If you've been diligently doing an ab routine to get strong and swimsuit-ready, chances are that your efforts have paid off and it's time to up the ante with a more advanced program--something to get you a seriously sculpted midsection. The good news: Improving your results doesn't mean you'll have to increase your workout time. In fact, with this resistance-based Rx from exercise physiologist and certified trainer Scott McLain, you might even get better results by doing less.

With his program, you use external resistance (such as a medicine ball or dumbbell) to exhaust your ab muscles in no more than 15 reps per set. "The abs are like any other muscles in the body," explains McLain, personal training manager at Westerville Athletic Club in Columbus, Ohio. "To get stronger, you need to work them to the point of fatigue. Adding resistance is a quick, effective way to do that."

McLain's cutting-edge exercises are designed to work all four abdominal muscles and your spine extensors for a complete core workout. We've also included instructions for beginners as well as advanced exercisers, so it's great for any fitness level. With the time you save by performing fewer reps, McLain recommends doing extra cardio to melt ab flab. And if you watch your diet (see "The Flat Abs Diet"), in just six to eight weeks you could be bellying up to the extra-firm, extra-flat, extraordinary abs you're after.