The ability to complete a long-duration, high-energy-expenditure run without caloric intake is termed 'fad adaptation' and relies on tapping into various energy stores beyond glycogen.

“so in the parlance that's that's what we call fad adaptation because you know if you do the math it the extent to which you're expending energy or you're probably expending somewhere in the neighborhood of six to seven hundred kilojoules per hour and you know if you were trying to get access to that just from glycogen I mean you'd be done in probably two three hours two or three you know two or three at most and I was fairly aggressive pace right so you know there's a series of energy stores that you tap into depending on your output and duration you know that well”