2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/82579We discuss the effects of fast nuclear excitations on heavy-ion fusion reactions at energies near and below the Coulomb barrier. Using the fusion of two $^{40}$Ca nuclei as an example and the inversion method, we show that the mass renormalization induced by fast nuclear excitations leads to a large surface diffuseness in the effective potential for heavy-ion fusion reactions.13 pages, LatexNuclear Theorytext