Meeting Abstract
Muscle is active, regulated soft matter, hierarchically organized into a structure that has unique material properties, particularly regarding its instantaneous stiffness. Prior experimental work used dynamic testing to characterize the complex modulus of active muscle for fully activated isolated muscle fibers. This modulus measures the component of stress that is in phase with periodic length changes (elastic component) as well as the out-of-phase component (viscous component). The complex modulus for active muscle shows a highly non-monotonic behavior with increasing frequency of applied length change. Its Nyquist plot shows a cardioid shape as frequency increases. In contrast, both passive and rigor muscle shows very simple increases in stiffness with increasing frequencies, consistent with passive visco-elastic materials. We used a spatially explicit half sarcomere model to simulate muscle’s dynamic force in response to applied sinusoidal length changes. In particular, we asked how well the model reproduces the material properties of skeletal muscle that have been previously measured. Our model is a stochastic simulation based upon a coupled elastic model of myosin motors, thick and thin filament mechanics, including titin mechanics and overall lattice spacing. We simulated force in response to applied sinusoidal length changes ranging from 4.3 to 100 Hz and found that our model reproduces the cardiod-like Nyquist plots seen in similar in vitro experiments. Using a computational model we show the emergence of muscle’s unique macroscopic dynamics and material properties from microscopic principles.
