You can find this exercise on page 35 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: HIPS, LEGS - FEET, LOW BACK, STRENGTH
Lie on floor with legs straight and heels on ball. Place hands on floor at sides. Squeeze gluteals, digging heels into ball and tilt pelvis off floor. Bend knees and pull ball into buttocks. Straighten legs slowly then lower hips. Keep abdominals tight and repeat 10 times. Advanced: try with arms in the air or try one leg at a time.