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At the molecular level, muscle contracts when the molecular motor myosin binds to the filamentous protein actin. Single molecule techniques have allowed researchers to characterize, in exquisite detail, how a single myosin interacts with actin. But it is the combined effect of trillions of myosin motors that causes muscular contraction. As motors work together, they apply forces on each other and also deform the actin filament locally. These effects introduce coupling between the motors, so an isolated myosin molecule is not the same as a myosin molecule working in a group.

This coupling falls into two categories: 1) global coupling, where the attachment of one myosin affects all molecules equally; and 2) local coupling, where the attachment of one myosin only affects nearby molecules. We have developed partial differential equation models for both types of coupling. These models allow us to understand experimental results, including i) why groups of myosin move actin more rapidly than an isolated myosin, and ii) how an enigmatic muscle protein (myosin binding protein C) affects myosin's interaction with actin. This work gives insight into how the molecular scale affects macroscale muscle function, an important problem given the prevalence of genetic heart disease.