You can find this exercise on page 160 of the book Synergistic Golf.
Exercise Type: PRE-ROUND WARMUP
Exercise Category: FLEXIBILITY, LOW BACK, RHYTHM - TIMING
Assume address position and-or golf ready stance with strong spine angle. Hold club parallel with ground with one hand on grip and other hand on hozzle. Keep head still and inhale rotating as if in backswing then exhale swinging the opposite way. Each direction may stay symmetrical keeping head still or mimic the asymmetric backswing and follow through. Repeat swings 10x each way.