A number of athletics and cycling world records have been set at high-altitude venues, for example during the 1968 Olympic games in Mexico City. Presumably the air is thinner so there is less resistance, enabling them to run or cycle faster. But surely oxygen uptake at altitude is more difficult, so there must be a point at which altitude no longer favours athletes. What is this point and why? And which tracks or velodromes come nearest to it?
Carlos Loeb, Madrid, Spain