It’s All in the Fluid Dynamics

University of Michigan researchers have discovered that water flow within muscle fibers greatly influences their contraction rates, challenging traditional understandings of muscle mechanics and potentially improving artificial muscle design.

According to a study from the University of Michigan, the speed at which muscle fibers contract may be determined by the flow of water within them.

Nearly all animals use muscle to move, and it’s been known for a long time that muscle, like all other cells, is composed of about 70% water. But researchers don’t know what sets the range and upper limits of muscle performance. Previous research into how muscle works focused only on how it worked on a molecular level rather than how muscle fibers are shaped, that they are three-dimensional and are full of fluid.

U-M physicist Suraj Shankar together with L. Mahadevan, a professor of physics at Harvard University, created a theoretical model of water’s role in muscle contraction and found that how fluid moves through a muscle fiber determines how quickly a muscle fiber can contract.

They also found that muscle exhibits a new kind of elasticity called odd elasticity that allows muscle to generate power using three-dimensional deformations, shown in a common observation that when a muscle fiber contracts lengthwise, it also bulges perpendicularly.

Broader Implications and Applications

The researchers say this framework can be used to describe many other cells and tissues, which are also largely composed of water, and can be applied to the ultrafast movements of unicellular microorganisms and how they can be controlled. Their findings could also impact the design of soft actuators (a type of material that converts energy into motion), fast artificial muscles, and shape-morphing materials, all of which have very slow contraction speeds because they are triggered externally. Their results are published in the journal DOI: 10.1038/s41567-024-02540-x