This seems like a strange post from someone living in Lincoln, NE. There are several reasons why it's been on my mind, however. I was in Keystone, CO recently for a meeting and went for several training runs. My heart was practically pounding out of my chest. My recent post about the Wyoming Marathon also reminded me of the joys of running at altitude. Finally, my next marathon will be another one at altitude. Have to check Colorado off the list!
Altitude probably doesn't affect endurance performance until you reach almost 5000 ft. After that, however, your VO2 max (maximum ability to transport and use oxygen) declines about 3% for every 1000 ft of elevation. There are several basic physiologic principles that explain why. At altitude, the partial pressure of oxygen declines. In order for your heart to pump enough oxygen to all of your tissues, your heart rate speeds up. In order to get more oxygen into your lungs, your breathing accelerates. You lose water in the form of water vapor from increased respiration. The above changes affect the pH balance of your blood. In order to try to maintain normal pH balance, your kidneys diurese. This leads to further dehydration.
The physiologic effects of altitude begin almost immediately. Your body responds by making more red blood cells to carry oxygen, but this process takes time. Full acclimatization takes weeks. Ideally, one would arrive several weeks before an event at altitude. For most of us, that's not an option. Acutely, the best thing to do is drink a lot of water to negate the effects of dehydration, adjust your expectations, and enjoy the views and cool mountain air, however thin it may be.
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