a few years ago, i took a trip to ecuador and had all kinds of crazy elevation experiences. when i got there (8500 ft to start), i was winded walking up the stairs to my hotel room. after a few days, i took a jeep into the mountains and hiked for a few days between 12,000 and 15,000 feet, which kicked my ass. then, i took buses from a village at 15,000 feet to a town by the ocean (a miserable, all-day affair). the next day i started running along the beach and must have sprinted for 5 minutes straight without even feeling winded. it was crazy, but the effect wore off after a few days at sea level, and i was back to my normal, out-of-shape self. this has nothing to do with climbing, though... so sorry for that.