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.
Did all that holiday snacking leave you stretching the seams on your Santa suit? Coach Chris Bathke has what you need to get back into fighting shape, fast.