Hertzsprung-Russell diagram of a 10 M_⊙ model with low MS core overshooting, illustrating a blue loop contraction episode. The lines and coloured symbols have the same meaning as in Figs. 1 and 2. An additional term W_nuc,m is subtracted to assess stability during the blue loop phase. Roughly three-quarters of the way through core-He burning as an RSG, the model undergoes a blue loop, initially moving away from thermal balance before regaining stability and continuing as a BSG.