You can find this exercise on page 14 of the book Synergistic Golf.
Exercise Type: CARDIO
Exercise Category: CARDIO, LEGS - FEET, RHYTHM - TIMING
Start with hands on floor and one leg extended back in lunge position. Rapidly alternate feet jumping forward and back. Allow hips to go up and down in air as feet jump. Work quickly and generate power and momentum. Repeat 20-30x.