Magnetic resonance imaging of 10 marathon runners revealed significant short-term reductions in myelin water fraction, a proxy for myelin, in key white matter regions immediately post-race. These changes recovered fully within two months. Researchers from the University of the Basque Country, including neuroscientist Carlos Matute, suggest myelin dynamics may reflect adaptive energy allocation during endurance exercise. The findings illuminate brain plasticity under metabolic stress without permanent structural damage, expanding understanding of neural adaptations to extreme physical activity.