Angular velocity on the birthline with Ω_ini = 2.1 × 10^-5 s^-1 (value needed to obtain v_ZAMS/v_crit = 0.40 for the 14 M_⊙). Upper panel: angular velocity at the surface and in the centre of the star, along the birthline as a function of the total mass. Letters indicate the evolutionary stages described in the text (Sect. 3.1), and triangles indicate the appearance of the convective core. Lower panel: rotation profiles on the birthline at different masses from 2 M_⊙ to 14 M_⊙, by steps of 1 M_⊙.