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Massive stars can develop into tepid supergiants at several stages of theirpost main-sequence evolution, prior to core He-burning, on a blue loop, orclose to the final supernova explosion. We discuss observational constraints onmodels of massive star evolution obtained from the analysis of a sample ofGalactic supergiants and put them in the context of the cosmic abundancestandard as recently proposed from the study of their OB-type progenitors(Z=0.014 for stars in the solar neighbourhood). High-precision abundanceanalyses for He and CNO, with uncertainties as low as ~10-20%, trace thetransport efficiency of nuclear-processed material to the stellar surface,either by rotational mixing or during the first dredge-up. A mixing efficiencyhigher by a factor ~2 than predicted by current evolution models for rotatingstars is indicated, implying that additional effects need to be considered inevolutionary models like e.g. the interplay of circulation and magnetic fields.Blue loops are suggested to extend to higher masses and to higher Teff thanpredicted by the current generation of stellar evolution models.

Tepid Supergiants: Chemical Signatures of Stellar Evolution & The Extent of Blue Loops