Unlike building muscle by targeting different muscle groups, such as abs or glutes, when you lose fat you lose it systemically — that means you lose it all over, not just in one place. Crunches may tighten the abdominal muscles, but those crunches won't specifically reduce your abdominal fat. The reason? Incompatible fuel. Fat cells store triglycerides. But when your body calls upon its energy reserves to be used as fuel, those triglycerides need to be converted into a fuel that your muscles are able to use — glycerol and fatty acids — and those can enter the bloodstream from anywhere fat is stored in the body, mid-section or otherwise [source: Perry].