On November 5, the 52nd annual New York City Marathon took place with over 50,000 runners crossing the finish line. The fastest marathon runners ran 26.2 miles in just over two hours. To the average person, this speed and distance may be astonishing, and to scientists marathon running has sparked some interesting observations.
In a recent preliminary study, scientists are finding that in many endurance athletes, some of their energy sources may be coming from an unexpected source: brain tissue.
It appears that marathon runners rely on myelin, a fatty tissue that surrounds nerve cells, as energy during a race. The human brain contains an abundance of myelin as the insulation allows electrical signals to pass from cell to cell, which is crucial for brain function.
“The fatty tissue seems to be a straightforward material with a straightforward job, but there’s likely more to it than that”, says Klaus-Armin Nave, a neurobiologist at the Max Planck Institute for Multidisciplinary Sciences in Göttingen, Germany. “For the longest time, it was thought that myelin sheaths were assembled, inert structures of insulation that don’t change much after they’re made,” he says. However, MRI scans are showing that myelin is a dynamic and adaptable tissue that is not only available to the body as a reserve energy source during prolonged physical exercise, but also as a replenishable source of fuel.
The body eats at the myelin for fuel, and in the day or two after the marathon, the tissue is almost depleted. However, two weeks after the race, the brain tissue returns back to pre-race levels. Carlos Matute, a neurobiologist at the Achucarro Basque Center for Neuroscience and the University of the Basque Country in Leioa, Spain, wanted to determine if myelin fats could sustain the brain of endurance athletes while they were running. Using an MRI, his team scanned the brains of four marathon runners before and after their race. Their finding showed that marathon runners underwent significant myelin depletion. The reduction involves both white and gray matter in the brain, as well as the primary motor and sensory cortical areas and pathways in the brain. These results revealed that myelin use and replenishment is an extraordinary form of metabolic plasticity, an ability that allows cells to adapt their specific needs in response to various stimuli.
Matute and his team are now putting together the pieces of their findings. They are looking to determine whether the loss of myelin that occurs during running alters brain function, and how long it takes for brain tissue to regenerate completely.
As a marathon runner himself, Matute emphasizes that his results do not mean running is bad for the brain. “Not at all,” he says. It is possible that the depletion and regeneration of energy and brain tissue is beneficial to the brain’s metabolic capability.
Some scientists also suggest that athletes burn so much energy running that they need to tap into new fuel supplies in order to keep their brains operating. “This is definitely an intriguing observation,” says Mustapha Bouhrara, a neuroimaging scientist at the National Institute on Aging in Baltimore. “It is quite plausible that myelin lipids are used as fuel in extended exercise.”
More studies and testing are required in order to ensure the validity of these preliminary studies. However, if what scientists are seeing is further supported, this information could be used for therapeutic purposes. Understanding how runners are able to recover their myelin so rapidly may offer insights into developing potential treatments for myelin loss due to aging or neurodegenerative disease.
