You can find this exercise on page 268 of the book Synergistic Golf.
Exercise Type: HEAVY BALL
Exercise Category: HIPS, LEGS - FEET, POWER PRODUCTION, STRENGTH
Stand with feet together and gall in bent arms in front of chest. Lunge right foot forward dipping left knee toward floor. Outstretch arms diagonally over right knee bending forward to touch ball to floor on outside of foot. Push off front foot back to starting position. Ball then comes back to chest. Spine will round forward slightly during lunge, but focus on engaging abdominals to support joints.