In previous posts I’ve taken a critical look at the FASTER study (FASTER Again – Checking a number on Ben Greenfield’s data). In particular, I took at look at Ben Greenfield’s three hour data (FASTER10 – Ben Greenfield – Three Hour VO2 testing). Ben looked like he still had gas left in his tank after three hours of sub-maximal running.
But what about Damian Stoy (FASTER Subject 43)? He’s a vegan who is not at all fat fueled. He never got more fuel from fat than 50% and that was at 45% of his VO2max.
At 64% of VO2max, Damian was getting nearly zero of his energy from fat. His carbohydrate oxidation rate was ~10 kcal/min. So, in three hours of running, Damian burned ~1800 kcals which has to be close to his entire glycogen stores.
My conclusion? Beyond this time and intensity being carb fueled isn’t a great choice. The reason that marathons are 26 miles is historical and practical. People just can’t run hard for longer times.