A study involving MRI scans of marathon runners documented significant short-term decreases in myelin water fraction, a proxy for myelin content, in key white matter regions immediately post-race. These alterations normalized within two months, suggesting dynamic, reversible brain structural adaptations to endurance exercise. The research indicates that myelin, traditionally viewed as stable in adults, may serve as a transient energy reserve during high metabolic demand, providing new perspectives on brain plasticity and energy utilization.