Lay on top of exercise ball with legs and hands slightly apart. Place chest down so torso is wrapped over ball.
Raise left arm and torso upward beside head while raising right leg up behind body. Lower arm, torso, and leg to original position and repeat. Repeat by raising and lowering right arm and left leg in same manner. Repeat by alternating between opposite sides.
Lift leg and arm deliberately with no jerking. Also see Bird Dog (on exercise ball).
Movement can be made easier by positioning body a bit lower on ball.
Exercise can be made more challenging by positioning ball lower toward hips or place supporting arm further away from ball.