Seo Toolbar by Sit Up Bench - Version 1.0 Sit up bench workouts develop abdominal muscles from a slightly different angle than floor exercises, utilizing leverage and gravity to help build the burn. Straight Leg Raise Sit Up Bench ExerciseDoing a straight leg raises on a sit up bench could put strain on your lower-back, so be sure to move slowly through the exercise if you are prone to back pain. Start by laying on your back-side, grabbing the sides of the bench just under your head. Keep your legs together and raise them straight up, bending at the waist and making sure to keep your legs straight. Now lower your legs back down, and be sure not to rest them on the bench. Advance exercise enthusiasts may want to move their body down the bench, hanging their legs off the end. This vastly increases the difficulty of the exercise.