Last week, I got the chance to do some runs at sea level for the first time without being injured in over a year. It’s interesting to see just how much of an effect altitude has on running abilities. Just by moving to a different altitude, I was able to go around 30 s / mi faster than in Colorado without even trying too hard. I could also run longer distances without feeling tired.
This is supposed to be why so many professional athletes train at high altitudes. If they are trained to do well at high altitude, they will do even better at sea level.