Lie on your side on a Roman Chair or use a bench. Your hips and legs are supported by the Roman Chair or bench, and your trunk is off the bench. In the case of a normal bench, you will need someone to hold your feet. In the case of the Roman Chair, hook your feet under the heel pad. Cross arms over chest. If using weight, hold weight plate at chest level. Lower the body down, maintaining this sideways position. Go as far down as is safe and comfortable and return to the starting position.
Here are a few suggested alternative exercises:Ab Crunch ObliquesBall Crunch TraditionalDumbbell Side BendsLateral Bend with Barbell