You can find this exercise on page 119 of the book Synergistic Golf.
Exercise Type: HEAVY BALL
Exercise Category: ABDOMINALS, LOW BACK, POWER PRODUCTION, STRENGTH
Lie down on back holding ball on chest with legs straight together and toes pointed. Inhale to prepare. Exhale as you roll up halfway turning upper body toward the left as left leg bends and lifts toward chest. Goal is to touch right elbow to left knee. Inhale returning body to flat and exhale repeat on other side. 20 repetitions total. Focus on rounding spine on the way up and on the way down with control.