Success Factors for Climbing Mount Everest and Other 8,000-Meter Peaks

Normobaric hypoxic training has been around for at least 30 years, I experimented with it on myself extensively in 2002 and 2003. Not much changed during most of that time. But recently it has come to our collective attention that people seem to have unlocked some variables that appear to make it work like it’s always been promised to work. But the tricky bits are that 1) the response is highly individualized and 2) while we are much closer to understanding how to tweak the exposure time and the simulated altitude, we still do not fully understand the causal relationships within the individual responses. That’s actually exactly what coach Martin Zhor and his professor are working on trying to figure out as part of their ongoing research and Martin’s post-graduate research.  We are not quite ready to share what we’re learning with the general public until we have a better understanding of the forces at play, and how to best use them. Stay tuned for more soon. Steve House

 

Education about the best way to train for 8,000-meter peaks like Mount Everest and other high-altitude mountains is a cornerstone of why Uphill Athlete exists. Uphill Athlete has coached and advised dozens of successful Everest summiters since 2015, including Everest guides, guided climbers using oxygen, independent climbers using supplemental oxygen, and a handful of climbers not using supplemental oxygen.

As of 2022, Dr. Monica Piris has completed 25 expedition as a Himalayan expedition doctor. Of those expeditions, 21 have been to 8,000-meter peaks, with 16 to Mount Everest alone.

Steve House and Scott Johnston also contributed to this article

11 Factors of a Safe and Successful High-Altitude Climb

To start off, we have compiled a list of what we consider to be the 11 primary factors that contribute to a safe and successful climb of a very high peak, ranked in order of importance:

1. Deep mountaineering experience (or a guide)
2. Good health throughout the expedition process
3. Supplemental oxygen (if chosen)
4. Aerobic fitness
5. Favorable weather, especially temperatures and wind
6. Favorable conditions on your chosen route
7. Intelligent nutrition and hydration adapted to the unique situation of high altitude
8. Movement efficiency
9. Equipment
10. “Pre-acclimatizing” in a normobaric hypoxic sleeping system, sometimes called an altitude tent
11. Training in a normobaric hypoxic environment, either with an altitude mask or in an altitude room

A History of Fast Ascents of 8,000-Meter Peaks

We have not done, nor will we do, a full review of the history of fast ascents of 8,000ers, but such ascents are not a new phenomenon. To check his facts, Steve called several alpinists, including Reinhold Messner, Peter Habeler, and Marko Prezelj. All three confirmed that, in their words, “many climbers” scaled 8,000ers on shortened time frames in the past, especially peaks in Tibet. Bagging 8,000ers was actually much more popular in the past than it is now, notably during the height of the race to climb all the 8,000-meter peaks. These days more attention is focused on Everest. Looking back to the 1980s, we saw the following ascents over a short five-year period:

• 1983: Erhard Loretan climbed three 8,000-meter peaks—G1, G2, and Broad Peak—in 17 days.
• 1984: Reinhold Messner and Hans Kammerlander linked Gasherbrum II and Gasherbrum I without going down to base camp.
• 1986: Jean Troillet and Erhard Loretan climbed the Hornbein couloir on Everest in 43 hours roundtrip.
• 1987: Alejandro Randis climbed from Plaza de Mulas to Aconcagua’s summit in 8 hours 7 minutes, and later that same year Lito Sánchez set a new fastest known time of 6 hours 32 minutes.
• 1987: Anatoli Boukreev climbed Peak Communism (7,400 m) from 6,600 meters in 1 hour 27 minutes and Lenin Peak (7,134 m) from base camp (4,200 m) in 8 hours.
• 1987: In a selection race on Mount Elbrus, Anatoli Boukreev ran from an elevation of 4,200 meters to 5,200 meters in 1 hour 7 minutes.
• 1988: Marc Batard climbed the southwest pillar on Makalu (8,481 m) solo in 18 hours.
• 1988: Marc Batard climbed Everest in 22 hours 29 minutes.

Many of the above accomplishments still stand as fastest known times today, over 30 years later. Not one of these climbers utilized anything more than mountain experience, good health, and aerobic fitness achieved through simple training methods.

A coaches’ observations on the Use of Normobaric/Hypoxic Tents and Intermittent Hypoxic Training

Over the past 7 years Uphill Athlete coaches have worked with many clients who have used the Hypoxico tent for pre-acclimatization. I have also coached one athlete who uses the Hypoxico generator and face mask while running and hiking on an incline trainer or cycling on a stationary bike.

Following are some of my observations as a coach:

• Spending 8 hours/day sleeping at a simulated altitude in a Hypoxico tent does not give as good results as natural acclimatization. This was demonstrated by two climbers last year on Everest. One acclimated naturally in the Khumbu valley for 3 weeks.  The other slept at simulated altitude in a tent for over 4 weeks.  When they met in Everest Base Camp the naturally acclimated climber was noticeably better acclimated despite the Hypoxico acclimated climber normally being faster at any altitude.
• Where the use of a Hypoxico tent is most beneficial is when the climber needs to hit the ground running at an altitude he or she is not acclimated to. Such as a Florida based climber headed to Denali or flying in to Lukla.
• Almost everyone sleeping at simulated altitude will see slower and less complete recovery from training sessions. The ramp up in training load during the final weeks before an expedition also correspond with the weeks when the simulated altitude will be the highest and the recovery the most impacted.  This needs to be clearly explained to the client.
• Hypoxico offers input on rate of ascent to their clients. But you will also want to be monitoring their recovery.
• Monitoring recovery status will be critical in order to balance the training and acclimatization protocols. A simple morning resting heart rate (wrist based) and blood O2 saturation level will be useful.  Establish a base line before the climber begins the ‘acclimatization’ process.  O2 sats in the mid 80s combined with a RHR rise of more than 10% will almost always be accompanied by obvious fatigue.  Those days should have light aerobic training in Z1 only.  Consider sleeping 1000ft/300m lower that night.  After a particularly tough workout (TSS > 20% higher than the last 4 weeks running TSS average drop 3000ft/1000m to allow better sleep.
• Where the use of a Hypoxico is not going to give as much benefit is when the climber will do a normal acclimatization schedule on the mountain and is already acclimated to the starting altitude. For example: a Colorado climber headed to the West Buttress of Denali or flying to Lukla on the way to climb Everest with the normal acclimatization rotations.  In a case like this there would be no benefits form the Hypoxico weeks later when the climber gets to those higher altitudes.  Any pre-acclimatization would have ‘worn off’ by that time.

Intermittent Hypoxic Training Observations

• There is minimal to no pre-acclimatization benefits from spending a hour three times a week on a treadmill at simulated altitude. The time exposure is too short to trigger acclimatization adaptations.
• There does seem to be some sort of benefit however. I hypothesize that the benefits come from increasing the aerobic capacity and economy of the ventilatory muscles.  This group of muscles can require about 20% of the cardiac output when working hard.  The conventional way to work those breathing muscles hard is to do high intensity work.  Breathing hypoxic air while exercising at a moderate hiking speed on a treadmill or cycling on a stationary bike will produce a very high ventilatory rate and depth as if one was doing a HIIT session.  However, the legs will not be working hard at all. Hence, there is much less global fatigue generated but those all-important ventilatory muscles will be get a strong training stimulus for aerobic adaptation.
• Even low rates of work at high altitudes will have a climber breathing like she is doing an interval work out of 400m repeats on a track. With the above mentioned hypoxic treadmill hiking session the climber is simulating the demands of breathing at high altitude but without the high intensity that would be required to get the same high ventilation rate.
• I have only used this with one very fit professional climber but with excellent feedback. In his case this is done for about 1 hour 2-3 times/week.
• That professional climber never pre-acclimates in a Hypoxico tent but feels that the intermittent hypoxic training has benefited him when he goes to altitude and starts a natural acclimatization program.

Supplemental Oxygen

Big mountain experience and good health are the foundations of a successful climb, but beyond those cornerstones, the next most powerful driver of success on very high summits is the use of supplemental oxygen. This has changed a lot in recent years: since 2012, oxygen masks have been refined and reengineered to be capable of delivering flow rates as high as 6 liters/minute. That is a 300 percent gain over the traditional 2 liters/minute flow rate.

It is important for people to understand that guide services selling compressed acclimatization schedules or “lightning ascents” rely heavily on high-flow supplemental oxygen (6 L/min) during the climb. This is fine, assuming it’s always available. We want to emphasize that, as a climber, you must stay aware of your supply of supplemental oxygen throughout the climb and descent because to run out unexpectedly could be life-threateningly dangerous.

To illustrate the importance of oxygen, consider this thought experiment: an aerobically trained climber with a high flow rate of supplemental oxygen and a guaranteed supply could probably climb Everest in a single day coming directly from sea level. If that doesn’t make the power of supplemental oxygen clear, we don’t know what could. The exact flow rate that would allow this will vary among individuals, based primarily on their lung volume, body mass, and aerobic capacity. But clearly in this hypothetical case, the more oxygen the better.

Dr. Piris is confident in this:

“YES. I would put money on it. You [Steve House] could fly from home today, walk to around about 6,500 meters without getting sick, and then put high-flow oxygen on and be successful. You might underperform compared to what you are used to, then again you might realize how easy it is when you’re sucking 6 liters/minute. But I’m close to 100 percent certain you would succeed. As far as we understand things today, the only significant and dangerous effect of the decrease in pressure is its effect on oxygen availability. There are probably some other things going on that relate directly to a sudden change in barometric pressure, but we don’t really know what they are, and it seems that none of them would kill you.”

How Supplemental Oxygen Works

To understand this a bit better, it helps to take a little diversion into how using supplemental oxygen functions. Despite the newer, better masks, oxygen equipment is unbelievably inefficient. The masks are an open circuit whereby inspired gas is a mixture of ambient air, the pure oxygen coming from the cylinder (this flow rate is defined in liters per minute), and whatever oxygen is still in the reservoir of the mask after the last inhalation. Some of this precious O₂ is captured in the reservoir, and the rest is lost. This all means that, to some extent, every breath is going to be different. If you’re sitting on Mushroom Rock resting, your rate and depth of breathing go down, so proportionally more of the volume of each breath comes from the bottled oxygen. In other words, you “decrease your altitude” a lot. When you start moving again, rate and depth of breathing increase, so more of the volume of each breath comes from the rarefied ambient air.

Therefore, it follows that for a small, light person with a lung volume of 4 liters, a large proportion of each breath will be filled by the pure oxygen. For a large person with big lungs and a max inspiratory capacity of 6–7 liters (or more), proportionally much more of each breath will be full of the rarefied high-altitude air because each breath is a relatively large volume and the flow from the bottle is simply not enough to make up the difference. So flow rates affect different people differently based on their individual bodies, their aerobic fitness, and their exertion level at any given moment.

Mask Altitude Calculations

Dr. Tom Hornbein, who famously made the first traverse of Mount Everest in 1963 via the West Ridge to the South Col, climbing with Willi Unsoeld as part of the large 1963 American Everest Expedition, worked with Bill Sumner to make the above calculations back in 1962. They were trying to estimate the “Mask Altitude” of different oxygen flow rates at different levels of work. As we know from our above discussion, these are averages with significant individual variation.

For a climber receiving a flow rate of 4 L/min while working maximally on the summit of Everest, they estimate a Mask Altitude equivalent to 7,200 m/23,600 ft—a drop of approximately 1,900 m/6,200 ft. For a climber at rest, they estimate a Mask Altitude of approximately 3,200 m.

Reprinted with Permission of Dr. Hornbein

Supplemental oxygen use can certainly make up for a lot. Both Steve and Dr. Piris have seen people who are shockingly unfit to summit Cho Oyu, Makalu, Everest, and other high peaks easily on high-flow-rate oxygen combined with near-constant sugary foods. (Tip: Energy chews work a lot better than gels with the masks.)

That said, choosing to utilize supplemental oxygen at high altitude is not a good argument against proper physical preparation. Highly trained bodies utilize their supplementary (and naturally available) oxygen to a much greater effect than untrained individuals, thereby making them warmer, faster, and safer on summit day.

Aerobic Capacity

We know from extensive personal experience, both with ourselves and with the climbers Uphill Athlete has trained, that behind supplemental oxygen use, the next most important factor for success is aerobic capacity. Put simply, aerobic capacity is your body’s ability to turn oxygen into locomotion.

It is also the piece of the training puzzle that we have the most control over as athletes and coaches. Uphill Athlete has developed some useful guidelines for how fit a mountaineer needs to be—based on direct observations and the medium-term (4-to-6-month) training data of various climbers—in order to reasonably expect to be able to climb a mountain like Denali, Aconcagua, Cho Oyu, or Everest. Jump to our article: Fit to Climb Everest.

Lacking that data, a climber can do a lab test to determine both Aerobic Threshold (AeT) heart rate and Anaerobic Threshold (AnT) heart rate. Once you know those heart rates, it is a simple calculation to find the ratio between the two: 1 minus AeT/AnT. If you’re fit, your Aerobic Threshold should be within 10 percent of your Anaerobic Threshold. A spread between these numbers that is greater than 10 percent indicates that significant aerobic capacity gains are still to be had via proper training methods. From this, it should be very clear that a high-altitude climber’s primary focus should be on maximizing aerobic capacity.

Localized muscular endurance is another important measure of fitness. Local (in this case meaning your legs) muscular endurance is simply a fancy way of saying that you can climb, weighted, for many hundreds or thousands of vertical meters without a significant drop in pace as measured by ascent rate. This is another key capacity for a successful 8,000-meter climber and is developed by correct training methods, starting with aerobic capacity. Note that for high-altitude climbers, this ability is relevant only when performed within the climber’s Aerobic Threshold, because essentially no anaerobic work can be done at higher altitudes. Ever try sprinting at 8,000 meters? We didn’t think so.

Normobaric Hypoxic Tents and Training

Many high-altitude climbers ask Uphill Athlete about using various normobaric hypoxic training methods. Before you consider using a normobaric hypoxic tent for what some people will call (inaccurately) “pre-acclimatization,” you should understand the following:

There is currently (as of 2018) no known scientific evidence that supports the assertion that a normobaric hypoxic program works for pre-acclimatization to high altitude.

This is why we have provided, in list form, all the peer-reviewed research we have found. We will continue to add resources as we become aware of ones we’ve missed and as new publications become available.

The tents work by changing the ratio of nitrogen to oxygen in the air you breathe, not by changing the pressure.

At the end of this document, we share our recommendations for using a normobaric hypoxic tent for sleeping and why it may, sometimes, help.

Time spent in the tent has been demonstrated to be the critical factor.

Eight hours out of 24 is considered to be the minimum amount of time required to affect any adaptation. (reference) This is the one known factor that has been studied and proven consistently in multiple studies to be a crucial factor.

Some people will use “altitude masks” or “altitude rooms” for training. Due to the importance of duration, as stated above, 30–120 minutes spent in a room a couple of times a week is unlikely to induce any changes, and in fact has not been shown in any published peer-reviewed study to do so. Here is the research.

Inconsistent use of the tent diminishes the benefit.

Aim for 8 hours out of every 24 hours.

It is our experience that it is very difficult, and often impossible, for athletes to continue to train hard enough to be gaining fitness while sleeping in a tent over the approximate altitude equivalent of 10,000 feet.

This is the biggest argument against sleeping or training in a normobaric hypoxic environment. Individual results do vary significantly, however. The same factors that predispose an athlete to be quick to recover—youth and a long prior history with endurance training—have the potential to help an athlete see results through tent use. If your training is significantly impacted by the hypoxic tent use (which it frequently is, even for athletes like David Goettler and the late, great Ueli Steck, neither of whom could maintain their training loads when sleeping in these tents), then the tent will likely be a net negative.

The only published, peer-reviewed scientific evidence available shows increased sea level performance after prolonged hypoxic tent use.

This is understood to be related to increased hematocrit levels resulting from long-term normobaric hypoxic tent use. It is understood that this provides a small (along the order of 1 percent) boost in performance for competitive endurance sports at sea level. Note that due to the six weeks it takes to create new red blood cells (which is an increase in hematocrit), you need to spend a minimum of six weeks sleeping in a tent.

The lack of peer-reviewed science on this subject does not rule out that a normobaric hypoxic program may help, especially for climbs below 5,000 meters/18,000 feet.

There are many instances where athletes and coaches figure out things that work before the scientists have an explanation. This is perhaps the biggest argument for using the tents. There is significant anecdotal evidence that, up to moderate altitudes, they help people. What we have seen is that when it is possible for a climber to move from their home, where they have the normobaric hypoxic tent set up, to above 4,000 meters within 24 to 48 hours, they will acclimate more comfortably to these moderate altitudes.

Many of the biological processes of adaptation to high altitude remain unclear and poorly understood.

In recent (2017) research, Dr. Robert Roach showed that 5,000+ genes are either up-regulated (3,000+) or down-regulated (2,000+) over short-term exposure to altitude (16 days in his study). During that time frame there was no change in the subjects’ hematocrit (red blood cell) levels, yet the performance of his test subjects improved 25 percent in an uphill time trial over the 16 days. So, something unrelated to O₂ carrying capacity happened that increased performance. This is a very interesting result and may indicate that the hematocrit levels are not as important as everyone has supposed them to be. Also fascinating was the fact that the gene that showed the greatest up-regulation is the same gene that is dominant in high-altitude native populations. This gene clearly has some primary (and not yet understood) role to play in high-altitude adaptation. We can’t be sure that normobaric hypoxia does not trigger this same gene, but that is a complete unknown at this point.

The majority of Uphill Athlete’s coaching clients who have attempted 5,800-to-6,900-meter summits—usually Denali, Ecuador volcanoes, and Aconcagua—without supplemental oxygen support and who used the tents during training have NOT been successful in reaching the summits on a faster-than-traditional ascent rate schedule (for the guided climber demographic).

However, we feel these clients as a group were not highly aerobically adapted. We know through personal experience and by observing other aerobically fit climbers that accelerated acclimatization schedules can lead to successful climbs based solely on good aerobic fitness.

We strongly believe that aerobic fitness is far more important than normobaric hypoxic tent use.

Our understanding is that it is primarily guiding businesses and their clients who use the hypoxic tents to allow participants to be acclimatized to the lower altitudes of up to 5,000 meters/18,000 feet so that they can cut two weeks off their expeditions. They then administer supplemental oxygen, typically around 6,600 meters, sometimes as low as 6,400 meters. These protocols do seem to allow climbers to minimize acclimatization rotations on the mountain (again, looking for time efficiency), but we want to be clear that these strategies never improve performance. They buy time.

Hypoxic Tent Use and Professional Climbers

Several of the best mountain athletes in the world, including Kilian Jornet, Ueli Steck, and David Goettler, have used the tents and have talked about it, which we think is great. But non-professional athletes need to understand that these elite athletes 1) are professional endurance athletes, 2) know their bodies very well, and 3) have deep mountain experience. Remember, they can give good opinions about whether they think it makes a difference for them, but 99.99 percent of people are at a completely different fitness level than Kilian, Ueli, or David. We spoke to Kilian and to Ueli about how much they thought their use of Hypoxico tents had contributed to their performance, and both were very equivocal. Ueli was ready to stop using the tent as he believed his performance would remain the same. When we asked Kilian if he was certain his use of the tent before his 2017 Cho Oyu and Everest climbs was critical to his success, he said no, he wasn’t sure it had made any difference at all.

Hypoxic Tents Use and High-6,000-Meter Peaks

For climbs without supplemental oxygen, especially on high-6,000-meter peaks like Aconcagua, we have found hypoxic tent use to be the least helpful. Our data is only anecdotal, but a pattern seems to have emerged that Aconcagua is just a little too high, and perhaps the distance traveled is a little too long.

Two examples from the 2017–2018 season illustrate this point. Uphill Athlete recently started working with a woman who had climbed Aconcagua in January, and her AeT test in March revealed she had an Aerobic Threshold heart rate of 124—a clear case of Aerobic Deficiency Syndrome. Yet she was able to climb on a normal schedule, without using a hypoxic tent, and reached the summit on day 12 without any problems and feeling fine. As a contrast, Uphill Athlete worked with a man who trained for a year, held a chronic training load of over 65, and used a normobaric hypoxic tent for two months leading up to his departure for Aconcagua. On day 4 he had climbed to high camp, and then he had to descend two days later without the summit and without more time. He was much fitter than the first climber described here, but the self-imposed time restriction made what should have been an easy trip impossible.

Hypoxic Tent Use and Moderate Altitude (4,000 Meters/13,000 Feet and Below)

Uphill Athlete provides coaching and training advice to many mountain runners and ski mountaineers who compete at low or moderate altitudes. For these athletes, there is good evidence that longer-term normobaric hypoxic tent use can induce demonstrable gains in EPO and red blood cell counts, which would likely lead to improved race performance at sea level. Remember that EPO (erythropoietin) is a naturally occurring compound that stimulates new red blood cell growth; it is the synthetic version of EPO that is banned by the World Anti-Doping Agency.

Mountain runners and ski mountaineers living at low elevation and wishing to compete in high-elevation events do seem like the group most likely to benefit. These events are at moderate elevations, often 3,000–4,000 meters/10,000–14,000 feet, and many participants don’t have time to spend the two weeks prior to races like Leadville or Hardrock acclimating. If this is you, then we would recommend four weeks sleeping in a normobaric hypoxic tent while carefully monitoring your recovery from harder training.

Practical Guidelines for Hypoxic Tent Use Before an Extreme-Altitude Climb

The standard strategy for increasing “tent altitude,” or more correctly, increasing the normobaric hypoxia, is to abide by the standard ascent rate equivalent of 300 meters/1,000 feet per night. In their website information, one provider, Hypoxico, warns against sleeping at altitudes above the equivalent of 12,000 feet. However, we have known their sales associates to be quite enthusiastic in recommending higher sleeping elevations to Uphill Athlete’s coaching and expedition clients. That said, no one, even the most evangelical normobaric altitude tent user, recommends going above an approximate altitude equivalent of 4,900 meters/17,750 feet.

Conclusion

We believe that if you want to climb an 8,000-meter peak, the safest way to do so is to arrive for your expedition in the best aerobic fitness of your life and employ supplemental oxygen. We believe that for 99 percent of climbers, sleeping in a hypoxic tent prior to departure on a high-altitude expedition will return fewer gains than proper training and preparation. Remember, the 6 liters/minute of pure O₂ into your mask is probably a million times more important than the possible alterations in gene expression that may or may not be induced by normobaric hypoxia. It seems that, given the numbers accruing now (even if it’s pure placebo affect), normobaric hypoxic tent use can make the approach to base camp more comfortable in terms of ease of initial acclimatization. However, we can’t state that as fact.

Can we quantify the amount by which correct aerobic capacity training increases oxygen efficiency in order to show that a highly trained elite athlete will tolerate extreme hypoxia to a much greater degree than an untrained one, and will perform better in extreme hypoxia than an untrained climber? Not yet, but this would be helpful to determine.

Importantly, any climber who is aiming to maximize their endurance training and aerobic fitness before a high-altitude climb, and who also wants to try using a normobaric hypoxic tent, should limit tent use during the two-week taper period. We have found that this strategy is most likely to be helpful in allowing the climber to reach base camp faster and more comfortably without negatively impacting fitness. The training that happens in the final weeks before departure is difficult and crucial, and using a normobaric hypoxic tent during this time threatens to undercut any gains. Note that this approach may be problematic as the minimal rental period for some hypoxic tent providers is one month.

Collectively, we have spent hundreds of hours working on this article. We talked to everyone from the hypobaric enthusiasts to the doubters, among them current Everest guides. We know of only a handful of guides who believe in hypoxic tent use and recommend it to their clients. Believe us, if there were a shortcut to safe and effective acclimatization to high altitude, we’d be the first in line. Indeed, both Steve and Scott Johnston tried it on themselves prior to Himalayan and Alaskan expeditions in 2001 and 2002 but gave up on it then for the same reasons Uphill Athlete doesn’t endorse it now. Aerobic training, and the good sleep that adequate recovery from that training requires, is simply a better, safer, and more effective strategy for acclimating comfortably and climbing quickly and safely.

Do you have personal experience with utilizing normobaric altitude tents and generators prior to climbing (or running or skiing) at high altitude? Please write us about your experience: coach@uphillathlete.com.

FAQs That No One Can Answer (At Least Not Completely)

Q: Do the tents do anything for ANY athlete other than have a placebo effect?
A: This is unknown. No peer-reviewed science has been conducted to answer this question.

Q: Do the tents speed up the process of acclimatization—to moderate and/or high altitude?
A: Again, this is unknown as no peer-reviewed science has been conducted to answer this question. There does seem to be a growing body of anecdotal evidence that it does help people perform better at moderate altitudes. The term “pre-acclimatize” is often thrown around, and frankly, misused. Acclimatization is a precise term used in reference to the body’s natural ability to make a wide range of adaptations to high altitude. Please refer to Chapter 12, “Altitude: Climbing Higher, Faster,” in Training for the New Alpinism for a more complete discussion of altitude and acclimatization.

Q: Do the tents perhaps somehow prime the body such that it’s better prepared to acclimatize?
A: Unknown.

Q: Do the tents alter any physiological parameters, such as those associated with athletic performance and/or those associated with acclimatization to altitude?
A: Unknown.

Q: Do the tents stimulate red blood cell production before exposure to true altitude?
A: Sometimes, but not in all people. See “Acute Normobaric Hypoxia Stimulates Erythropoietin Release” on this page.

Q: Do the tents cause a measurable rise in EPO, even if not quite enough to trigger RBC production? 
A: Sometimes, but not in all people. See “Acute Normobaric Hypoxia Stimulates Erythropoietin Release” on this page.

Q: Is breathing all of that nitrogen harmful?
A: Probably not, given that we breathe lots of nitrogen. But strictly speaking, we do not know.

Q: Is the detrimental effect of sleeping in a hot, humid tent for eight weeks prior to an expedition balanced by an improved athletic performance or a perceived improvement in performance?
A: Maybe. No one knows.