The best starting position and technique for you will depend on your current level of conditioning and your goal. The Roman chair apparatus is also called the “glute-ham developer” because of its role in working the posterior chain muscle groups when the body is in a certain position.
First, determine if you want to work only your back or if you want to include the back, gluteals, and hamstrings in the exercise. To focus the work on the back, position the hips on top of the pad so that they remain stable as the trunk lowers and raises. In this position, the hips are blocked from being able to flex, which means that the glutes and hamstrings will play only a minor role in the movement. To work the back, start at a position where the back is neutral and parallel with the ground. Slowly lower the trunk toward the floor and raise it back up to parallel. The back should remain neutral throughout the lower and the lift phases. Only lower the trunk as far as you can keep the spine in a neutral position, which will depend largely on flexibility. If you feel the spine starting to round forward, you’ve gone too far for what your stability and flexibility will allow. After several weeks of practice, you may rise above parallel (hyperextension), but realize that this position puts additional stress on the lumbar spine and is not recommended for those who have back problems.
If you determine that you would like to get the glutes and hamstrings more involved, position the hips beyond the pad so that they are able to flex and extend without interference. In this position, you will immediately feel the difference as more tension is created in the glutes and hamstrings as the work along with the back to hold up the trunk parallel to the floor. Follow the same technique as described above, paying careful attention to keeping your back in a neutral, stable position. Also, for both exercise positions, be sure to keep the movement speed slow and controlled.
Lastly, be aware that these exercises place a tremendous amount of eccentric load on the posterior muscles, which is the type of load that causes the most delayed onset muscular soreness. In other words, don’t be surprised if you are exceptionally sore for a day or two after performing exercises on the Roman chair.