Every so often, when your legs start to ache and the miles pile up, you’ve probably found yourself wondering how on earth you’re supposed to make it to the finish line—maybe after hours of running, with your energy reserves completely drained and your mind still sharp.
Carlos Matute is a neuroscientist. The kind who usually spends more time in the lab than on a running track. And yet, it was while running—during one of those long training sessions where your thoughts turn to liquid and your sense of self dissolves into the rhythmic beat of your shoes on the pavement—that he asked himself a seemingly simple question: how do we stay conscious all the way to the finish line when our energy is completely depleted?
From there, Matute did what any curious scientist does when they stumble onto a good question: he searched for an answer. And he found it in the most unexpected place of all—brain fat.
As National Geographic reports, in his study published in Nature Metabolism, Matute and his team showed that during extreme physical exertion—like running a marathon—the brain starts using its own myelin sheaths as fuel. These are the fatty layers that protect and insulate neurons. In essence, the brain feeds itself, temporarily sacrificing part of its own structure to stay alert.
The complex relationship between running and the brain
Some of the more sensational headlines claimed the brain “eats itself.” But the truth, as is often the case, is much more fascinating—and far less catastrophic.
The team conducted MRI scans on the brains of ten amateur runners before, after, and up to two months following a marathon. In the immediate aftermath, myelin levels were reduced in certain areas tied to movement, sensory perception, and emotional processing—unsurprisingly, the regions most activated during running. But within a few weeks, everything returned to normal.
This points to an extraordinary ability of the brain to adapt—even in brains that aren’t so young anymore: the participants ranged in age from 45 to 73. It’s a reminder that neuroplasticity doesn’t expire—it just evolves.
As Matute notes, this discovery once again shows just how astonishingly adaptable and dynamic our brain is, even in adulthood.
In other words, while you’re running yourself into exhaustion, your brain isn’t just holding on—it’s transforming. Levels of dopamine, serotonin, and endocannabinoids—the chemicals behind the famed “runner’s high”—all increase. Some studies have even observed enlargement of the hippocampus in marathon runners, the brain region linked to memory and learning.
The dark side of running: overtraining
But every form of growth comes at a cost. Pushing the body—and the brain—too far can lead to overtraining syndrome. It often starts subtly, with mood shifts before performance drops. Irritability, fatigue, a sense of disorientation: the exact opposite of what you’re chasing with your run.
In a study, Deakin University professor Luana Main and her team found that cognitive performance—especially reaction time—was impaired in athletes experiencing overload or overtraining. Main argues that when cognition is altered, people are more likely to make mistakes and get injured.
But that’s not a reason to stop. If anything, it’s a reason to learn to listen to yourself better. As Main suggests, subjective signals like mood and perceived stress are often more reliable than “objective” metrics when it comes to knowing if you’ve gone too far.
In short, your brain is far more than just a passenger on your run: it’s a lead player—adapting, changing, consuming, and rebuilding itself. As long as you treat it with respect.
When asked if running still makes sense, Matute replies calmly: “Yes, always. Just train smart.”