You can find this exercise on page 154 of the book Synergistic Golf.
Exercise Type: DB STRENGTH
Exercise Category: BACK, SHOULDERS, STRENGTH
Stand with feet hip distance apart holding three 5 to 8lb dumbbells in hands with palms facing front of thighs. Inhale to prepare with focus on strong stance and posture. Exhale lifting both arms straight forward to shoulder height and width. Inhale return hands to thighs. Repeat lifting sequence 10-20x. If weights get too heavy, lift one arm at a time. Do not allow body to sway or move during exercise.