Running 26.2 miles may not be everyone’s idea of a good time — but marathon running is booming, with participation surging at races around the world. And while hours of cardio certainly take a toll on the body, new research published in Nature Metabolism suggests that our brains may help with some of the heavy lifting. Read on for more information about the culprit behind “marathon brain.”
Small Study Examines Marathon Brain Impacts
To function during a marathon or any other feat of endurance, our bodies rely on stored carbohydrates for fuel. However, this fuel inevitably runs low as activity continues. At that point, our bodies rely on stored fat. The new research published in Nature Metabolism suggests that myelin — the protective membrane around the nerve fibers in the brain and spinal cord — may be an unexpected emergency source of fat. But how long does it take marathon runners to return to normal myelin levels?
Myelin Loss in Marathon Runners
The team built on previous research, which suggested that rodents’ brains could use myelin as a fat source. This is no surprise given that the protective myelin membrane is primarily made up of lipids. The new research focused on human subjects, asking marathon runners to undergo magnetic resonance imaging (MRI) scans up to two days before a scheduled race. The runners were then given follow-up MRIs a day or two after the run. Some runners also received scans weeks or months later. The team post-processed the MRI sequences with the DECAES algorithm, which provided three-dimensional parametric maps of the myelin water fraction within each runner’s brain.
Before the marathon, the runners all had similar levels of myelin. After their races, the participants all exhibited “substantial” decreases in myelin; specifically, the runners exhibited reduced myelin in brain regions involved with both motor coordination and sensory integration. To pinpoint the affected brain regions, the researchers divided the brain scans into 50 white matter regions using the JHU brain atlas of white matter tracks. They also divided the scans into 56 grey matter regions using the LPBA40 collection of the SRI24 brain atlas.
Possibilities for Future Research
Ultimately, the team found that marathon runners had significantly reduced myelin levels after extreme activity. Additionally, for some runners, it took two months or more for their myelin levels to return to their pre-marathon baseline.
From their findings, the researchers deduced that brain myelin content is “temporarily and reversibly diminished by severe exercise,” with myelin lipids seeming to serve as an energy reserve. They also noted one factor that remains unclear: whether myelin is used differently depending on the emergency situation. For example, marathon runners may rely on myelin during prolonged periods of running, but would someone undergoing a different kind of chronic stress use it in the same way?
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Given the small sample size associated with these findings, further research is necessary. However, the findings may prove useful as scientists attempt to understand potential long-term implications of myelin loss, particularly as it pertains to neurodegenerative disorders.
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