An exercise machine applicable for strengthening a user's abdominal muscles is described. The exercise machine can include a base frame, a seat assembly and a backrest assembly rotatably coupled with the base frame. The base frame can include side members and a crossbar member to provide floor support. The backrest assembly may be configured to swivel with rotational movements around at least one axis of rotation. The backrest assembly may include at least one swivel structure and two handle bars. Each swivel structure may be rotatable around a separate axis of rotation. The handle bars may be mounted substantially transverse to a particular axis of rotation. The seat assembly can include a seat pad affixed to the crossbar member to allow a user sitting on the seat pad to cause the swiveling of the backrest assembly via hand pushes on the handle bars.