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Marathon runners use brain tissue as fuel, new study finds

Running long distances may be giving both your legs and your brain a workout

Runners running marathon in the city

Many runners rely on gels and sports drinks to help them power through a taxing marathon or ultra, but a new study suggests we may be using our brains to fuel us as well. Researchers discovered that marathon runners rely on myelin, the fatty tissue bundled around nerve fibres, for energy while racing. Here’s the rundown on the fascinating new findings.

Group of racers in trees

The study

Researchers from the Center for Co-operative Research in Biomaterials in San Sebastián, Spain, studied myelin levels in a group of city and mountain runners using MRI (magnetic resonance imaging) scans. They created maps of the myelin in participants’ brains before their races, within four hours of their marathon effort, and two weeks following their race, for comparison.

Directly after a marathon, the brain scans revealed that this brain tissue seemed to dwindle drastically. Within two weeks post-race, the brain fat bounces back to nearly pre-race levels. While carbohydrate is the still the main fuel source for athletes, the study suggested that brain tissue may also contribute: myelin use is a previously unknown form of “metabolic plasticity” that seems to maintain brain function during extreme conditions.

marathon runners on bridge

The takeaway

Runners working hard in a marathon will initially use all of their carbohydrate stores and then begin to use fat as fuel, eventually progressing to tapping into brain fat (myelin).

The work could have therapeutic implications, Sciencenews.org reported. An understanding of how runners’ myelin recovers so rapidly might offer clues for developing new treatments, potentially for people who’ve lost myelin due to aging or neurodegenerative disease. The team is now following the thread of their findings; they want to see if the runners’ myelin dip alters brain function, and how long it takes to recover completely.

The researchers are quick to point out that the results don’t mean that running is bad for the brain, and say that it’s possible that using and replenishing energy reserves is actually beneficial because it exercises the brain’s metabolic machinery. In other words, running long distances may be giving both your legs and your brain a workout.

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