You can find this exercise on page 298 of the book Synergistic Golf.
Exercise Type: PILATES
Exercise Category: LEGS - FEET, RHYTHM - TIMING, STRENGTH
Lie on floor face down with upper body propped up on elbows and legs straight, squeezed together, toes pointed. Inhale to prepare. Exhale as one knee bends and pulses twice kicking heel toward buttocks. (First pulse: point, second pulse: flex foot) Inhale to return pointed foot back down. Repeat alternating legs. Complete 5-8 repetitions with each leg. Focus on maintaining spine angle and tightening hamstrings for power.