Running an entire marathon takes a lot of energy. Neuroscientist Carlos Matute knows this: he's run 18 of them. He wondered how runners' bodies get the energy they need to make it to the finish line. His new research in the journal Nature Metabolism may be the first step in answering the question – and suggests their brains might be (temporarily) depleting a fatty substance that coats nerve cells called myelin. Have other questions about the brain? Let us know by emailing shortwave@npr.org! Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.Learn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy