“…Since the main interest of this paper is focused on the introduction of plasticity, in order to describe the contractile element we consider a simple sliding-filament model; other more sophisticated models (such as those introduced in [10], [12], [23], [25], and [27]) could be used without great additional difficulty. For the 3 same reasons we assume the muscle structures to be elastoplastic (with work hardening, i.e., the threshold separating two types of behavior can depend on the history of the deformation) instead of viscoelastoplastic, as may be more reasonable (see [11] for viscoelastic properties).…”