IN May, soccer's international governing body, FIFA, banned international matches in stadiums at elevations higher than 2,500 meters, or roughly 8,200 feet. The concern: "Thin" mountain air can take a heavy toll on people accustomed to breathing at sea level.
Mountain sickness, also called altitude sickness, has been in the written record since at least the 16th century, when Spanish missionary Jose de Acosta described it. Traveling from the east coast of South America to the west-coast city of Lima, Peru, in the 1500s, Acosta traversed mountain passes as high as 14,000 feet. He and his traveling companions -- and their pack animals -- were unprepared for what hit them at such heights: extreme shortness of breath, nausea, vomiting, confusion and debilitating fatigue.
Some of Acosta's fellow travelers were said to have felt so ill they begged the priest to take their confessions, thinking they were on the brink of death.
After watching the pattern repeat at each high pass, Acosta concluded that mountain air was too "delicate" and "not proportionate to the human respiratory system."
Though not a scientist, Acosta was nearly right. But his findings were followed by centuries of misunderstanding.
His fellow missionaries concluded that mountain air diminished the mental capacity of the Andean natives. They also believed that fatigue occurred at high altitude because the decreased pressure meant muscles had to work harder to keep skeletons from collapsing. (This was based on the belief that a certain amount of air pressure was necessary to keep bones in place.)
It was 300 years before scientists offered a more sophisticated explanation for altitude-induced symptoms. Working at the Sorbonne in Paris, French physician Paul Bert placed animals in chambers and manipulated the air inside. Low pressure, he concluded, wasn't the direct cause of altitude sickness. The real culprit was oxygen deprivation. Mountain air has the same fraction of oxygen as sea-level air, but the air pressure of that oxygen is lower, which means fewer molecules make it into the lungs on each breath.
In the decades that followed, researchers in Europe and the Americas began to more carefully document the human body's response to altitude, many of them accompanying trekkers on mountain hikes.
