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Ab belts may cause muscle contractions if used properly. But the belt alone cannot produce six-pack abs. The real challenge to ab definition is the layer of fat that lies right under the skin, hiding muscle tone.
You will perform this exercise as a variation on ab crunches. The difference is that you always have both feet off the ground during these bicycle crunches. This makes bicycle crunches a bit harder, than standard ab crunches. Also, it tends to work the lower abs more. Typically, keeping your legs off the ground works the lower abs. Keeping your legs flat, on the other hand, works the middle abs. Interestingly, bicycle crunches also work the rectus abdominus muscle (upper abs). This is the highest set of ab muscles you have.