Merckx index said:
There surely must be an auto-EPO syndrome out there, in which your HT goes up to 60 because of weird metabolism. Actually, there are genes known to do that in mice.
Some Scandinavians have a distinct genetic advantage over everyone else. See the following vintage paper;
Truncated erythropoietin receptor causes dominantly inherited benign human erythrocytosis
(translation: some people carry a mutant EPO gene that results in naturally high hematocrit levels)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC46538/pdf/pnas01462-0175.pdf
From the text:
"The clinical condition is so mild that many affected individuals are not themselves aware of any abnormality, nor do they have any sense of illness. The clinical and laboratory findings based on the study of 25 affected and 72 unaffected family members can be summarized as follows (15). Hb is remarkably high: mean male value, 204 g/liter; range, 183-231 g/liter (normal: mean, 154; range, 136-174); mean female value, 191 g/liter; range, 177-200 g/liter (normal: mean, 138; range, 124-153)."
"The proband, a 53-year-old male, whose Hb level has been 200 g/liter or greater since childhood (last
measurement, 236 g/liter), has been one of the best cross country skiers in the world, having won three Olympic gold medals and two world championships."
The skier in question is Eero Antero Mäntyranta.
50% hematocrit level is approximately 165 g/liter Hb.