Evolutionary tracks of massive stars during their core hydrogen burning evolution in the Hertzsprung-Russell diagram. For each selected initial mass (as labelled), tracks are shown for three different initial surface rotational velocities, ν_ZAMS = 0,400,500 km s^-1, in black, blue, and red, respectively. The time difference between two successive dots on each track is 10⁵ yr. The ZAMS is drawn as a green dashed line. The end of the tracks corresponds to the terminal age main sequence. The approximate location of the Humphreys-Davidson limit is indicated by the black dashed line (Humphreys & Davidson 1994).