Pick up just about any magazine on health or fitness and there are guaranteed to be articles on stomach-firming exercises. And it is not really surprising since this is the one stand-out thing that people want - flatter, wash-board stomachs.
Some of the questions these magazines try to answer are why certain people have flatter tummies then others, and how they achieved this. looking at each in turn we can see that the reasons are numerous, but that there are common themes;