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I am married, and while I can't say what other people are doing in bed late at night with their wives, I feel fairly certain that for a few weeks over this past winter we were the only couple on our block who were sleeping in a tent at high altitudes. Our block is not in Switzerland; it's in New York City, and our apartment has a harbor view. And yet at one point we were up around 10,000 feet. No, it wasn't a role-playing thing that involved lederhosen. It was a physical fitness thing, a training thing—a thing that theoretically made me stronger, or more fit. Which it did, or seemed to, except for the time when I accidentally got us up a little too high in altitude, an event that felt a bit like being on an amusement park ride gone amok.

Don't worry; we were fine in the end. I had asked my doctor beforehand if it would be wise for us—a guy in his forties and his slightly less aged wife—to sleep for a couple of weeks in a tent attached to a machine whose sole purpose is to deprive you of oxygen. The question caused my doctor to look at me funny for a long time and then take my blood pressure all over again. But sleeping in an altitude tent is not as uncommon as you might think. This is thanks, first, to the trend in America that sees more and more nonprofessional athletes acting, and thus shopping, as if they were professional athletes and, second, to companies that build these contraptions. Colorado Altitude Training, or CAT (altitudetraining.com), for instance, is a Boulder-based company that will, if you are so inclined, set you up in an atmospheric equivalent of, yes, Colorado, or some other high-up place.

"But what's the point of this?" my doctor persisted, as did my wife, especially on the first night that we were getting ready to sleep in a plastic tent filled with high-altitude-esque air. It's all about your lungs, in addition to your wife's lungs, if your wife is part of your altitude-training test regimen, as my wife was, due to the fact that we are married and not currently arguing. It's about your lungs and your ability to produce red blood cells, which carry oxygen to your muscles. The more red blood cells you have, the more endurance and power, which, if you are a novice runner like myself, might translate into a faster running time, and, if you are my wife, who is a preschool teacher—a job that is physically more demanding than a lot of triathletes' regimens, much less office workers'—endurance and power way past snack time.

But how exactly does sleeping in a plastic tent with a giant filtered air blower hooked up to it cause one to make more red blood cells? Well, I don't want to get too technical, given that my brain has been living in an oxygen-deprived environment, but at high elevations, the chemical composition of the air is the same as the composition of the air at sea level. The difference is in the air pressure. In the lower air pressure on an Andes peak, your lungs draw in fewer oxygen molecules with each breath. The hypoxic air generator filters out oxygen mol-ecules from the air in your apartment; thus the air pressure stays the same, but the oxygen content is adjusted to simulate what your lungs would draw in if your lungs were working in the Himalayas—the idea being that when our lungs become used to working with fewer oxygen molecules at high altitude, then they are even more efficient at lower altitudes. You can train while you sleep, which is something we can all get behind, and when your lungs wake up you are producing more red blood cells while out running along the beach. (The tent has been so effective, in some cases, that the World Anti-Doping Agency at one time considered banning it.) The CAT people have rigged up all the bedrooms in an entire houseful of Nike-sponsored Olympic runners in Oregon, and, aside from its use by athletes, the CAT system is used by the military and by horse trainers in their thoroughbred's stables.