When Jillian Michaels says "you can lose up to 20 pounds in 30 days" by following her 20-minute-a-day workout, believe her. There's a reason her 30 Day Shred workout has become a national hit: it works. But anyone who's ever seen Michaels work out with contestants on The Biggest Loser knows it's not necessarily going to be easy. The 30 Day Shred features three 20-minute workouts, each of which features, in rapid succession, short bursts of strength, cardio, and abs, and a cool-down. Sound easy? Think again. Even the beginner-level workout will have users' heart rates up. Michaels allows no resting between each short burst of exercise, which is part of why the results happen so quickly.

The transitions between strength, which can feature classic moves like pushups or reps with small weights, and cardio, and then between cardio and abs, are a mere second or two. But that pacing helps guarantee the results that Michaels touts. "This helps you burn more fat and more calories, and gets you toned that much faster," Michaels exhorts as she zips through the exercises. There are a few modified moves for true beginners, but even for them, Michaels doesn't cut much slack; everyone has to do real jumping jacks, and a lot of them. "I have 400-pound people who can do jumping jacks," Michaels says "and if they can do it, you can do it!" The only thing you need to jump into the 30 Day Shred is a set of small hand weights, and, if you have a hard floor, a mat for the floor moves. Otherwise, commit 20 minutes a day for a month, and get that lean, shredded body you've always wanted