Does a marathon damage the brain?
The constant exertion wears down the nerve cells: The myelin sheaths become thinner in some regions of the brain during a marathon run. Regeneration takes weeks.
According to a study published in the journal "Nature Metabolism", certain regions of the brain lose myelin - the insulating wrapping around the nerve processes that enables faster transmission of stimuli - during a marathon run. Two months after the run, however, the myelin layers had fully regenerated. The research team led by Carlos Matute from the University of the Basque Country assumes that the breakdown of lipid-rich myelin membranes during peak physical exertion provides the brain with much-needed energy.
The Spanish researchers used a special variant of magnetic resonance imaging to examine the brains of ten marathon runners before and up to two days after the 42-kilometre run. The method records the myelin content by measuring its water content. In the eight men and two women, the working group discovered a reduction in myelin content in several areas of the brain, including those that control and coordinate movement. After two weeks, myelination in the affected brain regions had increased significantly again and reached the initial level when measured again two months after the run.
Dehydration unlikely to be the cause
The authors consider it unlikely that the measurement results reflect localised dehydration of the brain, especially as the effect was still visible two days after the marathon. Rather, they suspect that myelin serves as an energy reserve for the brain during extreme endurance exercise, as it consists of around 70 per cent lipid molecules. Similar to fat in the body, these are possibly metabolised to generate energy as soon as the glycogen reserves in the brain are used up. Glycogen is a multiple sugar that serves as an energy store in the animal organism. Whether the temporary loss of myelin after a marathon damages the neurons and whether this leads to losses in brain function remains an open question. In any case, the degradation was limited and most of the myelin appeared untouched, the authors emphasise.
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