Marathoners know it’s a mental sport — but it turns out their brains might be doing more than helping them power through the pain.
A new study found that during extreme endurance efforts like running a 26.2-mile race, the brain may temporarily break down its own insulation to use as an emergency energy source.
In plain English? It starts eating itself.
Emergency fuel
Myelin is a fatty substance that wraps around nerve fibers in the brain and spinal cord, much like insulation around an electrical wire. It speeds up and enhances nerve signal transmission, making it vital for everything from motor coordination to sensory processing.
During a marathon, runners primarily rely on carbohydrates — broken down into glucose — as their main energy source. But once those stores run dry, the body turns to fat reserves, including, as the study suggests, myelin in the brain.
Marathoners’ brains take a hit, but recover quickly
In the study, a team of researchers in Spain recruited 10 runners — eight male and two female — and performed MRI scans on their brains before and after a 42.2-kilometer race.
The results were striking: all runners showed a decrease in myelin levels, particularly in regions of the brain responsible for motor coordination, sensory integration and emotional processing.
But don’t toss those sneakers just yet. The study also found that the marathoners’ myelin began to bounce back shortly after the race and was back to normal levels within two months, indicating that the decline is both temporary and reversible.
“Myelin seems to act as an energy source when other brain nutrients are depleted during endurance exercise,” said Dr. Pedro Ramos-Cabrer, Ikerbasque research professor at CIC biomaGUNE, a nonprofit research organization in Spain.
“Further research is needed to establish how extreme exercise is related to the amount of myelin in the brain. Trials in a larger cohort are needed,” he added.
The authors also noted that the study didn’t assess whether the loss of myelin impacted the runners’ cognitive functions or physical abilities, so more research is needed in that area as well.
Breaking new ground
The study raises new questions about the role of myelin in the brain, not only in healthy individuals but also in those impacted by aging or disease.
“Understanding how the myelin in the runners recovers quickly may provide clues for developing treatments for demyelinating diseases, such as multiple sclerosis,” said Dr. Carlos Matute, professor of anatomy and human embryology at the University of the Basque Country.
In diseases like MS, the permanent loss of myelin — and the energy it provides — leads to severe brain damage and degeneration.
Myelin damage is also a key factor in amyotrophic lateral sclerosis (ALS). While regular, moderate-intensity physical activity is essential for maintaining brain health throughout life, research suggests that strenuous exercise can be a risk factor for the disease.
The study authors noted that regular endurance training might pose an additional risk for individuals with a genetic predisposition to ALS due to its potential to degrade myelin. However, they stressed that there is no immediate cause for concern and that further research is needed.
