Sit on bench or seat below two very close high pulleys. Grasp two separate cable stirrups, one with each hand. Pull stirrups down with palms facing back over each shoulder. Holding arms in place, allow weight to pull torso up, hyperextend lower back slightly.
With arms fixed in place, flex waist so shoulders travel forward and downward toward thighs. Return until chest is high and back is hyperextended. Repeat.
Keep arms fixed in position keeping them close to body throughout movement. See Spot Reduction Myth.