Most people who do abdominal crunches do them to get rid of the fat on top of the belly muscles. At our training center, in fact, we often get new members coming through the door complaining of a "weak core" when what they really have is fat on top of a perfectly strong set of muscles. If getting rid of the fat is the goal, there are better ways than crunches. A recent study from the University of Virginia showed that it takes 250,000 abdominal crunches to lose one pound of fat. That's about 700 daily crunches for a whole year. Compare that to a well-designed fat-loss plan, which usually results in a steady loss of one to three pounds per week, and you can see why crunches are a bad idea.
I love to bag on abdominal crunches. Hell, I'll even throw in leg lifts and those "side" crunches people do to get rid of the fat on the “sides” of their guts. Oh, and exercising in the fat-burning zone, that's another good one. Ahh...see that's it, isn't it. We're trying to find an easy way to get thin.