A team of neurologists, neuroradiologists and biomaterials specialists affiliated with several institutions in Spain has found that marathon runners undergo a reversible reduction in myelin in the brain during a race. In their study published in the journal Nature Metabolism, the group analyzed MRI scans of marathon runners before and after a race and then at later intervals to learn more about how participating in long races impacts the brain.

The editors at the journal have published a Research Briefing that outlines the work in the same issue and suggest that the team’s findings could influence the understanding of brain metabolism.

The researchers recruited 10 runners—eight male and two female—and performed MRI scans of their brains before they ran a 42K marathon. They administered a second scan 24 to 48 hours later. Two of the runners received an MRI two weeks later, and six runners were scanned two months after the race as a follow-up.