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.
For several years, I was the Watson to Strength Coach Charles Poliquin's Sherlock Holmes. I chronicled his theories, revelations and discoveries. I like to think I played a small part in his success but in all probability, guys like Charles don't need any help; they get famous all on their own.