Mechanics of Sarcomeres in Series and Instability - JURA Best Paper Award 2016-2017
Sarcomeres are the smallest independent unit of force production in the muscle. Current theoretical models of sarcomere in series, i.e. a myofibril, predict instability on the descending limb region of the force-length relationship. However, experimental evidence suggests that sarcomeres can be stable on the descending limb region with non-uniform lengths. The models presented re-evaluates the assumption that sarcomeres are independent units of contraction. Instead, it is hypothesized that there is a dependency between sarcomeres for force generation. Sarcomeres in series were modelled, with force as the dependent variable and sarcomere length and time as the independent variables. Models were developed with both independent and dependent sarcomere force generation. The independent sarcomere models resulted in instability that current theoretical models predict. Two cases of dependent sarcomere models were implemented, both included a shift in the passive force with varying degrees of dependency between adjacent sarcomeres. With these models, there was either stability with non-uniform length, stability with uniform length, or instability on the descending limb region of the force-length relationship. The major finding was that mathematically, sarcomeres with a variable passive force can reach equilibrium at various lengths if a dependency between adjacent sarcomeres is incorporated into the models.
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