Scientists discover rare superfast muscles in mouse legs

You might think that only DC Comics superhero The Flash could run at a speed of 200 strides per second. But in the animal world, special muscles—called "superfast muscles"—can move as fast as Barry Allen.

Now, for the first time, scientists from the Institute of Zoology and the Beijing Institute of Stem Cells and Regenerative Medicine of the Chinese Academy of Sciences have identified these muscles in mouse legs, raising the prospect of future research that could break the physical speed limits of normal human arm and leg movements.

Traditionally, superfast muscles have only been found in some obscure parts of animal anatomy including hummingbird wings, rattlesnake tails, and bat larynxes. While fast twitch muscles—the muscles that athletes use for activities like sprinting—are widespread in mammalian limbs, superfast muscles had previously only been identified in one part of human and mammalian anatomy: the extraocular muscles that control rapid eye movement.

"We achieved this feat by optimizing a new technology called single-cell metabolomic imaging," said Prof. Ng Shyh Chang, senior author of the study.

The researchers used this new technology to study cells in frozen slices of mouse leg muscles. They found that some of these cells contained metabolic signatures, i.e., groups of biochemicals produced during cell metabolism, that are normally found only in superfast muscles.

The superfast cells in the mouse legs, which showed a large amount of metabolites and genes associated with physical training, also contained metabolic signatures resembling those of oxidative muscles—i.e., fatigue-resistant muscles used for endurance exercise like marathons.

The scientists hypothesized that, with repeated neural stimulation, the mouse legs had begun to form small numbers of superfast muscles similar to those that control human eye movements.

With this knowledge, scientists may be able to unlock a wide range of therapeutic interventions that push the physical boundaries of what human limbs can achieve.