That is their assumption, but I'm not sure they really can say that. I notice that they didn't measure cortisol, which seems odd. When you exercise, the increa

That is their assumption, but I'm not sure they really can say that. I notice that they didn't measure cortisol, which seems odd. When you exercise, the increase in cortisol results in a 50% increase in endurance compared to if there was no cortisol increase, at least in rat experiments [1]. Given that cortisol is involved in both mental alertness and physical endurance, it seems like it could be a plausible reason for this finding. 1. https://www.researchgate.net/profile/Mehis_Viru/publication/8367555_Cortisol--essential_adaptation_hormone_in_exercise/links/5448da0d0cf22b3c14e336b4.pdf https://www.researchgate.net/profile/Mehis_Viru/publication/...