Duality Theory: Biduality in Nonconvex Optimization.

A traction frame supports the body of a user in an angularly inclined, inverted position. The traction frame includes a body-supporting frame mounted in a stationary angular position. A leg support beam, extends axially away from the body-supporting frame to an elevated position above the upper end of the frame. A pair of ankle support pads on the beam support the underside of the user's lower legs. A lever arm extends above and parallel to the beam and pivots to the upper end of the beam. A pair of instep support pads on the lever arm can pivot to a locked position in which the user's lower legs are fastened between the instep support pads and the ankle support pads. The lever arm pivots toward the locked position along a guide having a latch engaged by a spring-biased detent in the lever arm. The detent latches in a snap lock to positively prevent the instep pads on the lever arm from rotating away from the ankle support pads. The lever arm can be released from its locked position by pulling axially on the lever arm against the bias of the detent to release the detent from the latch, allowing the lever arm to pivot away.