Spot training is a myth, a widely known myth. Crunches do sorta give you a flat stomach, if you're going for a muscly flat stomach while also doing aerobic work outs. The only way to lose wieght in one place is to lose wieght over your entire body. So, instead of spending your time doing crunches to flatten the flab, try to run or walk for a while everyday. You'll lose wieght all over, including your stomach, then you can do those crunches to tone your stomach and give you a washboard!