While the basics of how a muscle generates power remain the same - that of filaments of myosin tugging on filaments of actin,causing them to contract the muscle - a new study reveals that strength doesn't just come from what's happening straight up and down the length of the muscle, as has been assumed for roughly half a century.
Instead, University of Washington-led research shows that as muscles bulge, the filaments are drawn apart from each other, causing the myosin to tug at sharper angles over greater distances. Ultimately, it's this action that deserves credit for half the change in muscle force scientists have been measuring, the researchers have found.
"The predominant thinking of the last 50 years is that 100 percent of the muscle force comes from changes as muscles shorten and myosin and actin filaments overlap. But when we isolated the effects of filament overlap we only got about half the change in force that physiologists know muscles are capable of producing," C. David Williams, who earned his doctorate at the UW while conducting the research, said in a press release.
The rest of the force, Williams explains, derives from the lattice work of filaments as it expands outward in bulging muscle.
In order to come to these realizations, Williams developed computer models to consider the geometry and physics at work on the filaments at a myriad of points.
"The ability to model in three dimensions and separate the effects of changes in lattice spacing from changes in muscle length wouldn't even have been possible without the advent of cloud computing in the last 10 years, because it takes ridiculous amounts of computational resources," he explained.
Furthermore, in addition to his co-authors, Williams validated the force trends using X-ray diffraction and moth flight muscle, which is very similar to human cardiac muscle.
"One of the major discoveries that David Williams brought to light is that force is generated in multiple directions, not just along the long axis of muscle as everyone thinks, but also in the radial direction," said Thomas Daniel, UW professor of biology and one of Williams' advisers and co-author on the paper. "This aspect of muscle force generation has flown under the radar for decades and is now becoming a critical feature of our understanding of normal and pathological aspects of muscle."
The work was supported with funding by the National Institutes of Health and National Science Foundation and with cloud computer access provided by an Amazon.com grant for research.