Universe {#viscous-dynamics-in-the-isotropic-universe .unnumbered}
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We now focus our investigation in the opposite regime where the energy density takes a diverging value near the singularity. Then, let us consider the isotropic limit of the solution, leading to the flat Robertson-Walker Universe, by setting $q^2=0$ in the first integral (\[integrale2\]). The latter reduces to $$\label{integrale3}
\rho=\frac{1}{\chi}3H^{2}.$$ As a natural consequence of isotropy and compatibility issues with the Einstein equations, shear viscosity is not permitted in the model and bulk viscosity is the only retained contribution in the energy momentum expression (\[Tmunu\]). Indeed, in a homogeneous Universe, isotropically expanding, no friction between different layers can occur and the shear viscosity can affect inhomogeneous perturbations only. This set up has already been examined in [@BK_FRW] for an Eckart fluid via the dynamical system approach, and in [@Disc1] via the Lichnerowicz treatment in an attempt to explain dark-energy related current issues. Here we drew our attention to the behavior of the solutions in the limit of large density values. We address the problem by parameterizing $F$ according to expression (\[F\]) or, $$F=\frac{\gamma \rho R^3}{\mu_0},$$ where we have used the fact that $\mu=\mu_0 {R}^{-3}$ because of the rest-mass conservation law (\[restmass\]). It is easy to check 