  We revisit the standard procedure to match non-perturbative models to
perturbative QCD, using experimental data. The strong coupling constant plays a
central role in the QCD evolution of parton densities. We will extend this
procedure with a non-perturbative generalization of the QCD running coupling
and use this new development to understand why perturbative treatments are
working reasonably well in the context of hadronic models. Vice versa, this new
procedure broadens the ways of analyzing the freezing of the running coupling
constant.
