I know it sounds crazy, but it really does exercise your inner core muscles... all you have to do is keep breathing! As you breathe in and out, and your chest & tummy go up and down you are exercising! I learned about this while taking a pain management class at our local hospital. The class was developed by an RN, who has gone on to bigger things now since her methods are simple, doable, and actually help people!
You have to do it more than once, tho!