This article, written in Spanish by Alvero et al., is based in a study on the lactic acid levels done in 33 marathon runners of different performances at the end of the race.

The abstract of this article is available at https://www.laktate.com/informacion/lactato-en-el-deporte/concentraciones-de-lactato-tras-una-maraton-en-relacion-con-los-anos-de-entrenamiento-y-la-mejor-marca/, where you will also find a link to access the original article, written in English.