Extreme High Altitude, Fitness, and Acclimatization

A Practitioner’s Perspective

[Aconcagua | February 3, 2018] I am doubled over on my knees at 22,500ft above sea level. I have been moving nonstop for almost thirty hours at an ever-diminishing pace; over the course of the prior night my forward progress cratered to no more than a half mile per hour. Now, I am a mere 400 feet from the summit but it could as well be worlds away. Every step is a battle. If - and this is a big “if” - I manage to reach the top, and then return to my starting point in the valley some 13,000ft and twenty miles below where I currently am, the women’s speed record on the Aconcagua 360 route will be mine.

Altitude is hard. Why? The objective answer is hypoxia: due to changing atmospheric pressure, the environment we operate in becomes increasingly hypoxic, i.e. oxygen-deprived, as we ascend from sea level towards the rarefied air that surrounds the high peaks of the Andes, the Himalayas, or the occasional 15,000ft+ peak outside of those two major mountain ranges — Denali and Kilimanjaro are well-known examples.

Just like there has been a rise in ultra marathon participation over the last decade, there is now a lot more interest in high altitude mountaineering: from Kilimanjaro to Everest, high altitude expeditions are becoming more mainstream. High profile mountaineers are making headlines by climbing extreme high altitude peaks in less and less time – just think about Kristin Harila and Nirmal Purja with their respective 14 Peaks records, or the lesser known but equally impressive feat by Roxanne Vogel of summiting Mount Everest in less than two weeks door-to-door from her sea-level home in the US (warning: don’t try this at home; all these mountaineers had tremendous acclimatization or pre-acclimatization protocols). In the process, the ill and potentially fatal effects of high altitude are rubbing shoulders with more and more unsuspecting first-timers – and even though a lot of excellent material has been published about the science of acclimatization to high altitude, there are several stubborn misconceptions amongst recreationalists. This is not just a matter of setting newcomers to high altitude up for failure on their initial expeditions; it is a question of life and death, as inadequate acclimatization coupled with summer fever has been the cause of many fatalities.

Due to the crossover between my roles as a record-setting high altitude endurance athlete – I have set speed records on Aconcagua and around the Annapurna Circuit, among others – and an expedition leader and high altitude guide for AWExpeditions, I have a somewhat unique perspective on the topic of acclimatization. I am by no means the only practitioner with significant cross-over between big peak guiding and high altitude endurance – Karl Egloff is the preeminent contemporary example on the men’s side – nor am I the ultimate authority on high altitude, but there aren’t very many of us who both run and guide at high altitude. Most professionals choose either guiding, or a career in endurance sports; not both. That’s why I want to share my personal observations to address several of the most common misconceptions head-on.

Let’s talk about what works and what doesn’t work at high altitude from a practitioner’s perspective.

Misconceptions About Performance at High Altitude

MISCONCEPTION: Acclimatization happens over the span of a few days

It is true that even brief exposures to high altitude trigger the process of acclimatization – but the fact that your body is beginning to display adaptations to the hypoxic environment does not mean that you are acclimatized. Acclimatization is a long-term process. Scientists have determined that complete acclimatization to altitude as measured by full hematological adaptation, when the hypoxia-catalyzed increase of red blood cells reaches a plateau and stops, is measured in weeks and months rather than days. A 2007 high altitude study by GR Zubieta-Calleja found that full hematological adaptation took a little over a week and a half (11.4 days) for every 1000 meters or 3,300ft of altitude gained. That means that, to completely acclimatize to 5,850m – the elevation of Aconcagua’s typical high camp from which most climbers start their summit bid – you would need to spend more than nine weeks (!) at said altitude.

Those of us who spend a lot of time at very high and extreme altitude – which, scientifically, is defined as the elevations between 11,500-18,000ft, and then 18,000ft and above – know well that most typical expedition schedules are laid out in such a way to allow upward progress at the very bottom edge of a defensible acclimatization schedule. After all, most climbers and adventurers have jobs and families waiting for them at home; they don’t have all the time in the world to spend in the mountains.

The problem is that, for newcomers to the high altitude world, the idea of spending an extra day or two at an approach camp to acclimatize often seems generous. In truth, that extra day or two of acclimatization at an approach camp is typically the bare minimum that may allow the average expedition team member to progress to higher altitudes without serious illness. Think back to the numbers around full hematological adaptation: even to “just” fully acclimatize to the 14,000ft level – roughly the elevation of Aconcagua’s basecamp – you would need to spend 45 days or six and a half weeks at basecamp. Those time periods, of course, are unrealistic for anyone but mountain professionals and seasonal staff at those encampments. Which, by the way, is why so many speed records on Aconcagua are set by local guides or porters towards the end of their 3-4 month season on the mountain.

Side note: Commercial outfitters know fully well that the shorter an itinerary, the more affordable the expedition becomes both from a time and money perspective, the better it will sell. Thus most commercial high altitude expeditions are likely to follow the shortest possible timeline that can support a successful summit for most climbers. This means that, if you are planning an independent expedition, any commercial itinerary should be a guideline for your absolute minimum number of days at altitude. Climbing independently does NOT mean being able to move up a mountain faster than a commercial expedition; on the contrary, if you plan your expedition well, my recommendation would be to ADD days to any commercial schedule that you may be able to find on the internet.

WATCH OUT. Ground operators that are based at high elevations don’t always account for the acclimatization boost that their guides and staff enjoy from living at those high altitudes. Examples are Peru and Bolivia where outfitters may be headquartered in major urban centers that are located at 10,000-14,000ft above sea level. You’ll find off-the-rack itineraries from local outfitters to climb mountains like Bolivia’s 19,974ft Huayna Potosi in the span of just three days - which is at the bare edge of what is realistic for those who are thoroughly pre-acclimatized to 12,000ft and frequently venture to higher altitudes (i.e., local guides or folks who have spent weeks in the region), yet completely unsafe for those international visitors who are traveling from sea level specifically to join an expedition.  

MISCONCEPTION: The fitter you are, the faster you can ascend a high altitude mountain

It is common knowledge that training is essential for success on a big peak. You need leg and core strength to sustain progress through steep terrain; upper body strength, to muscle your heavy pack and all the gear it takes to safely ascend an expedition peak. And you need superior cardiovascular fitness to sustain long hours of physical strain without any real chance for quality rest and recovery in between your daily efforts.

While all of that is true, how well-trained you are unfortunately has almost nothing to do with how effectively your body acclimatizes. Studies have found that incidence of acute mountain sickness has little to no correlation with factors such as physical health and fitness. On the contrary, the key predictors of your body’s ability to acclimatize are your rate of ascent (the slower the better), prior performance at high altitude, and genetics.

The takeaway is simple: having crushed your pre-expedition training, or being an elite athlete at low elevations, does NOT set you up to acclimatize more rapidly than your less-fit teammate – not even a little bit.

“Important to the Care of Athletes Is That a High Level of Aerobic Fitness Is Not Protective Against Development [of Acute Mountain Sickness].” American College of Cardiology - Exercise and Elevation

So why train at all then? Superior strength and fitness are important to success at high altitude, but in a less obvious way than you might think. Recovery and self care are the secret to sustaining high performance throughout a multi-day, multi-week, or potentially even multi- month effort. The stronger and fitter you are, the easier it will be for you to recover from the daily hard efforts that are normal at high altitude. Your pre-expedition training provides the foundation for you stay at high altitude for more days with fewer adverse effects. In addition to better recovery, your extra stores of strength and cardiovascular fitness will also make it easier for you to excel at self care in a challenging environment. Note that this is NOT the same as allowing you to ascend to ever higher altitudes at a faster rate. Do not fall victim to this fallacy!

Most newcomers to altitude don’t grasp that there are two different timelines: the intraday timeline of covering a certain distance and elevation gain, and the multi-day expedition schedule. While the intraday timeline is variable with your fitness, the multi-day expedition schedule is not. The fitter you are, the fewer hours you will need to spend on any given segment (say, hiking from Camp 1 to Camp 2) while still being able to keep your heart rate low – an important factor in avoiding acute mountain sickness. However, you still have to spend the same number of days and nights acclimatizing to a given altitude.

Here’s the mechanism of how superior cardiovascular fitness should benefit your progress at high altitude:

A well-trained athlete will be able to keep her heart lower and cover a hypothetical two mile hike with 2,000 feet of vertical gain faster than a casual hiker with inferior cardiovascular fitness. If managed properly, that means two things within the context of a high altitude adventure: the athlete has more time to rest before and after the hike, and she is less susceptible to acute mountain sickness precisely because she is able to keep her heart rate low. Because the athlete has the same acclimatization requirements as the casual hiker, upon completing the two mile / 2,000ft vertical gain segment at a (to her) leisurely pace she settles in to hydrate, eat, rest, and set herself up for a good night’s rest at the new altitude. She wakes up the next morning better recovered and with fewer symptoms of acute mountain sickness than the casual hiker, who had to spend more time at a higher heart rate to reach the same elevation as the athlete.

What unfortunately happens much more commonly in the field is this:

The well-trained athlete considers the same 2 mile hike with 2,000 feet of vertical gain a test of his physical ability. He charges hard, pushing his heart rate as high as the hypoxic environment will allow – after all, that’s what he got used to while training – and races through the 2 mile / 2,000ft segment. That in and of itself is bad enough, and a recipe for acute mountain sickness a few hours later. (Read: Exercise exacerbates acute mountain sickness at simulated high altitude.) Also not uncommon: instead of sticking to our ¨hypothetical 2 mile & 2,000 feet of vertical gain segment, our well-trained athlete decides to cover more miles and more altitude than intended; after all, there are lots of hours left in the day. Now he isn’t just predisposing himself to acute mountain sickness due to high levels of exertion; he is also violating the multi-day acclimatization schedule that is required to allow human physiology to initiate the chemical adaptations that are needed for our bodies to perform in a hypoxic environment. As emphasized previously, that multi-day acclimatization schedule is not correlated with fitness.

In short — unless coupled with a thorough understanding of the effects of high altitude, superior fitness is frequently nothing but an enabler for athletes to get themselves into deeper trouble faster.

“High Altitude Cerebral Edema (HACE) Is a Severe and Potentially Fatal Condition Associated With High Altitude Illness That Is Often Thought of as a Late or End-Stage Acute Mountain Sickness (...); It Is Critical That It Be Rapidly Diagnosed and Managed, as It Can Progress to Coma and Death as a Result of Brain Herniation Within 24 Hours." National Institute of Health

When it comes to high altitude endeavors, your pre-expedition cardiovascular training counterintuitively lays the foundation to help you minimize relative exertion at high altitude. You train hard prior to a high altitude expedition so that you DON’T have to work hard while on the expedition. The less hard you have to work on a relative basis (as measured by effort expended / your personal hypothetical maximum effort ) on any given day during a drawn-out high altitude adventure, and the better you can recover from each of those daily efforts, the more likely you are to accomplish your eventual goal – be that a summit, a speed record, or a technical route. Your cardio fitness may enable you to have a shorter and “easier” summit day than someone who is less fit – but up until you are at the highest camp and in position for said summit day, your training is not a ticket for faster-than-average upward progress on the mountain.

STORY TIME. I remember well an evening that I spent in the Sherpa village of Gyele, enjoying the company of Everest pioneer David Breashears. Gyele is located at 13,400ft (4,000m), a relatively modest altitude for the Khumbu. David and I had each been in Nepal for a while - I had just guided a Mera Peak expedition and then set a speed record around the 136 mile Annapurna Circuit - and both of us were well acclimatized. We were enjoying the comparatively thick air and comfortable tea house lodging when a young Frenchman in running attire burst through the door of the tea house dining room. 

We got into chatting with the late arrival and quickly learned that he was a trail runner - not that the attire hadn’t given it away - new to the Himalayas, and had flown into the mountains from Kathmandu (4,500ft above sea level) that very morning. Excited about the trail, the beauty, and the challenge of it all, he had set out from the airport in Lukla midday and covered double-digit miles and 4,000 net feet of vertical gain over the course of the afternoon. The runner was in great physical shape, a bit tired but exhilarated by his adventure, and excited to have gained so much ground so quickly. David and I, on the other hand, were on high alert: thanks to years of experience we each knew without a doubt that, even though the sheer distance and vertical gain obviously were within the physical capability of the young man, his ascent profile without prior acclimatization was a recipe for dangerous consequences - HACE and HAPE can be fatal if not recognized and treated properly. We tried without success to convince the runner to descend to a lower sleeping elevation. When it became clear that he was hell-bent on staying at Gyele for the night, we did impress on the runner that he needed to make himself known in the night if he needed help.

Sure enough - at 2:30am, I was roused by a feeble knock on the door of the bunk room that had been allocated to our party. The French runner reported a racing heart, a severe headache that wasn’t improving with ibuprofen, and dizziness and nausea to the point of throwing up: classic symptoms of severe acute mountain sickness that can progress to high altitude cerebral edema if left untreated. David provided dexamethasone from his personal emergency kit which helped the runner make it through the night before descending to a safer altitude at daybreak.

MISCONCEPTION: The less time you spend up high, the better – you will get weaker while spending time high up on a mountain.

Time at altitude is a double edged sword. Time up high is absolutely essential for your body to acclimatize with gradual exposure to the increasingly hypoxic environment; if you were to shortchange the gradual decompression and simply helicopter to the summit of Aconcagua without the use of supplemental oxygen, you would likely lose consciousness and die in short order. (Take a look at this great infographic.)

At the same time it IS true that spending time up high comes at a cost: with difficult sleep, decreased appetite, sub-optimal recovery, and lower-quality workouts it is difficult to maintain the high level sea-level cardiovascular fitness that you would have gained from following a robust training program. Atrophy is also a concern.

That said, finding the correct balance is critical. I have no data to back up this claim other than personal observations over the course of more than a decade of high altitude work, but I firmly believe this: it is lacking acclimatization rather than high-altitude-induced “de-training” that is the performance-limiting factor for the vast majority of high altitude climbers. I believe that it is unlikely that the decrease in fitness that you may experience from being up high will offset gains made by incremental acclimatization – unless you are entirely unable to sleep at high altitude, or you are pursuing elite performances up high in the category of the cutting edge records set by Kilian Jornet, Karl Egloff, or Tyler Andrews.

Once again we come back to the same lesson: all else being equal, building superior cardiovascular fitness and strength prior to prolonged exposure to high altitude builds a foundation that allows you to stay at high altitude for longer with fewer deleterious effects than you would experience if you were to approach high altitude with less fitness. Your pre-expedition training is the equivalent of making deposits into your expedition bank account. Once you are on an expedition, there are no more deposits to be made – now you are looking to spend as thriftily as possible, minimizing the effort you expend on any given day so that once you are in position for “the big effort” (your summit push, technical route, or speed record) you have as much money left as possible and can spend freely.

STORY TIME. In 2017 I set the women’s speed record on Aconcagua’s normal route from basecamp to the summit, completing the ~9,000ft ascent in 8 hours and 47 minutes. While I am a seasoned and enduring ultra runner, I am not a fast runner - yet I was able to reach the summit faster than the previous record holder local Argentinian guide Chabe Farias. I was also faster than Fernanda Maciel, elite Ultra Runner for the North Face, who IS a fast runner. Why? Because I spent weeks acclimatizing at or above 18,000ft. Similarly, I was able to best the previous men’s winning time on China’s high-altitude 100km TransQilian race course by more than 4 hours in 2019 - because I had spent weeks acclimatizing to the 10,000-14,000ft level.

The practitioner’s approach

Without prior experience at extreme high altitude it is difficult to internalize the takeaways from the above. I know that fully well, having made several extremely poor choices in my early days of high altitude climbing. Back then, I myself could have been that French runner in Gyele that you read about earlier.

Before I became a guide, I lived through two ridiculously and unsafely compressed high altitude itineraries. During my first high altitude expedition in Nepal I was lacking acclimatization so sorely that I attempted to crawl the final 50 yards to Island Peak’s summit and was lucky that I didn’t pass out in the process; back then I didn’t know enough to even begin to comprehend just how dangerous a situation I had put myself in. On my next high altitude expedition to Ecuador my then-boyfriend drew up an itinerary that packed two 14,000 foot acclimatization summits and four (!!) 19,000-20,000 foot peaks into a mere thirteen days, on a trip that I launched onto from my home in sea-level Texas and with no pre-acclimatization. Needless to say, I turned around on all but one of the high altitude peaks, triggering thankfully nothing worse than a serious personal crisis as I acutely lost faith in my identity as a mountain athlete.

Surviving those early lessons, and having gained a lot of experience since my first forays into high altitude, here are the simple steps that I now know to follow as a practitioner:

  1. Train well at home prior to your high altitude expedition. The fitter you are, the fatter your expedition bank account, the more likely your success.
  2. Build in all the time for acclimatization. Spending MORE time than average on any given expedition is a sign of expertise and well-researched strategy; it is not an indication of weakness or inexperience.
  3. Pre-acclimatize if possible. Access to elevations of 8,000-14,000ft in the six to two weeks prior to your expedition is ideal, even if just for a few days or hours here or there. If you can spend a few nights sleeping above 8,000ft, even better. If you don’t have access to mountains, consider seeking out a hypobaric training facility (altitude chamber), invest in a hypobaric tent for at-home preacclimatization, or plan a trip.
  4. Minimize your daily strain and maximize recovery once your expedition starts, within the context of covering the ground you need to cover each day to make upward progress and abide by a solid acclimatization protocol (which often includes climb-high-sleep-low acclimatization side hikes that are well worth the extra cardio effort as long as you keep your heart rate low). Watch your hydration and nutrition. Prioritize rest and sleep. Stay well within your limits. Avoid exhausting yourself.

High altitude isn’t rocket science, but it is counterintuitive. I hope this article helps shed light on some of the common pitfalls and misconceptions that we all are susceptible to.

Decidedly beyond the point of this article, but important for completeness’ sake: a word about Rapid Ascent protocols

Yes, it is it possible to climb big mountains and complete big efforts at extreme altitude without spending weeks and months on the side of said mountains – but no matter how you peel the onion, you cannot shortchange acclimatization just as you cannot bend the laws of physics.

Acclimatization has to come from somewhere, which means that the *only* way to succeed in aggressive rapid-ascent-style missions is to have pre-acclimatized in a different manner. If you want to do something huge at high altitude, your choices are to either put in the time, i.e. weeks and months, at your destination, or put in the same time – weeks and months – living and training at high altitudes elsewhere (Tyler Andrews, who moved to the Andes ahead of some of his high altitude speed records, is a great example of this). The final option is to put in weeks and months going through the painstaking and difficult work of acclimatizing at home, as Roxanne Vogel did prior to her Mount Everest speed ascent.

“[Roxanne] slept in the tent every night for three months, with a goal of spending 12hrs per day at altitude. She slept as high as 19,000ft, slightly higher than Everest base camp. ‘You’re kind of suffocating at night,’ she said.” How Roxanne Vogel Climbed Everest In Two Weeks

No matter how you peel the onion: to do big things at altitude you have to pay the price of acclimatizing which many consider a form of suffering. While I personally don’t like that terminology for an entirely elective activity, let’s stick with it for a moment because it drives home the point: The only choice that you have is when and where you suffer (at home, in training, or during your expedition) and how acutely vs how prolonged your suffering will be. The more gradual your acclimatization protocol – via a Hypoxico tent or extended mountain travel – the less acute it will feel like suffering though your bank account, career, and social schedule most certainly will feel the suffering. The less gradual your acclimatization protocol, the more acute and potentially dangerous your actual physical suffering becomes. At the end of the day one thing is clear: if you choose to pursue big objectives at altitude, suffer you will – no matter what.

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