You can find this exercise on page 163 of the book Synergistic Golf.
Exercise Type: PILATES
Exercise Category: FLEXIBILITY, HIPS, LEGS - FEET, POSTURE, STRENGTH
Lie on side with body hinged at hips approximately 10 degrees forward. All joints are stacked and feet are flexed. Top leg is slightly lifted up toward sky approximately 2 inches. Bottom arm is extended under ear and top arm is in front of chest with palm on floor for support. Inhale reaching top leg forward as far as possible with two pulses. Exhale kick same leg back with no pulse. Use momentum allowing the leg to stretch. Focus is on maintaining upper body and hips still and stable. Complete 8-10 kicks each side.