  The experimental finding of an ubiquitous kink in the nodal direction of
angle-resolved photoemission spectroscopies of superconducting cuprates has
been reproduced theoretically. Our model is built upon the Migdal-Eliashberg
theory for the electron self-energy within the phonon-coupling scenario.
Following this perturbative approach, a numerical evaluation of the bare band
dispersion energy in terms of the electron-phonon coupling parameter $\lambda$
allows a unified description of the nodal-kink effect. Our study reveals that
distinction between $\lambda$ and the technically defined mass-enhancement
parameter $\lambda^{*}$ is relevant for the quantitative description of data,
as well as for a meaningful interpretation of previous studies.
  A remarkable agreement between theory and experiment has been achieved for
different samples and at different doping levels. The full energy spectrum is
covered in the case of LSCO, Bi2212 and overdoped Y123. In the case of
underdoped Y123, the model applies to the low energy region (close to Fermi
level).
