You can find this exercise on page 38 of the book Synergistic Golf.
Exercise Type: PILATES
Exercise Category: ABDOMINALS, BALANCE, STRENGTH
Sit just back of your sit bones with knees flexed toward chest. Maintain balance with feet off the ground. Remain is C-curve and rock back and forth on spine. Inhale while rolling back one vertebrae at a time. Exhale while rocking spine back to seated position balancing behind sit bones constantly keeping the abdominals pulled in tight. Repeat 10 times.