Highly effective instrument for strengthening the abdominals. You have to go gradually increasing the As the number of sets as hard to hold 5 minutes once. Pleasant surprise, during a visit to my physio, I saw he had the device and according to him, it's really the best way to work the abdominal muscles effectively. We must be careful against by to position his back (the round and not dig) to avoid getting hurt. The whole family adopted it, each according to his abilities.