IT is 4:01 a.m. The red glow of the digital clock is clearly visible through the clear plastic walls surrounding my bed. It is mid-March, and the Boston Marathon is more than a month away. If everything works as planned, I will finish it in less than three hours.
For several nights now, I've been sleeping in a giant plastic bubble as part of an unscientific but increasingly common experiment on athletic performance. The air in the tent contains less oxygen than the air in the rest of Los Angeles. By using the tent for the next few weeks, I hope to improve my body's ability to supply oxygen to my running muscles -- and shorten my marathon time.
Other hard-core runners, cyclists and cross-country skiers -- especially aging ones -- understand this desperate attempt to get faster. As bodies age, they need more training to achieve the same times, and at 36, I've already started to slow down -- at least 1 1/2 minutes over a 6.2-mile race compared with my college days.
Short of using performance-enhancing drugs, I'm willing to try almost anything for an advantage.
I'd move to the mountains if I could. Above 7,000 feet, where significantly less oxygen is available than at sea level, the body increases its production of oxygen-toting red blood cells within a few weeks.
In races at sea level, athletes with extra red cells can supply their muscles more efficiently with oxygen than their competitors from the lowlands.
The promise of such a boost draws top endurance athletes to live in oxygen-thin places, such as Boulder, Colo., or Mammoth, Calif. But for the rest of us, trapped in desk jobs at sea level, a tent filled with oxygen-thin air is a tempting alternative.
In theory, spending a large portion of each day in a low-oxygen environment can trick the body into producing extra red cells.
Research even suggests this might be more effective than simply living and training in the mountains. "Live high, train low" goes the current mantra on altitude for athletes. Living high builds up the red cell count. Training at lower elevations allows the body to exploit those cells by pushing your body as hard as possible; it is simply not possible to run as fast at high altitude.
Inside the tent, I cannot get back to sleep. And because I'm not yet acclimated, it feels hard to breathe.
I think of a John Travolta TV movie from 1976, "The Boy in the Plastic Bubble," in which he plays a kid with an immune system disorder who stays alive by living in an incubator.
At least my immune system is fine.
Over the last decade or so, tents and other types of altitude chambers have become standard equipment for many elite runners, cyclists and cross-country skiers.
Lance Armstrong was one of the early believers. Now it is hard to find a Tour de France rider not sleeping "at altitude."
Using the same technology that pumps oxygen-poor air into the tents, Nike has turned an entire house into a high-altitude dormitory for its running stars in Portland, Ore.
Horse trainers have even started boarding thoroughbreds in stalls filled with oxygen-thin air.
The technology has become so popular that last year the World Anti-Doping Agency, which sets the rules on performance aids for international competition, considered adding altitude tents to its list of "banned methods."
In theory, the tents have the same effect as injecting EPO, an artificial version of the hormone erythropoietin, which stimulates red blood cell production in people suffering from anemia. It has long been banned in sports.
The case against tents came down to the question of whether they "violated the spirit of sport." Ultimately, the answer was no, tents were simply another training aid.
Not only the elites are using them.
Amateurs account for about half of the several thousand people who have bought altitude tents, according to the two companies that control the U.S. market, Colorado Altitude Training in Boulder, and Hypoxico Inc. in New York.
The most affordable way to try a tent is renting, for about $600 a month. Buying a tent requires more commitment: A basic model sells for $6,000.
Converting a bedroom into an altitude chamber runs more than $20,000.
Since I was already training hard, it seemed unlikely that sleeping at simulated altitude could help much. But Hypoxico agreed to lend me a tent for five weeks before the Boston Marathon.
The marathon would be the main test.
Of course, many things can go wrong in a long race -- hot weather or just an off day -- so I decided to gauge the tent's effects another way.
Before I started using it, I did a "lactate threshold test," which involves running on a treadmill at ever-increasing speeds while a technician periodically pricks your finger for a blood sample. The test measures the body's ability to process lactic acid -- which accumulates in the body as muscles tire -- and is considered an excellent measure of aerobic fitness.
I would redo the test around marathon time.