Modeling Mechanical Patterns for Striated Muscles

Muscles show a surprisingly large variety of functions when they mechanically respond to different environmental requests. However, the in vivo workloop studies distinguish well only four patterns of skeletal muscles, producing positive, negative, almost zero and zero net works, that qualifies them respectively as motors, brakes, struts, and springs. While much effort of comparative biologists has been done in searching for muscle design patterns, no fundamental concepts underlying such four primary patterns were established. In this interdisciplinary study, continuum mechanics is applied to the problem of muscle structure in relation to function. The known ability of a powering muscle as whole to be tuned via natural (resonant) frequency to the efficient locomotion is now modeled through the non-linear elastic muscle moduli, controlling both the contraction frequency and velocity. When incorporated in activated skeletal and cardiac (striated) muscles via the mechanical similarity between loaded and reaction forces, further exploration of elastic force patterns (borrowed from solid state physics) yields an explicit rationalization for currently known locomotor muscle patterns. Besides explanation of the origin of allometric exponents derived for leg muscles in animals adapted to fast running and wing muscles in flying birds, the skeletal and cardiac muscles are patterned through the primary and secondary high power activities. Further applications are expected to be useful in designing of artificial muscles and modeling living and extinct animals.