Trade the belly for a sculpted midsection in "The Biggest Loser" trainer Jillian Michaels's ab-shredding program, which replaces slowpoke sit-ups with a no-joke six-week regimen of burn-and-tone conditioning. Each 30-minute workout mixes core-focused cardio circuits and fat-zapping exercises, with warm-ups and cooldowns between; after three weeks at Level 1, the "Losing It with Jillian" host cranks the pressure with serious ab-toning.