  The model analyzes the muscle fiber as a deformable system for which
experimental data are determinated with the help of the laws of Newtonian
mechanic. The model predicts the four transient phases for the shortening of a
muscle fiber according to a force or length step. The model shows, on the one
hand, the importance of the viscosity during the first phase of these two types
of step and, secondly, the interdependence of the six other phases towards a
bimodal state after disappearance of actions due to viscosity. The model
provides an interpretation for the behavior of a fiber with shortening
staircase. The model is consistent with experimental data during temperature
changes or various structural alterations.
