The paper deals with the dynamical analysis of the system of first-order ODE’s describing the isometric stimulation of the muscle fibre. This system is considered to be a non-autonomous one having the periodical excitation. For the analysis of dynamical behaviour the system the multiple scale method (MSM) is employed. The main goal of this contribution is to show the application of MSM to the non-autonomous dynamical system using the first order approximation of the solution. The existence of the degenerated Hopf’s bifurcation of the gained solution is presented