All three men, like the vast majority of the world’s best distance runners these days, were born, grew up, and train in the East African highlands along the Great Rift Valley, at elevations of at least 6,000 feet above sea level. The thin, oxygen-poor air at these heights makes running harder and triggers adaptations like an increase in the number of red blood cells available to shuttle oxygen from the lungs to working muscles. In fact, anyone born into this environment carries oxygen-sparing traits like enhanced lung volume with them for the rest of their lives.
