Improvement of the muscle fractional multimodel for low-rate stimulation

Modeling of isometric contractions, due to motor unit (MU) stimulations of Peroneus digiti quarti and peroneus brevis rat muscles, is presented. The modeling is realized through a multimodel, which allows distinguishing asymmetric contractions and relaxation mechanisms for time domain identification. First, this paper compares two fractional functions and a rational transfer function that model each phase of IIA and IIB MU twitch. The advantages of using fractional functions are underlined, since the number of parameters are minimized. Indeed, fractional models, due to its infinite dimension nature, are particularly adapted not only to model complex systems with few parameters but also to obtain a real time exploitable model for a salamander robot simulator. Finally, muscle response for 10 Hz pulse stimulation shows non-stationary characteristics. A method, modeling the transient state of muscle responses and introducing time varying parameters, is presented.