We extend the PARSEC library of stellar evolutionary tracks by computing new models of massive stars , from 14 { ~ { } M _ { \odot } } to 350 { ~ { } M _ { \odot } } .
The input physics is the same used in the PARSEC V1.1 version , but for the mass-loss rate which is included by considering the most recent updates in literature .
We focus on low metallicity , Z =0.001 and Z =0.004 , for which the metal poor dwarf irregular star forming galaxies , Sextans A , WLM and NCG6822 , provide simple but powerful workbenches .
The models reproduce fairly well the observed CMDs but the stellar colour distributions indicate that the predicted blue loop is not hot enough in models with canonical extent of overshooting .
In the framework of a mild extended mixing during central hydrogen burning , the only way to reconcile the discrepancy is to enhance the overshooting at the base of the convective envelope ( EO ) during the first dredge-UP .
The mixing scales required to reproduce the observed loops , EO=2 H _ { P } or EO=4 H _ { P } , are definitely larger than those derived from , e.g. , the observed location of the RGB bump in low mass stars .
This effect , if confirmed , would imply a strong dependence of the mixing scale below the formal Schwarzschild border , on the stellar mass or luminosity .
Reproducing the features of the observed CMDs with standard values of envelope overshooting would require a metallicity significantly lower than the values measured in these galaxies .
Other quantities , such as the star formation rate and the initial mass function , are only slightly sensitive to this effect .
Future investigations will consider other metallicities and different mixing schemes .