You can find this exercise on page 57 of the book Synergistic Golf.
Exercise Type: STRENGTH
Exercise Category: BACK, LOW BACK, POSTURE, STRENGTH
Start face down on big ball with legs and arms straight out in front and back resting on the floor. Complete 10 repetitions lifting just arms and upper body off ball while legs form a stable base. Then repeat keeping hands or elbows on floor while legs lift in air initially engaging gluteals to start movement. Focus on balance and exhale on lift.