If you've been blasting through rep after rep of crunches, yet your abs are still M.I.A., it may be time to get off the floor and onto a treadmill.

In order for your six-pack to start popping, you have to reduce the amount of subcutaneous fat it's hiding behind. To do that, adding even more crunches to your ab workout really isn't the answer; while cutting back a bit on your caloric intake and ramping up your cardio workout should make all the difference. The first step in this process is to determine your body fat percentage. Then, use that information to tailor your proper ab-unveiling cardio workout. The following tips from Men's Health should help you along.

• If you have less than 15 percent body fat, do cardio 3 times a week. Results should show in one to two weeks.
• If you have 15-20 percent body fat, do cardio 3-4 times a week. Results should show in 2-3 weeks.

Source