Exercise ball, fitball or Swiss ball -- they're all essentially the same thing -- a big inflated ball that you can use to do body exercises on.

A "crunch" is an exercise for the abdominal muscles of the stomach area. This involves lying on the back and lifting the back and shoulders off the ground while tightening the abdominal muscles.

You can also do this on a fitness ball. The advantages are that the slight instability requires that you recruit the side muscles called the "obliques" as well, and that the ball instability provides a more lateral working of the whole abdominal area. It is proven as one of the best exercises for the abdominals.

---> How to Do the Fitball Crunch

More reading:

• How to Train the Abdominal Muscles
• Most Effective Abs Exercises