How do the best endurance athletes partition their training? Most of understand what it is to go out for an easy run, but what about intervals. How do the best in the world do it? And, what does the science show about how you should design your interval workouts? What should you do for work duration, rest duration, total work, frequency, and effort level? These are the principle issues we discuss in this episode. And, we wrap up with parting advice from Dr. Seiler that you must hear if you're going to become your ultra best.