You can find this exercise on page 41 of the book Synergistic Golf.
Exercise Type: TOWEL
Exercise Category: CHEST, FLEXIBILITY, LOW BACK, SHOULDERS
Stand tall holding towel from ends with both hands over head. Bend from elbows bringing towel parallel behind head at ear level. Slowly, try to straighten one arm out behind back then the other so arms hold towel behind hips. If possible, return each arm one at a time back up behind ears and return to start position. Try to complete 5 repetitions. Do not force the stretch.