An article from Co.Exist
From the introduction on Co.Exists: "Physical exercise is good for your brain. And I mean really good for it. The brain burns a ton of energy during exercise, much more, even, than if you were thinking really hard about something really complicated. New research has discovered just what the brain does with all that extra energy.
"From a metabolic standpoint, vigorous exercise is the most demanding activity the brain encounters, much more intense than calculus or chess, but nobody knows what happens with all that energy," says the paper’s lead author Richard Maddock, of UC Davis.
One thing the brain is doing is building more neurotransmitters. In fact, it gets so busy doing this that brain fatigue might be the cause for endurance athletes hitting "the wall," and not physical exhaustion. "We often think of this point in terms of muscles being depleted of oxygen and energy molecules. But part of it may be that the brain has reached its limit," Maddock told the UC Davis Newsroom."