After record-breaking Everest climbers revealed they use hypoxic tents to get altitude ready without acclimatizing on the mountain, we look at how the technology works

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2 days ago

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Around 800 people attempt to climb Mount Everest each year, braving extreme conditions for the chance to say they've stood on top of the world.
Along with rigorous physical and mental training, hopefuls need to prepare for the harrowing effects of altitude atop Earth's tallest mountain, where the amount of oxygen taken in with each breath is drastically lower than at sea level.
Traditionally, climbers have acclimatized by spending significant time in the mountains, heading up and down to prepare their bodies for the dizzying heights, and reducing the impact of altitude sickness. This tried and tested method has proven effective for the past 70 years of Everest expeditions, but comes with one major drawback: time.
Without four to six weeks to dedicate to acclimatization, many Everest hopefuls are now turning to modern technology to help them prepare, sleeping and exercising in specialist acclimatizing 'hypoxic' tents, which do away with the need to spend months in the mountains.
'You sleep like garbage if you're not acclimatized, you lose your appetite, so you wither away
Brian Oestrike, CEO of Hypoxico Altitude Training Systems
As alien as it may sound, hypoxic tents, otherwise known as altitude tents, have become increasingly common in recent years, used by alpinists and climbers to prepare for harsh conditions.
This year, a group of British veterans in their forties and fifties used hypoxic tents in combination with controversial Xenon gas to speed-climb the mountain, summiting a record four days after arriving in Nepal and effectively going from sea level in London, to the highest peak on the planet in 5 days.
The very next day, US-Ukrainian climber Andrew Ushakov claimed to have broken their record, after spending over 400 hours acclimatizing in a hypoxic tent. Ushakov says he went from New York to the Everest summit in just 3 days, 23 hours, and 27 minutes.
So what are hypoxic tents, and how can they help climbers achieve these once-unthinkable feats? Read on for everything you need to know.
Put simply, hypoxic tents mimic the low oxygen levels of high-altitude environments.
The air at sea level contains 20.9% accessible oxygen, a number that drops dramatically the higher you get. At Everest base camp, it falls to around 10.4%. By the summit, it's down to just a third of the accessible oxygen quotient at regular sea-level.
In healthy individuals, blood oxygen saturation levels sit around 98% to 100% at sea level. At altitude, that number drops to roughly 87% to 92% This has a weakening effect and can cause altitude sickness.
Hypoxic tents simulate this mix with a generator or pump, which removes oxygen and replaces it with nitrogen, reducing the amount of oxygen in the air to high-altitude levels.
Sleeping in the simulated altitude conditions of a hypoxic tent triggers your body to saturate your blood oxygen levels, releasing red blood cells and ready your system for conditions at 20,000ft (6,096m).
'As you expose yourself to altitude, your kidneys release EPO [erythropoietin], which starts this physiological change that leads to an increase in red blood cells, but more so into a better ability to transport and utilize oxygen,' Brian Oestrike, CEO of Hypoxico Altitude Training Systems tells us.
Climbers like Ushakov use hypoxic tents to ready themselves for the unforgiving mountain conditions atop the globe's tallest peaks. Saturating your blood oxygen levels can be beneficial in several ways, reducing the risk of altitude sickness and preparing your body for the tiring effects of altitude.
'You improve your comfort and safety margin as you're ascending up through the mountains,' Oestrike explains. 'You sleep like garbage if you're not acclimatized, you lose your appetite, so you wither away as those things happen. By acclimatizing beforehand and using this equipment, you can offset your expedition, it improves your safety and your comfort margin.'
By mimicking arduous alpine conditions, hypoxic tents can reduce the time it takes to acclimatize.
'Most people, if they're going to the Himalayas, historically have a six to eight-week expedition itinerary,' continues Oestrike. 'It takes that long for your body to slowly adapt and build the red blood cells that carry oxygen and allow you to climb safely."
Ultra-running superstar Kilian Jornet slept inside a hypoxic tent for eight weeks before his maiden ascent of Mount Everest, mimicking altitudes of 13,000ft (3,962m) to 16,000ft (4,877m) without leaving sea level.
He then became the fastest man to climb Everest alone and without oxygen, summiting the 29,000ft (8,850m) behemoth in just 26 hours.
Although they're becoming increasingly popular with climbers and other extreme athletes, hypoxic tents do have their limitations and experts say they cannot be trusted as the sole method for acclimatization.
"It's not the full acclimatization. I would say it's the first step," says Grégoire Millet, Professor of Exercise Physiology at the Institute of Sport Sciences in Lausanne, France.
He explains that, even after months of sleeping in a hypoxic tent, "you will use some acclimatization, but not the full spectrum. You can be fully acclimatized in the tent, and not acclimatized to the real mountain".
In other words, hypoxic tents cannot fully prepare the body for the rigours and difficulties of climbing at very high altitudes. In the Himalayas, elite climbers (and paying clients) on expeditions aiming for the highest peaks enter what is known as the Death Zone, an extremely dangerous zone above 26,247ft (8,000m), where besides having to deal with temperatures potentially tumbling to -31°F (-35°C) and highly technical terrain, the oxygen in the air is so low it's impossible for humans to survive for long.
"You have to go to the real mountain for at least a few days before you travel," advises Millet, an expert in acclimatization technology.
He advises climbers to use the tents in combination with traditional acclimatization methods, like sleeping atop smaller mountains, before tackling any major peaks.
"It's better to use the tents, and then before you go to the Himalayas, it's recommended that you go for at least a few days to the Alps," he says.
He says your body acclimatizes differently at real altitude and, despite their many benefits, hypoxic tents cannot fully replicate the tough conditions and and lack of oxygen in the mountains.
It's not just mountaineers who put hypoxic tents to good use. All manner of sports people, from swimmers to footballers, use simulated altitude environments to expand their physical capabilities and access the benefits of altitude training.
'If you can transport and utilize oxygen better, that leads to better performance benefits, and literally just more ability to consume oxygen,' says Oestrike.
"Most of the elite athletes, they have a hypoxic chamber at home," adds Millet.
"It's not a tent, but it's a real chamber. It's the same idea, you decrease the oxygen concentration in the room."
By training and sleeping at altitude, athletes can increase what's known as their hemoglobin mass, which boosts the amount of oxygen they can utilize during exercise.
As Millet explains, this requires considerably more time than mountain acclimatization: "Every 100 hours sleeping in the tent, you will increase your hemoglobin by one percent."
Every member of the US Olympic rowing quad who won gold at the Paris 2024 games reportedly slept in hypoxic tents for six weeks before racing.
Although they're designed for elite athletes, hypoxic tents can be useful to outdoor enthusiasts of all abilities, helping to build fitness and intensify workouts.
When it comes to climbing, Oestrike suggests that hypoxic tents are even more useful to amateurs than professionals.
'Most people who are committed to an 8,000m (26,247ft) peak know what they're getting into, they know what the training looks like, and they know what it takes to prepare.
'High-level athletes are already training super intensively. So the person that's more modest and maybe needs to lose a little weight, they're going to see a greater upside.'
Of course, hypoxic tents are not required for easy-to-medium-difficulty ascents. Nor are they absolutely essential to climb giants like Mount Everest. Traditional, slower, acclimatization has proven itself as an effective, stress-tested method of alpine preparation.
Rather, hypoxic tents are an additional and convenient method of acclimatizing, to be used along with high-altitude climbing and intensive training.
You can read our exclusive interview with Andrew Ushakov here.
For more on climbing preparation, check out our expert guide.
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