Cyril Dessel leads a breakaway up the Col de la Bonette during Stage 16 of the 2008 Tour de France.
AP Photo/Christophe Ena
If you are a lowlander and have traveled to the mountains to bike, hike, ski, race, or sightsee, you may have experienced uncomfortable symptoms of high altitude. Perhaps you got a rip-roaring headache, nausea, or just felt lousy all over.
Still, you've heard that high-altitude training is "good" for you. But now you're wondering if it's really worthwhile.
In this column I will explain the basics about how altitude affects the body, its benefits and the downsides. In Part II, I'll look at some recommendations for utilizing altitude training for sea-level racing and for mountain racing.
The Air up There
The reality is the density of oxygen in the air decreases in direct proportion to increasing altitude. This is not due to a change in the actual percentage of oxygen, rather it is caused by the change in atmospheric pressure. More pressure at sea level forces more air into your lungs and less pressure at altitude means less air. In other words, when you take a normal breath of air at altitude, you will have less oxygen in your lungs than you would if you were to take the same size breath at sea level.
Being an aerobic animal, you know your muscles want and need plenty of oxygen for endurance sports. To compensate for less oxygen and reduced pressure, the body tries to adjust, occasionally rebelling. The most important compensations include an increase in breathing rate (causing some people to hyperventilate) and an increase in blood flow at rest and during submaximal exercise.
Additional responses to changes in altitude can include increased resting heart rate, lightheadedness, headache, insomnia, nausea and loss of appetite. As altitude increases above 15,000 feet, people may experience vomiting, intestinal disturbances, dyspnea (labored breathing), lethargy, general weakness, and an inability to make rational decisions.
In the first few days of altitude adaptation, cardiac output and submaximal heart rate may increase 50 percent above sea level values. No wonder people feel like their hearts are going to leap from their bodies!
Because your body requires the same amount of oxygen to work at altitude as it does at sea level, the increase in submaximal blood flow partially compensates for reduced oxygen levels.
In terms of total oxygen circulated in the body--at rest and during moderate levels of exercise--a 10 percent increase in cardiac output can offset a 10 percent reduction in arterial oxygen saturation. In other words, your heart can pump 10 percent faster to compensate for 10 percent less oxygen in your bloodstream.
It is beyond the 10 percent range where things get tough. The greatest effects of altitude on aerobic metabolism seem to be during maximal exercise.
At top intensities, the ventilatory and circulatory adjustments to altitude cannot compensate for the lower oxygen content of arterial blood. This means the athlete has to slow down to reduce the demand for oxygen.
Adaptations to Altitude Stress
With all the seemingly negative effects, why would someone want to train at altitude? The biggest reason to train at altitude is the body's long-term adaptation, which is an increase in the blood's oxygen-carrying capacity.
This is partially due to an altitude-induced increase in erythropoietin (EPO), the key chemical that stimulates increased red blood cell production. Altitude exposure also causes an increase in 2.3 DPG, the chemical that makes oxygen more available to the muscles.
During the first few days at altitude, there's a decrease in plasma volume. Because of this decrease, red blood cells become more concentrated. For example, after about a week at 7,400 feet, the plasma volume is decreased by 8 percent, while the concentrations of red blood cells and hemoglobin are increased by 4 and 10 percent, respectively.