Belly Blaster 1: Negative Sit-Up Start by sitting on the floor with your feet flat on the ground, knees bent and pointed toward the ceiling. Fold your arms in front of your chest. This is your starting position. Slowly roll back and lower yourself to the ground, one vertebra at a time. The toughest part will be the second half of the exercise, when your lower back is already on the ground and you're rolling the rest of your spine down. Return to starting position without using your hands.