It is generally believed that the main purpose of this practice is to increase the fat-burning capacity of the muscles, but most of the research on carb-restricted training has focused on a completely different benefit. That’s right: increased aerobic capacity.

I have been doing these kind of workouts for years.

You can’t, however, be afraid to back it back down by 20–30 percent the next week. By alternating your long runs back and forth between two distances you will be able to get more out of your body on that over-distance long run while not getting too close to the edge and going over.