You can find this exercise on page 110 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: BACK, FLEXIBILITY, LOW BACK
Stand with your feet firmly planted a little wider than hip distance apart extending ball in front of you shoulder height. Rotate 180 degrees facing behind you keeping ball straight out in front of you and maintain weight centered between both feet. Focus on lifting through the spine and be sure to lift your trailing heel for easier rotation. Repeat 5 times each direction.