Mechanics of skeletal muscles

In contrast to inert matter, biological systems are characterized by structurally complex network architecture with domineering long range interactions. This leads, even in the absence of ATP, to highly unusual mechanical properties in both statics and dynamics. In this talk we discuss the simplest system of this type representing a segment of a muscle fiber and systematically study its peculiar thermodynamics and kinetics. Among the main macroscopic effects exhibited by our prototypical model are: the non-equivalence of soft and hard devices, the possibility of negative stiffness, coherent internal fluctuations at fixed loading and the presence of long living non-equilibrium steady states. Most intriguing, there is evidence that muscles are internally tuned to perform close to a critical point. We show that in the presence of a correlated noise, representing ATP, the system can generate active elasticity.