Abstract: There is provided a frame for use with a back support that provides lateral support to an individual while seated to encourage a correct sitting posture, and that also provides lumbar support to the individual that varies according to the individual's size. The frame includes wing portions that act as lateral supports and as torsion bars to cause the center portion of the frame to become convex to support the lumbar region of an individual resting against the back support incorporating the frame. The frame can be incorporated into a portable support unit or to a support unit that is an integral part of a chair.