With a partner, straddle and sit on a bench back to back with some space between. Place your feet flat on the floor. Hold a medicine ball with both hands.
You and your partner rotate torso to the same side. Hand the medicine ball to your partner. Now your partner holds the ball. Turn to the opposite side to again exchange the ball. Continue to rotate the ball to one direction. When finished, repeat with the opposite direction.
Start slow, gradually increasing the speed throughout the set.