This exercise primarily works the lower back.
1. Begin by getting onto the machine, locking your heels below the stops and lowering your upper body as far down as you can, relaxing at the hips.
2. Raise your body to at least horizontal or higher if you can; do not raise so high as to put painful pressure on your spine. Do not jerk during the exercise; keep a slow, fluid, steady motion.
Ending position: note that this shows a weight plate behind the head in case you wish to increase intensity. You can either hold the plate like this or touching the chest in front.