You can find this exercise on page 215 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: HIPS, LOW BACK, STRENGTH
Lie on floor with legs straight out and toes pointed just barely on the ball. Abdominals engaged at all times. Squeeze glutes while pushing toes into ball pulsing hips off the floor. Complete 20-25 repetitions maintaining neutral spine.