Here is another Pilates abdominal exercise that is a regular in my workout rotation. If you don't have a Pilates ball, you can also do this on a bosu. The most important part of the exercise is the breathing and contraction. There should be a strong exhale and contraction at the top of the movement. The placement of the ball or bosu is also very important. If it hurts your lower back, either the ball is is the wrong place, or you're not contracting properly. Check with a personal trainer or Pila