Why Altitude Affect Performance

Anyone who has moved from sea level to a high altitude and tries to run will immediately notice that their breathing is much heavier than it was at sea level. It is not that there is less oxygen in the air since at any level there is till 21% oxygen. But as the elevation increases the partial pressure declines. This affects the transfer of oxygen from the tiny air sacs in the lungs to the the blood. The result is less oxygen being driven from the lungs into the blood.

How much does the pressure change? At sea level oxygen has a partial pressure of 159 mmHg. In Mexico City it is about 125 mmHg. At the top of Mt. Everest, it drops to 48 mmHg, which is about equal to the blood surrounding the lungs. So anyone at this high altitude would find their oxygen exchange to be greatly diminished.

Human Body Response to Altitude

Review the article on VO2 Max where we discuss the ability to supply and utilize oxygen is limiting to cycling performance. This can be improved by training. Some effects are noted as the altitude increase to 2,000 feet but up to about 5,000 feet, altitude most cyclists notice little effect on the body.

Acclimating to Altitude

It takes about two weeks for the body to adapt to a change of altitude up to 7,500 feet. Every 2,000 feet requires an additional week of acclimatization. However no matter the time spent, a person will never feel like they are at sea level. See Acclimatization to Altitude


Cycling Events at Altitude

If the cycling event is mostly flat, the thinner air may more than compensate for the biological effects of the reduced partial pressure of oxygen. I have notice that when going to 5,000 feet I can ride faster. However when climbing is involved, the air reisitence is less of a factor and I start to feel the affects of altitude.

If you live at sea level and need to compete at high altutude you have a few approaches. One way is to compete within 24 hours of arrival. You will not have much in terms of acclimation but most of the symptoms of altutude sickness will not have time to show up.

Another approach is to train at a higher altude for at least 2 weks prior to competition. Alghough it may take 4 to 6 weeks to become acclimized, you get much of the benefits in the first 2 weeks.

A third approach is to devote even more time to training at sea level so as to increase your VO2 Max, so as to help offset the effects of the higher altutude.


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