It is really useful. The first time I did it, I couldn't even do a set of movements on the first day, because my abdominal muscles really hurt and I couldn't persist. Later, it took two days to get used to it, so the first set of movements last night could be done continuously. Then it lasted for 7 days and the upper and lower abdominal muscles were effective. I persisted for many, many days, and the effect was really good. Practical, awesome!