If you have plans to travel to the Sierras or the Rockies or many of high altitude competition venues in the United States, you'll need to know a little about how your body will respond to high altitude.
Those of you going to high country to compete or train can find the experience to be more rewarding if you understand the altitude environment and take intelligent protective measures to ensure optimal performance. Along with the clean air and sunshine come other conditions: less oxygen pressure, usually low humidity, and intense solar radiation.
As an individual progresses from sea level to higher and higher altitudes, the percentage of oxygen in the air remains constant, but the amount of atmospheric pressure forcing the oxygen into the lungs is less. Consequently, this reduced pressure of air at altitude makes breathing more difficult. Your body compensates for the thinner air by increasing respiration and heart rate to maintain an adequate flow of oxygenated blood to the tissues.
As an individual stays at altitude, there are several physiological changes that take place over time. This is called acclimatization. First, there is an increase in hemoglobin, the substance in the blood responsible for carrying oxygen. The body also begins to produce more red blood cells, and this enables the blood to carry more oxygen as well. The net effect of this acclimatization to high altitudes is a gradual improvement in the performance as you go harder or higher on your trail rides or races.
Although a diminished oxygen supply to the blood is the most obvious environmental factor at high altitude, dehydration from low humidity is also a factor to consider. Since water is the basis for your body's oxygen transport system (blood plasma portion) loss of plasma through sweating dramatically magnifies the effects of ability of the blood to transport oxygen to the working muscles.
A loss of two to three percent of normal body water (a few pounds) creates a perceptible loss in performance ability. Dehydration is, thus, a source of the symptoms associated with altitude discomfort - headache, slight dizziness, mild nausea, difficulty sleeping, all of which usually happen in the first three days.
Water, energy drinks and juices should be the drinks of choice in rehydration. Try to use coffee and alcohol in moderation since they tend to dehydrate you more because of the effect they have on urine production (dieresis), despite their uses in momentarily decreasing your thirst or fatigue. A final note on food. A general carbohydrate diet, and a decrease in the amount of protein ingested, will also lighten the load on your body as it works to restore a comfortable physiological balance.
Exposure to sun at moderate to high altitudes can cause both acute and chronic adverse effects on the skin. This is especially true if you have very light skin, since you will be more sensitive to sunburn. Sunlight is most intense when the sun is directly overhead because the atmosphere screens fewer rays. This occurs particularly between 10:00 A M. and 2 P.M. in the summer months. If you are prone to such burning, avoid riding during this time of day, or take other precautions.
Many mountain bike cyclists may curse altitude, but it seems that more and more events are taking place at moderate altitude. By understanding the effects of altitude, you can learn to enjoy the time spent in the clean mountain air. It is all part of understanding your body and off road cycling.