Start standing with feet shoulder-width apart, holding a dumbbell in each hand at waist level, palms facing you. Keeping back flat and engaging your ab muscles, bend from the hips and slowly lower weights toward the floor, keeping them close to your body, while simultaneously lifting left leg behind you. Stop when your chest is parallel to the floor. Hold for one second, then return to standing. That's 1 rep. Repeat for 10 to 12 reps, then switch legs.