Study investigates how running a marathon impacts brain health

Marathoners hear plenty of scary claims about what running 26.2 miles can do to the brain. A new open access study paints a clearer, calmer picture.

Exercise research over the past two decades has consistently linked regular activity with sharper attention, memory, and learning.

This foundational review summarizes how aerobic training supports brain networks and key molecular pathways that help the brain adapt.

Brains, myelin, and marathons

The work was led by Carlos Matute, professor of neurosciences at the University of the Basque Country (EUH).

Researchers scanned 10 runners ages 45 to 73 with advanced MRI both 24 to 48 hours before and after a marathon, then again for subsets at two weeks and two months.

They focused on myelin water fraction (MWF), an MRI signal that tracks water trapped within the myelin layers that insulate nerve fibers.

MWF is widely used as an in vivo marker for myelin content, with good agreement to tissue studies. It is sensitive to subtle shifts that may not show up on standard brain scans.

The team found significant reductions in MWF across 12 white matter regions that carry movement and sensory signals.

The largest drops reached 28 percent in the pontine crossing tracts and 26 percent in the corticospinal tracts, all reported without changes in overall brain volume or hydration patterns.

Why myelin dropped after 26.2 miles

“We define this process as metabolic myelin plasticity,” wrote Matute. The authors argue the brain turns to myelin lipids for energy when glucose dips during a long race. 

This proposal builds on animal work showing oligodendrocytes can support neurons by mobilizing fatty acids during metabolic stress. It also fits basic chemistry, since myelin is 70 to 80 percent lipid by composition.

Importantly, the signal changes were regional, not global, which argues against a simple dehydration effect.

The study also reports no change in total brain or tissue compartment volumes, which strengthens that interpretation.

Does less myelin mean worse thinking

This study did not track cognition. It documents a short term shift in a myelin sensitive MRI signal after a marathon.

Context matters here. Most human data still show that regular physical activity supports attention, processing speed, and memory across the lifespan.

That background helps frame a temporary signal dip as an adaptation to energy demand, not as damage.

The authors interpret the pattern as a transient physiological response that rebalances with rest. That stance aligns with what we know about adult myelin turnover and repair.

Brain rebound time after marathons

Two weeks after the race, MWF levels had risen substantially in the scanned participants, though not yet back to baseline.

By two months, MWF values matched pre-race levels across the regions that had dipped.

That timeline maps onto known myelin remodeling dynamics in adults and speaks to the brain’s ability to restore insulation after a metabolic push.

The recovery also matters for safety. A transient change that resolves within weeks belongs in a different category than injuries that accumulate or persist.

Who was studied and what that means

The sample was small and skewed older, and it mixed city and mountain events. Those features limit how far we can generalize to younger runners or ultradistance athletes.

MWF is semiquantitative and, like any imaging metric, can be influenced by technical factors and local tissue context.

That is why the paper emphasizes region specific effects, stable brain volumes, and the need for replication with larger cohorts that include cognitive and physiological testing.

The authors note that trials with more runners and richer measurements will be crucial to probe individual differences. That includes training history, recovery routines, and health status.

Marathons and future brain health

The study did not test whether in race fueling strategies, pacing, or race conditions change the depth or duration of MWF dips. Those remain open questions that future work can address directly.

“Running marathons is not harmful for the brain; on the contrary, the use and replacement of myelin as an energy reserve is beneficial because this exercises the brain’s metabolic machinery,” said Matute.

A reliable, reversible stress on myelin could help scientists test ideas about how quickly the adult brain can rebuild insulation. That may eventually inform research on demyelinating conditions where repair falls behind need.

Nothing here suggests runners should avoid marathons for brain reasons. The data support a story of metabolic flexibility, with insulation temporarily tapped to keep signals flowing when energy gets tight, then restored after the effort.

The study is published in Nature Metabolism.

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