You can find this exercise on page 185 of the book Synergistic Golf.
Exercise Type: DYNAMIC STRETCH
Exercise Category: BACK, FLEXIBILITY
Stand with feet a little wider than hips. Arms over head with hands clasped together. Inhale to prepare. Exhale as arms reach forward pulling shoulders forward and rounding back. Tuck hips under to emphasize full flexion of spine. Breathe throughout and hold for 10 seconds. Repeat 2x.