You can find this exercise on page 128 of the book Synergistic Golf.
Exercise Type: YOGA-STRETCH
Exercise Category: ABDOMINALS, BALANCE, LOW BACK
Sit back behind sit bones (tailbone area). Pull belly button into spine for support and lift legs off floor. Body and legs should be in V position. Arms and legs are straight with arms reaching toward toes. Hold for 10 seconds. Repeat 3x. Maintain good posture keeping chin lifted and eyes forward.