You can find this exercise on page 34 of the book Synergistic Golf.
Exercise Type: YOGA-STRETCH
Exercise Category: BACK, BALANCE, LOW BACK, POSTURE
On hands and knees, keep your back flat and abdominals supporting spine. Lengthen your left leg behind you while squeezing the gluteal. When you feel balanced. Lengthen the right arm in front of you. You want your extended arms, legs, and spine to be horizontal to the floor. Hold up to 30 seconds. Focus on your breathing and relaxation.