You can find this exercise on page 32 of the book Synergistic Golf.
Exercise Type: DB STRENGTH
Exercise Category: BACK, POSTURE, SHOULDERS, STRENGTH
Stand with feet slightly wider than hips. Unlock knees and hinge from waist so back is flat and parallel with floor. Arms are hanging straight down from chest holding 3-5-8lb dumbbells facing each other. Inhale prepare. Exhale lifting and flying dumbbells out to sides so arms spread like wings parallel to floor. Inhale as arms slowly return to start. Focus on strong back and good posture. Abdominals held in to support back. Repeat 10-15 repetitions.