For this exercise you will need a medicine ball and a partner. Stand back to back with your partner, spaced 2-3 feet apart. This will be your starting position. Hold the ball in front of the trunk. Open the hips and turn the shoulders at the same time as your partner. For full rotation, you and your partner should twist in the same direction, i.e. counter-clockwise. Pass the ball to your partner, and both of you can now twist in the opposite direction to repeat the procedure.