These are rapid back-and-forth shuttles with one step in between direction changes. Go two steps to the right, then two to the left.
This really focuses on lateral change of direction, and it's a great way to improve coordination and leg strength/power while building structural integrity in the lower body. Higher reps will scorch your quads and lungs.
Scot Abel is a bodybuilding anarchist. He doesn't believe in tempo training, pre-determined rest intervals, back-off weeks, or the fact we have elves in the basement that make Metabolic Drive. What he does believe in is pretty cool, though.