Left panel: surface velocity evolution during the MS for the 20 M_⊙ models at various metallicities. Right panel: radial component of the meridional circulation (U_r) inside the same models at the middle of the MS (X_c ≃ 0.35). Negative values of U_r mean that angular momentum is transported from the inner regions of the star to its outer parts, and a positive value corresponds to an angular momentum transport from the outer parts to the inner parts of the star.