Sanford-Burnham researchers identify microRNAs as the missing link between the two defining features of muscle fitness—fuel-burning and fiber-type switching—providing a potential new target for interventions that boost fitness in people with chronic illness or injury.

Researchers discovered that small pieces of genetic material called microRNAs link the two defining characteristics of fit muscles: the ability to burn sugar and fat and the ability to switch between slow- and fast-twitch muscle fibers. The team used two complementary mouse models—the “marathon mouse” and the “couch potato mouse”—to make this discovery. But what’s more, they also found that active people have higher levels of one of these microRNAs than sedentary people. These findings, published May 8 in The Journal of Clinical Investigation, suggest microRNAs could be targeted for the development of new medical interventions aimed at improving muscle fitness in people with chronic illness or injury.

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