If you are still performing endless sit ups and crunches in a vein attempt to get a six pack, please stop! Did you know that doing this will not get you a six pack or a flat toned stomach if you have layers of fat there. An unhealthy diet, minimal exercise but 100 sit ups before you go to bed is not going to keep it flat.
Instead, eat healthy foods and keep everything balanced. Exercise a few times a week and slowly you will notice a difference. I still hear and see many people ignoring this sentence and still believing 100 or 200 sit ups is the way. It isn't. Quit the crunches and sort your diet and exercise plan out. Once you start it you will feel better and when you see the results you will never look back :)