It is well known that XC ski racers have to be incredibly “fit” to be competitive. But how do we measure “fitness”? For decades, we’ve known that a high VO2max is necessary to be a competitive ski racer. Training to improve VO2max involves a large volume of training at a low intensity and a comparatively smaller volume of training at a very high intensity. Over the past 20 years, changes in equipment technology, course preparation,...