Kippenhahn diagram showing at what mass coordinates, m (y-axis), internal mixing regions arise, as well as the hydrogen mass fraction (color coded) as function of time for two 32 M_⊙ evolutionary sequences. One is computed with inefficient semiconvective mixing (α_sc = 0.01; top panel), and the other one is computed with efficient semiconvective mixing (α_sc = 100; bottom panel). The displayed time interval starts near core hydrogen exhaustion and ends in the early stage of core helium burning. The overshooting parameter for both models is α_ov = 0.33, and rotation is not included. Black dots indicate the mass coordinate of the maximum specific nuclear energy generation.