Crunches won’t give you a flat stomach

At the end of the day, when people say they want a six-pack or a flat belly, what they really mean is they want to get rid of the layer of fat covering the muscles in their midsection. You can think of doing situps and crunches kind of like doing a bicep curl. Each type of exercise strengthens a specific group of muscles. And because both muscle groups are small, working them will not cause you to burn fat.

In order to lose fat, your body temperature must increase enough to trigger the metabolic effects necessary to burn fat. Using one small muscle group, such as the abdominals or the biceps, is not significant enough to create the amount of heat necessary for fat burning to begin. 

You can think about it like this: If the muscle group is small, the amount of heat it creates will also be small. To give you a better idea of how this process works, pretend the layer of fat you want to lose from your body is like wearing a jacket. If you were to do bicep curls or crunches, you probably wouldn't generate enough heat to make you want to remove the jacket.

Now imagine you perform full-body exercises such as running up hills, stairs or circuit training with the same jacket on. I think it's safe to say that after just a few minutes, you'll  want to rip that jacket (layer of fat) off. The reason the second type of exercise generates so much more heat than bicep curls or crunches is simply because they are high-intensity activities that use multiple muscle groups. 

This is why high-intensity, full-body exercises are more effective for fat loss than situps or crunches. The bottom line is that spot reduction is a myth, so you can save your money on all those gadgets, gizmos and workout plans being advertised. They don’t work. In order to have a flat belly, you have to reduce your total body fat percentage – and situps simply can’t do this.