Robin, Norfolk asked:
Where is the best place on Earth to run a marathon? Would gravity make a difference?
Chris - If you're running a marathon, you're presumably in a race with lots of other people and so therefore, it is, relatively speaking, a level of playing field for everybody. The difference, I would argue though, would be the altitude. If you were to go up a mountain and run, if you live up a mountain and you train regularly at altitude, then your body undergoes all kinds of adaptations in order to make you tolerate that high altitude much better; for example, you make more haemoglobin, the red stuff in your blood that carries oxygen around the body. You also have muscles that are much better able to tolerate lower oxygen tension and they make other chemicals, including one called 2,3 bisphosphoglycerate. (I know this because I've been teaching medical students at the university just recently!) This goes inside red blood cells and makes them give up oxygen from their haemoglobin more readily. So, if you went in a marathon with some people from Kenya who all live and train at high altitude, which is why they always do very well in marathons all over the world, you would be competing as someone who doesn’t live at that altitude; you also don't have the same genetic ancestry that makes that beneficial for you, and therefore, you would be at a disadvantage compared with someone who does.