According to Diet Spotlight, the ab swing allows a person to work their obliques and abs in an upright position by moving their lower and upper halves as they pivot on the seat. It has a swing and a seat that is on a pivot with a frame.
The frame has a handle on each side and a bar that extends from the seat to the floor. To use the ab swing, a person begins by sitting on the seat, grasping the handles and then placing his feet in the stirrups that are on the bar near the floor. Then he keeps his knees bent, crunches forward and pulls the knees to his chest. Then he lowers his legs and repeats. This method of using the ab swing works the entire abdominal wall.
Another method of using it is to keep the upper body upright and contract the lower abdominal muscles as the knees are pulled to the chest by tilting the seat backwards. This position is meant to be held briefly, then released and repeated. This method works the lower portion of a persons abdominal muscles. The ab swing exercises are to be performed in slow, controlled movements to reduce the chance of injury.