (e.g., fluid pumped by a pump or an applied voltage). At least one strap structure is attached to the frame structure and operably coupled to the actuator system. The at least one strap structure may be configured to convert at least a portion of the input energy to energy of a second type, the energy of the second type being strain energy. Additional embodiments are directed to inflatable structures and methods of operating the orthotic apparatuses and inflatable structures disclosed herein.