Sit on floor with knees and hips bent. Hold medicine ball with both hands. Recline back slightly balancing on hips with bent legs positioned as counterbalance.
Touch ball on floor to one side by turning torso and reaching arms to same side. Touch ball to floor on other side by turning torso and reaching arms to opposite direction. Continue movement by rapidly moving ball from side to side.
Alternative form is to hold ball in front of chest with arms fully extended and parallel to thighs. Rotate upper body to each side, keeping arms in same plane. This alternative form prohibits the ball in making contact with floor at any point in movement. See Spot Reduction Myth.