Sit on exercise ball. Walk forward on ball and lie back on ball with shoulders and head hanging off and knees and hips bent. Gently hyperextend back on contour of ball. Cross arms on chest.
Flex waist to raise upper torso. Return to original position. Repeat.
Movement can be made easier by positioning hips low on ball or placing arms further down to sides of waist. See Arm Position During Waist Exercises.
Exercise can be made more challenging by using positioning ball lower on back and hips higher or placing hands behind neck or beside head.