Exceptional endurance

Eero Mäntyranta (1937-2013), a Finnish Olympian, had naturally high hemoglobin levels in his blood, surpassing the average adult male range of 13 to 17 grams per deciliter. His levels were consistently over 20, even exceeding 23 while in his 70s.

Hemoglobin's role is to carry oxygen to the muscles. Higher hemoglobin levels mean more oxygen delivery and, consequently, increased muscle endurance. 

Throughout his career as a cross-country skier, Mäntyranta was often accused of using performance-enhancing drugs to boost his hemoglobin. However, a 1993 medical study, years after his Olympic achievements, revealed that his high hemoglobin was due to genetics, not drug use. He had Primary Familial and Congenital Polycythemia (PFCP), a genetic condition that causes an increase in red blood cells and hemoglobin due to a mutation in the erythropoietin receptor (EPOR) gene.