You can find this exercise on page 117 of the book Synergistic Golf.
Exercise Type: PILATES
Exercise Category: BACK, POSTURE, SHOULDERS
Lie face down on floor with arms by sides and palms touching outer thighs. Inhale to prepare. As you exhale slide hands down legs and shoulder blades down back to bring upper body to slight extension. Hold throughout exhale. Legs should squeeze together, toes pointed and buttocks tight with belly button supporting low back. Inhale returning back to rest position on floor. Important: keep tops of feet on floor.