Jillian Michaels: 6 Week Six-Pack $9.49

Having ripped abdominals may not make you a celebrity–well, unless you’re that guy on Jersey Shore–but if you’re looking to “lose weight, get healthy, and change your life,” as trainer Jillian Michaels puts it, then 6 Week Six-Pack should find a spot on your menu. It won’t be easy; there are two very challenging routines featured here, each of which should be practiced five days a week for three weeks. Nor will it be simply a matter of lying on the floor and doing a few sit-ups. Michaels’s mantra is “shed fat while toning your core,” and in the course of these two approximately 30-minute routines (Level 1 is hard; Level 2 is harder), you’ll spend a good amount of time on your feet doing vigorous aerobic work (marching in place, squats, lunges, leg lifts, and such, all designed to keep the heart rate up), as well as the demanding mat exercises, some of which derive from the plank (or upward pushup) position and thus build arm as well as core strength. The pace is quick, rests are few, and Michaels is a demanding instructor; there’s no coddling here, and the workouts are definitely not for the slothful or faint of heart. But she knows what she’s doing–her emphasis on the breath will be familiar to anyone who practices yoga, as will some of the poses she uses, and her attention to “control, focus, and form” is helpful. “Bring intention to your action,” Michaels says, and judging by the hundreds of positive user responses, it works. –Sam Graham