Oblique twist with medicine ball
Add some definition to your waist with the oblique twist with a medicine ball. Sit on the ground. Lean your torso back, and lift your legs off the ground, forming a "V" with your body. Holding a medicine ball in your hands, twist all the way to one side of your body before reversing the movement and twisting all the way to the other side. Perform 12 to 15 twists to each side.
Photo Credit: Girls Gone Sporty