China has a serious problem in Tibet with altitude sickness among its troops. This illness occurs when people who grew up near sea level (most of the world's population) move to altitudes greater than 2,100 meters (7,000 feet). Below that, the air contains 21 percent oxygen. Above that, the percentage of oxygen declines, and that produces shortness of breath, disorientation, nosebleeds, nausea, dehydration, difficulty sleeping and eating, headaches and, if you stay up there long enough, chronic and long term disability. The average altitude of Tibet is 4,100 meters (14,000 feet).What hurts you the most is the lower air pressure at higher altitudes, which means your lungs transport less oxygen to your blood. Most people can adapt, sort of. Some can't. But the Tibetans have evolved to deal with it.The majority of Chinese soldiers coming to the Tibetan highlands (which is most of Tibet) require a few days, or weeks, to acclimate. But they are still susceptible to altitude sickness if they exert themselves, especially for extended periods.This makes the troops much less effective.
Researchers recently discovered that most Tibetans evolved in the last 3-6,000 years to deal with this problem. It appears that the most of the people moving to, and staying in, highland Tibet, where those with the rare genes that made them resistant to altitude sickness. These people became the dominant population in Tibet, mainly because they were healthier at high altitudes. Nearly all Tibetans have this gene (which controls how their red blood cells operate, to maintain sufficient oxygen levels). Very few lowland Chinese have these genes.
The Chinese military is spending a lot of time, effort and money trying to solve this problem. Currently, most of the troops in the Chinese Chengdu Military Region are in the eastern, lowland half. In the western portion (Tibet), they station the 52nd and 53d Mountain Brigades, and struggle to keep these 5,000 troops fit for duty. If there's an emergency, as there was two years ago, the nearby 13th and 14th Group Armies can send troops from their lowland bases. Over 20 percent of these troops will be hampered by altitude sickness once they reach the highlands, and commanders are trained to deal with that.
Chinese troops operating at the highest altitudes (4,500 meters, on the Indian border) now have access to exercise rooms (one of 1,000 square meters and another of 3,000 square meters) that are supplied with an oxygen enriched atmosphere. Troops exercising in these rooms increase the oxygen in the blood, and are much less likely to get hit with a case of altitude sickness. Thus the troops can stay in shape without getting sick. For border patrols at high altitudes, troops usually carry oxygen bottles and breathing masks.
So far, the Chinese have only been able to limit the attrition from altitude sickness, not eliminate it.