Tummy exercises... now that's an interesting topic.
It's important to note that you cannot "spot reduce" an area of your body, doing sit-ups will not give you a slim stomach. The stomach is usually the first place to store fat, and the last place that fat disappears from. It's my belief that the body hangs onto the tummy fat as long as it can, as a defence against potential famine.
The only way to get a slim stomach is by increasing lean muscle mass and reducing overall body fat. I have found this to be true through experience, and there are also numerous reports that prove this fact.
I recommend that you forget about doing 100's of sit-ups, it's pointless. You would be far better off doing an overall body workout, at high intensity.
Doing the
Caveman Power 15 Minute Workout will get you toned, and it will burn fat and increase lean muscle mass. I guarantee that you will notice you're stomach getting tighter, but remember; it will probably be the last thing to feel tight - there's no way around that.
As for the fit-ball, it's an excellent tool for building your core strength and balance. I have a lot of exercises you can do using a fit-ball (I might make a video and post it on the website). Try kneeling on a fit-ball while lifting a weight or heavy ball above your head and behind your neck, this is excellent. I will try and get more examples to you shortly.
In summary;- Sit-ups are only for core strength, they do NOT give you a slim stomach.
- Overall body workouts that increase lean muscle and reduce body fat WILL give you a slim stomach.
- The fit-ball is for developing core strength and balance, and also helps when stretching.