A thousand feet a day. Another traditional mountain-climbing maxim. Hence mountains in the 15,000- to 19,000-foot range would take about a week; 20,000- to 25,000-foot peaks, three weeks; 8,000-meter peaks (higher than about 26,250 feet), six weeks—not because of the technical difficulty of the climbing or the number of feet to be ascended, but simply because the average human body requires that much time to adjust to the lack of oxygen at high altitude.
Enter the new paradigm: speed. If the Eiger could be done in eight days, why not seven, or three, or one? The record for climbing the North Face of the Eiger is now less than seven hours. That's fine for summits under 16,000 feet. But on the high peaks, genetics has gotten in the way of modern man's ever-accelerating pursuit of acceleration. Humans evolved at or near sea level, where the air is 78 percent nitrogen, 21 percent oxygen, and 1 percent trace gases, such as carbon dioxide. Along with food and water, oxygen is necessary to keep our body's 100 trillion cells alive. Like a sophisticated, finely tuned engine, the human body is calibrated to perform optimally with air that contains 21 percent oxygen at 14.7 pounds of atmospheric pressure per square inch at sea level. Drive the average human machine up 10,000 or 20,000 feet and it will start sputtering and choking like a car with a maladjusted carburetor. Although the relative percentage of oxygen in the air remains constant, the higher you go, the more the air pressure drops—and the more the pressure of oxygen drops in turn. Imagine a column of air five or six miles high. At the bottom of the column—sea level—the weight of all the air above compresses the air below. Halfway up the column, at around 18,000 feet, there's half of the pressure and thus half of the oxygen. Near the top of the column—say, on the summit of Everest (29,035 feet)—there's only one-third the pressure that exists at sea level and thus only one-third the oxygen.
No way around it. We were not designed for high altitude, and by God, you know it every time you go up there. That said, for years mountain climbers have been attempting to preacclimatize—hiking, climbing, skiing, or just hanging out at elevations lower than their goal but higher than their home. Doing a few fourteeners before heading for Mount Foraker, scrambling in the Alps before climbing in the Andes. Still, although these preclimb climbing trips have honed many an alpinist's mental acuity, mountain acumen, and technical skill, they are usually too short to effectively jump-start physiological acclimatization. The only way to acclimatize for high-altitude mountaineering has been the slow way: Go up high and stay there until you stop puking.