You can find this exercise on page 197 of the book Synergistic Golf.
Exercise Type: YOGA-STRETCH
Exercise Category: ABDOMINALS, POSTURE
Sit tall with straight back and legs extended together in front of body. Lift right foot and rest right heel on top of left toes. Inhale lifting spine as arms extend in front of chest. Exhale hinging from hips reaching hands to toes. Inhale back to start and repeat movement 5x. Switch legs.