Profiles of hydrogen (in mass fraction, dotted lines) and of helium (solid lines) as a function of the Lagrangian mass coordinate inside a 15   M_⊙ model at Z = 0.002 with V_ini/V_crit = 0.50 for different prescriptions for the D_shear (blue: M97; red: TZ97. Left: profiles in the last third of the MS phase. Right: just after the MS phase, when . The shaded areas represent the extension of the convective zone associated to the H-burning shell (dark grey: M97 model; light grey: TZ97 model).