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The Science of High Performance at High Altitude

“A lot of people think, ‘Oh, if I go up to altitude for a weekend and come back down, it’ll be a benefit.' But it’s the opposite."


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There’s a reason the U.S. Olympic and Paralympic Training Center was built in Colorado Springs. At 6,000 feet, high in the Rocky Mountains, the center allows America’s elite athletes to get the benefits of working out in an oxygen-depleted environment.

Hypoxic training, or training at altitude for an event to be held at a lower elevation, is a time-tested approach to sports performance enhancement. Sometimes called “the legal version of blood doping,” athletes who train at altitude can stimulate the production of oxygen-carrying red blood cells without the use of illicit substances or procedures.

Last summer, professional triathlete Mollie Geyer (who races under her maiden name, Mollie Hebda) tested this protocol when she spent about a month training in Park City, Utah. The former Marine Corps officer, who ran track for the United States Naval Academy, traveled from her San Diego home at sea level to nearly 7,000 feet elevation to prepare for the season ahead. Though she stayed longer than many people would think they need to in order to gain a benefit, she said it still wasn’t enough.

“A lot of people think, Oh, if I go up to altitude for a weekend and come back down, it’ll be a benefit. But it’s the opposite, because it takes a little while for you to even do any workouts [at altitude] that aren’t super easy.”

This is because the body needs time to acclimate to the thinner air at altitude. Though many gadgets and training hacks promise to help athletes simulate altitude, the reality is that it takes time at altitude—where there is less oxygen, because there’s less pressure to keep air molecules close together—to train and race at altitude.

“If you can only dedicate two weeks to training at altitude, you’re better off just doing hard workouts [at home], because you’re not even going to benefit from it at that point."

The altitude acclimation process can take longer than most assume.  “If you can only dedicate two weeks out to training at altitude, you’re better off just doing hard workouts [at home], because you’re not even going to benefit from it at that point,” said Geyer.

Last year, Geyer spent the first week of her altitude training doing easy workouts to start the adjustment process, and was only able to build into harder workouts in the second week—and even then, she says a month was not enough time to build into her biggest workouts.

Adjusting her nutrition was also a big part of getting used to training at altitude. Not only did she need more calories to fuel her body’s efforts to get enough oxygen to function, she discovered her gut didn’t have the oxygen required to digest food and support exercise at the same time. In the first week of training, she often experienced stomach cramping during workouts, the result of her body competing for resources; when she stopped eating breakfast before workouts, the cramps ceased.

Over time, Geyer was able to re-introduce pre-workout nutrition, but it looked much different than what she normally used at sea level. Instead of her go-to pre-workout breakfast of peanut butter on toast, she opted for what she called “fast carbs.”

“I’d have a Coke before a track workout,” she said with a laugh, explaining the lack of fat or protein worked to fuel her muscles with less gastrointestinal distress. An unconventional breakfast, to be sure, but at altitude, much is unconventional.

Photo: Charlie Crowhurst/Getty Images
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Altitude and the human body

Dr. Tracy Cushing, associate professor of emergency medicine, wilderness, and environmental medicine at the University of Colorado-Anschutz Medical Campus has researched what happens to the human body at altitude. Her interest in performance at altitude is not just professional, but personal. As a Colorado resident who competes in iron-distance triathlons, she lives and trains almost 5,500 feet of elevation.

Cushing knows firsthand the feeling of being “under pressure” when trying to exercise at higher elevations. It’s the result of being slightly out of place as humans, who naturally function optimally at lower elevations. At higher elevations, the body can go a little haywire.

When you’re in a low-oxygen environment, your body responds automatically by hyperventilating, or taking quick, shallow breaths. Though this helps bring more oxygen molecules into the lungs, it can make you feel dizzy.

“That causes you to have what’s called respiratory alkalosis,” Cushing said, a state where there is less carbon dioxide in the blood and a buildup of bicarbonates in the system. To maintain homeostasis, these bicarbonates must be excreted through the kidneys. In other words, not only will you be breathing faster at altitude, but you’ll feel the need to pee a lot.

“That happens usually about 24 to 48 hours after getting to altitude, so it’s really important to stay well-hydrated, both to prevent dehydration and because you’re going to eventually start diuresis as your kidneys start to compensate for what your lungs are doing,” Cushing said.

Depending on how high up you go, you may have additional physiological changes. “The real changes in physiology start to happen at elevation above about 6,000 feet,” Cushing said. And they only get worse the higher you go. “Above about 12,000 or 13,000 feet, it’s just difficult for human physiology to compensate for the lack of oxygen in the air,” she said. This means that not only will performance suffer, you might get sick, too.

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“The worst hangover you’ve ever had”

Altitude sickness is no joke. “Acute altitude illness is often associated with a very bad headache that’s quite often described as the worst hangover you’ve ever had,” Cushing said. Vomiting, insomnia, and shortness of breath are also common symptoms of altitude sickness.

While it’s entirely normal to feel short of breath when exercising or even just walking at altitude, experiencing breathlessness at rest could signal a problem. Swelling in the extremities or the face, loss of dexterity, and being clumsier than normal are also red flags that your body isn’t happy with the elevation.

At very high altitudes or in severe cases, altitude sickness (also known as acute mountain sickness) can lead to high altitude pulmonary edema, which is a build-up of fluid in the lungs. High altitude cerebral edema can also arise. This is the most severe form of altitude sickness, where fluid builds up in the brain. Both of these forms of edema are life-threatening, and immediate medical treatment, which typically includes oxygen therapy, is paramount.

Most athletes, especially endurance athletes, assume that because they have a certain degree of fitness they’re exempt from altitude sickness. But Cushing says that isn’t the case: “It doesn’t matter how fit you are when all of your fitness is acquired with fully-oxygenated air. You’ll still feel it when you ascend to high elevations too quickly. Human physiology can only be pushed so far, so quickly.”

This is why acclimation is such an important part of training and racing at altitude. It’s not realistic to pop over to a high-elevation destination for a weekend and expect to be able to perform well. The body needs to adjust, and that takes time. Over weeks and months the body does adjust by creating more red blood cells, which help bring oxygen more efficiently to the cells that need it.

"Human physiology can only be pushed so far, so quickly.”

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Can you mimic altitude at sea level?

Though some athletes flock to high-altitude meccas like Flagstaff, Arizona or Boulder, Colorado, the reality is that it’s not possible for every athlete to live and train in a mountain town. So what are the options for those stuck at sea level?

A variety of products and protocols exist with the promise of altitude acclimation for the sea-level athlete. Perhaps the most widely-known of these is to limit the amount of oxygen available to you while you’re working out. For instance, this can be achieved with a hyperbaric chamber, a room where the pressure is altered to simulate a given altitude. But at hundreds of thousands of dollars, such setups are out of reach for the average age-group athlete.

There are also plenty of cheaper consumer products that claim to help athletes get better at coping with altitude. But whether they actually work is open to debate. The same is true of at-home consumer products that claim to mimic the thin air of altitude while sleeping, promising all the benefits of altitude training without actually training in altitude. These, too, are costly (usually starting at $8,000) and probably don’t offer much benefit in terms of athletic performance, because your muscles aren’t stressed while sleeping—a critical piece of the acclimation puzzle. “[A sleep chamber] might help you not get altitude sick,” Cushing said, “but it probably won’t help you perform better on the course.”

Another device that claims to help athletes prep for how it feels to swim in an oxygen-limited state is a so-called “cardio cap,” a small accessory that’s placed on the business end of your front-mounted swimming snorkel. The cap reduces the size of the opening, thereby letting in less air with each breath. Theoretically, this is supposed to mimic the effects of high altitude; swimming equipment manufacturer FINIS reports that the snorkel cardio cap “replicates higher altitude workouts” and notes that it “increases lung workout load by 40%.” How they arrived at that specific figure and whether that’s enough to actually make a useful change to your body’s ability to complete a swim at altitude is not entirely clear.

When it comes to gadgets, Cushing says they’re little more than marketing gimmicks. “Spend your money instead on a triathlon training camp at altitude four weeks or two weeks before your race.”

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A surprising altitude hack that might actually work: heat

If gadgets don’t work, what does? One approach that seems to have some scientific teeth is heat. A small 2016 study published in Frontiers in Physiology examined cross-acclimation between heat and hypoxia and found that heat acclimation can improve cellular tolerance and exercise performance at altitude.

The idea here, the authors noted, is that “adaptation to one environmental stressor can induce protective responses upon exposure to other stressors as long as they share common adaptive responses.” This cross-acclimation happens on the cellular level, as cells become more tolerant of heat and hypoxic stress in similar ways. To wit, as far as the body is concerned, to some degree, a stressor is a stressor is a stressor.

When under stress, the body responds by releasing proteins that defend cells from that stress-induce damage. These proteins are called heat shock proteins, but the body produces them in response to lots of stressors, not just heat. Triggering that response purposefully and over a long period of time can lead to adaptive changes in the body that may help you crush your next goal.

According to that study, training in heat for 10 days may improve performance at altitude. But it’s worth pointing out that participants in the heat acclimation group saw less improvement than those in the altitude training group. Those in the heat group saw an improvement of 2:02 on average on the 16-kilometer time trial course, vs. 3:16 on average improvement for the hypoxia group.

In other words, heat acclimation might help, but training at altitude is still the best way to prepare for a triathlon at altitude. (Are you noticing a theme here?)

RELATED: Hot Stuff: The History and Science of Heat Acclimation

Photo: Agurtxane Concellon/Getty Images
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Want to go faster at altitude? You’ve got to slow down

If you can’t spend oodles of time training at altitude before a race, one strategy Cushing recommends is to plan an extra day or two at a medium-high midpoint on the way to your ultimate destination. If your plan is to race a triathlon at an elevation of between 8,000 and 12,000 feet, spend a night or two at 5,000 feet of elevation beforehand to help your body adjust. “Going from sea level to anything about 10,000 feet in one day, you’re at risk of serious altitude sickness,” Cushing said. “That’s obviously not going to be good for training or racing.”

The idea to take your time extends to race day, too. Lorena Sims of Auburn, California, served as a water safety volunteer at several high-altitude triathlon events. During Ironman Lake Tahoe in 2013, she was stationed on a boat near the midpoint of the swim. The water was cold and the race takes place at more than 6,000 feet elevation, making for a very challenging day for many of the athletes. Cold water, which places an additional physiological stress on the body, can make the effects of altitude seem even more intense.

“I saw a number of athletes basically going from safety boat to safety boat,” Sims said. “They’d catch their breath, start swimming again, and be gasping by the time they made it to the next boat.”

Ninety-two athletes did not finish the swim that day, many of them because they just couldn’t catch their breath. In total, 20% of the athletes who started the race did not finish—though that was in part due to extremely cold temperatures that day. “It was difficult to watch because these were definitely people who put a lot of time and effort into training but missed one critical consideration: preparing for the effects of altitude,” Sims said, adding that a few of the athletes who stopped at her boat said they were only able to get to the Tahoe area some 36 hours prior to the start of the event.

“I think that’s the biggest mistake,” she said. “If you can get into town early and do some shake-out work ahead of time, I think a lot of them would have been so much better off.”

Her experience with working at triathlon races at altitude, coupled with the most recent science on performance at altitude, shapes the advice she gives athletes before each race. “Go slower on the swim than you want to, especially at the race start,” she said. “Don’t let the adrenaline make you get into an oxygen deficit right off the bat. Pace yourself carefully. Save some breath for the rest of the race.”

RELATED: The Basics of Triathlon Training and Racing at Altitude

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Practical advice for preparing for a triathlon at altitude

What do you do if you live low but want to race high? First, don’t panic. It’s possible to prepare. Our experts’ advice:

  • Try to get to your high-altitude destination as early as possible. The more time you can give your body to acclimate, the better.
  • If you can’t arrive at your destination early, plan at least one or two nights at a midpoint between your home elevation and your destination elevation. (In other words, if you live at sea level but plan to race at 8,000 feet, book a night at a hotel in a town at 5,000 feet.)
  • When you arrive to your altitude, do some low-intensity workouts to see how your body responds. “Just do some hikes, go for a swim, see how you feel,” Cushing said. “These workouts can be a good gauge.”
  • Remember that high-elevation locations tend to have high-elevation features. Train accordingly. “You have to go out there and ride big mountains if you want to race big mountains,” Geyer said. “There are no shortcuts. You have to practice climbing in real life.”
  • In the months leading up to your race, eat iron-rich foods (red meat, spinach, almonds) to help the body create more oxygen-ferrying red blood cells.
  • Avoid alcohol and caffeine, as these substances are dehydrating. Cushing warns they also blunt the hypoxic ventilatory response, which decreases your ability to acclimate.
  • Extra fueling and hydration is vital at altitude. Your basal metabolic rate increases at altitude, meaning you’ll need to eat and drink more.
  • Be on the lookout for signs of altitude sickness, which include:
    • Headache
    • Dizziness
    • Fatigue
    • Loss of appetite
    • Vomiting
    • Shortness of breath
  • If symptoms become severe, seek emergency medical treatment. These symptoms may include:
    • Loss of coordination
    • Tight chest
    • Inability to breathe, even at rest
    • A cough that produces a white or pink froth
  • Adjust your expectations. The splits you are able to hit at sea level will be vastly different from what you can do at altitude. Develop a race plan that uses Rate of Perceived Exertion (RPE) instead of time splits, which will allow you to take a more realistic approach to race day.

RELATED: How to Fuel When Training and Racing at Altitude