The hip roll is great if you are looking to target the midsection. This exercise is used to target the oblique muscles, which occupy the sides of the midsection. The job of the obliques is to assist with rotation of the torso, as well as basic abdominal contractions.
The hip roll is done from the supine position (on your back) with the hands out to the sides and palms face down. Bend the knees and keep the feet together on the floor. The knees should also be close together at all times. Lower both knees to one side of the floor just short of touching the ground, then slowly repeat the movement on the opposite side. The knees should travel back and forth in a straight, 180-degree line. Keep the abs "sucked in" and the chest high during the hip roll exercise.
Lie down with back flat. Arms out with palms face down.
Bend the knees, then lower them to one side. Abs "sucked in" tight.
Alternate the movement on each side.