But the higher elevation (10,000 ft. equivalent) doesn't increase the oxygen consumption of the tissues. Exertion increases the extraction of oxygen in the tissues that are being used. Sickling of the cells isn't only from lower oxygen issues, it's the acidotic environment that is created in a low oxygen environment (which is a combination of low oxygen concentration AND the depletion of oxygen of the muscles and those cells switching to anaerobic metabolism and creating lactic acid)