The change was apparent on the molecular level as well, when Khurana and colleagues analyzed a type of leg muscle that is typically dominated by easily fatigued, "fast-twitch" fibers. In these mice, the muscles had been reprogrammed to resemble the high-endurance, slow-twitch variety, he said.
It is unclear just how the findings, published online this month in the Journal of Clinical Investigation, might translate to people. Still, there are intriguing clues:
In addition to the mouse analysis, the researchers studied the same gene in human endurance athletes, including cyclists and swimmers. Unlike the mice, these athletes were not missing the gene, but they were more likely to have one of several specific variants. That suggests the gene is somehow involved in human muscle endurance, though further study is needed, said Emidio E. Pistilli, who collaborated with Khurana as a postdoctoral fellow.
"We feel like there's something there," said Pistilli, now an assistant professor at the West Virginia University School of Medicine.
Khurana said the results might help in the study of muscular dystrophy and also obesity - a condition for which it would be useful to boost the amount of fatigue-resistant muscle.
He acknowledged that such research also draws the interest of professional athletes seeking to gain an unfair edge. After a previous study on a protein that was linked to muscle growth, for example, Khurana was dismayed - though not surprised - to receive just as many inquiries from athletes as he did from patients.
"Athletes need very little encouragement for trying the latest fad," said Khurana, a professor of physiology at Penn's Perelman School of Medicine. (Concerned about such abuse, he also has done research for the World Anti-Doping Agency.)
