High elevations, where oxygen is scarce, can be really tough on the body, especially for today’s time-crunched adventurers who rarely have space in their busy schedules for long adaptation periods. At altitude, you dehydrate more easily, your body has to work harder just to survive and, depending on how high you go, you can be at risk for various degrees of altitude sickness. But sometimes outdoor adventures and competitions call us into the mountains, by bike or by foot, where we must perform at our very best. So how do we handle it?

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All of this occurred to me last week when I arrived in Leadville, Colorado — at 10,152 feet, the highest incorporated city in America — for the Leadville Trail 100 MTB (or “Race Across the Sky”). Just walking around town after the pre-race check-in, my lowlander body shifted into a higher gear to pull oxygen from the rarefied Rocky Mountain air. My resting heart rate leapt by nearly 30 percent, and the smallest actions, like lifting a beer can to lips, caused me to suck wind. This was alarming, with a major race looming, but it wasn’t unexpected.

CARMICHAEL’S TIPS, IN BRIEF

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1. Hydration: your body will dry up faster than normal.
2. Arrive Early or Late: arrive 18 hours of competition or seven to ten days out.
3. Know Your Limits: ride conservatively, and use a power meter.
4. Prep: show up at the starting line in the best shape possible.

As you go higher in elevation, the air becomes less dense with oxygen molecules. When you take a lung-filling breath, there are fewer oxygen molecules in the air than there would be at, say, sea level. In response, your heart rate increases to send a higher volume of relatively oxygen-poor blood to the muscles. Most people won’t notice any noteworthy performance difference at elevations up to 5,000 feet above sea level. From 5,000 to 8,000 feet, an athlete should feel perfectly normal at rest, but will likely be more easily winded while exercising. But above 8,000 feet, all bets are off.

I asked legendary cycling coach Chris Carmichael about what happens to the body at altitude in practical terms. Carmichael founded Carmichael Training Systems (CTS), which has trained thousands of athletes for high-altitude events like the Leadville Trail 100 MTB (for which they trained 59 athletes this year). He teaches how to stack the odds in your favor the next time you head for the hills — er, mountains.

According to Carmichael, people who normally live at sea level “get out of breath just walking up a flight of stairs” above 8,000 feet. And as far as biking through the mountains: “You reach your maximum sustainable intensity level much more quickly”, he said, adding that some people “see a 10 percent drop in sustainable power at lactate threshold starting around 5,000 feet.” So a fit cyclist who can maintain 250 watts (lactate threshold) at sea level is likely to reach lactate threshold at 225 watts in the thin air of 8,000 feet (and possibly as low as 5,000 feet). From there, maximum sustainable power output declines steadily as elevation increases. Near the summit of Columbine Mine, that max sustainable power output is only 70 to 80 percent of normal.

So what can you do to improve your high-altitude performance, outside of buying a second home in Leadville or sleeping in an altitude tent? Here are Carmichael’s tips:

Stay Hydrated

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Worse than all of the performance drawbacks just discussed is dehydration. The air up high is dry, which means sweat dries quickly and our bodies use a lot of fluid just humidifying the air we draw into our lungs. As a result, we dry up quickly, damaging our power output and performance far more quickly than hypoxia. Staying hydrated is stupid simple; just reach for your water bottle often.

Arrive Early or Late

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Practically speaking, showing up the afternoon or evening before an event is probably best. “The best times for sea-level athletes to arrive”, said Carmichael, “are either within 18 hours of competition or seven to ten days out from competition.” It’s not enough time to properly acclimate, but it’s enough time for your body to adjust respiratory habits, reduces the immediate stress of travel and gives you time to focus on the event itself. The worst time to arrive, according to Carmichael, is two to four days before your event: “You’re more likely to be feeling the impact of disturbed sleep, fatigue from travel, and dehydration.”

Know Your Limits

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“All riders have to understand where their limits are, and be careful about when and how often they exceed those limits”, Carmichael warned. So if you’re a cyclist, bite the bullet and get a power meter. Time-crunched athletes racing at high elevations need to ride conservatively enough to toe the lactate threshold without crossing it and burying themselves with too big an effort. Power meters are crucial to helping riders gauge their efforts. Also, if you have room in your calendar and the means to make it happen, a short altitude training camp of two to five days a month before competition can help you learn how your body responds to altitude before the big day.

Work Your Ass Off

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Above all else, Carmichael said that the most important thing is to show up at the starting line or trailhead in the best shape possible. “The altitude will take your power output and pace down a notch”, he said, “but it’s your choice where that starting point will be.”