The so-called Roman chair is little more than a padded hip rest mounted at an angle. On the spectrum of back stabilization exercises, the Roman chair is fairly difficult -- so it isn't always appropriate for those with back problems. If you've been cleared to do this exercise, you'll be best off with a Roman chair that lets you adjust its angle, thus changing the intensity of the exercise.
Proper Form
Adjust the hip pad so it's about 3 inches below your belt buckle, then lean against it and hinge forward from the hips, keeping your back straight. Squeeze your glutes to bring yourself back to the starting position, completing one repetition. Adjustable-incline Roman chairs are best because they're an easy way to adjust your workout intensity; as you adjust the chair toward a more vertical tilt, the exercise becomes easier.
Identify Your Back Problem
Your glutes, or butt muscles, actually do most of the work during a Roman chair exercise. Your back muscles are mostly along for the ride to stabilize your upper body. Although some medical professionals do recommend Roman chair exercises for resolving back pain, it depends on what's causing the pain. So before you start your workout, check with your doctor to get your back problem properly diagnosed.