Résumé
We review a construction based on an expansion around a (mass) fixed point renormalization group solution, in asymptotically free models. It transmutes the usual perturbative expansion of certain physical quantities in such a way that the alternative expansion parameter 1/F behaves like the ordinary coupling: Image in the perturbative regime Image, but like a power of Image in the infrared regime Image (Imagein and Λ being the scale invariant mass and basic scale respectively). (Borel) convergence of the induced series can hold in a range of F corresponding to reach unambiguously the strong coupling infrared regime, near Image. We argue that certain nonperturbative quantities, such as the (pole) mass gap typically, can be thus obtained from a direct resummation of this alternative expansion (i.e. without adding intrinsically nonperturbative power-like contributions).