The intense physical demands of marathon running push the human body to its peak performance. The neural impact of long-distance running presents specific effects on brain tissue. Studies have shown marathon running reduces brain myelin levels temporarily before such changes can be restored. The scientific discovery about brain myelin reduction reveals new possibilities for brain research regarding exercise effects and neurological disorder studies.
Nerve fibers in the brain and spinal cord are protected by a coating made of a fatty substance called myelin. Brain signals rapidly pass through different regions of both brain and body because this protective substance exists in between brain areas. Damage or degradation of myelin tissue results in multiple neurological problems that may affect motor skills and mental functioning as well.
Runners were recruited from the Donostia City Marathon in 2022 (n = 2) and 2023 (n = 2). At the same time, two others competed in the Zegama-Aizkorri Mountain Marathon in 2023, along with two runners for the Hiru Handiak Mountain Marathon in the same year and two participants in the Valencia City Marathon. The participants received no payment for their volunteering services. Every subject in the study consisted of 8 men and 2 women who maintained good health status at the time of evaluation. They were all well-trained athletes between the ages of 45 and 73 years.
All participants provided their permission through written documentation before the study started to allow researchers to share any collected study data. The research team conducted studies under the standards of the Helsinki Declaration (2001) with approval from Comité de Ética de Investigación de Euskadi. The study included imaging procedures performed before and after the marathon within 24-48 hours of completion using MRI (n = 10) two weeks (n = 2) and two months (n = 6) after the race. The research did not need randomization because it studied only a single participant group. All participants in the study maintained good hydration status throughout the entire period.
The researchers next examined whether Myelin levels (MWF) levels recovered after rest following the endurance activity. To achieve this, they performed MRI scans on runners (n = 2) two weeks after the race. Although there was a significant partial rise in MWF values, they did not return to pre-run levels. This examines MWF at subsequent time points. The researchers found that two months post-marathon, MWF values were fully restored in all areas that had experienced a reduction. Therefore, myelinated tracts associated with both motor and non-motor functions returned to normal after two months of recovery from rigorous exercise.
The brain contains water that exists as CSF, extracellular and intracellular space and is also present between myelin layers, with a total mass composed of 70–85% water. The T2 relaxation time enables MRI to detect three water components in white matter. These include CSF as well as intracellular/extracellular water (LWF) and water present between MWF. Determining MWF involves analyzing short T2 components because it serves as the essential metric for myelin assessment. The combination of T2 mapping technology with the GRASE sequence allows myelin water imaging experiments to be completed in less than 10 minutes. The implementation of Myelin water imaging (MWI) remains difficult because MWF signals are both weak and brief.
The brain activation patterns after marathon running became clear through the study findings. Brain myelin content underwent a substantial decline during the first 24 hours following marathon completion, according to the obtained data. Researchers discovered myelin decreased throughout multiple brain parts, including those that support motor and cognitive processes.
For athletes, this research could provide valuable information about the impact of extreme physical activity on the brain. It also opens new areas of research for understanding how long-term endurance exercise might influence brain health and whether similar changes could occur in other forms of exercise.
The study’s outcomes demonstrate substantial results and provide valuable insights. The study indicates that running marathons causes short-term changes to brain myelin content, which will eventually return to normal levels. The brain demonstrated its capacity to restore myelin patterns back to its original state after running a marathon event through an observation period of thirty days. Researchers now have an opportunity to study how endurance-based physical activity impacts brain health and to determine if equivalent neural changes originate from different workout methods. The outcomes of this study trigger multiple questions regarding neurological effects on the body.
Future studies should examine possible links between short-term myelin degradation during stress and lasting mental disease pathology, as well as potential treatment for neurological conditions. The reduction of brain myelin, which marathon running causes, remains temporary since brain tissues return to normal levels throughout a month-long recovery period.
References: Ramos-Cabrer P, Cabrera-Zubizarreta A, Padro D, et al. Reversible reduction in brain myelin content upon marathon running. Nat Metab. 2025. doi:10.1038/s42255-025-01244-7
