Acclimatisation in the mountains and on Elbrus

Acclimatisation in the mountains is the set of changes by which the body adjusts to a lower partial pressure of oxygen. It takes time and does not come bundled with an expensive down jacket. Physical training helps you keep moving longer and recover better, but on its own it does not protect you from acute mountain sickness. A very fit person can fall ill just as convincingly, and sometimes simply reaches a dangerous altitude sooner.

Three things matter on Elbrus: the altitude of the first night, the rate at which the sleeping altitude rises after that, and how the individual reacts. A day out to a higher point followed by a return lower down is usually tolerated better than the same gain applied to the sleeping altitude. That is why a sound programme alternates ascents, descents, rest and nights, rather than simply adding numbers day after day.

The main rule of altitude: with symptoms of altitude illness, do not go higher to sleep. If symptoms get worse at the same altitude, descend and tell your guide.

How the body changes at altitude

As you climb, atmospheric pressure falls. The proportion of oxygen in the air stays roughly the same, but its partial pressure drops, so every breath makes less oxygen available to the body. Over the first hours and days, lung ventilation increases and heart rate, fluid balance, sleep and blood flow all change. According to CDC Yellow Book 2026, the most important acute phase of acclimatisation takes the first 3-5 days, though further changes continue for weeks and months.

The familiar story that the body will “grow a lot of red blood cells” in the first two days hurries the biology along too fast. In early adaptation the key role is played by increased breathing and the changes that go with it. A rise in red cell mass belongs to longer-term adaptation and will not rescue a week-long route taken too quickly.

Why sleeping altitude is counted, not only the highest point reached

A short day out higher up, followed by a return to a lower place to sleep, creates a hypoxic stimulus while letting the body recover lower down. A night fixes a long exposure to altitude, and it is often after the first night that symptoms show. Two routes with the same maximum altitude can therefore have completely different acclimatisation profiles.

The CDC, citing the recommendations of the Wilderness Medical Society, advises avoiding a rapid ascent straight to a high first night where possible. Above 3000 m the guide figure for travellers is an increase in sleeping altitude of no more than about 500 m per day, plus an extra night for every 1000 m of sleeping altitude gained. That is a general medical framework, not a literal scheme for every mountain: the terrain, the transport and the particular route may call for different tactics.

Acclimatisation on Elbrus in the different programmes

Before you decide, compare all the Elbrus programmes. If this is your first experience above 5000 m, the nine-day south usually leaves a calmer margin than a shortened programme. Getting up quickly by cable car is technically easy; acclimatising quickly at the push of the same button is not yet available.

Acute mountain sickness: what counts as a symptom

Acute mountain sickness usually appears after a recent gain in altitude. Headache is the typical symptom and may come with nausea, loss of appetite, dizziness or marked fatigue. Disturbed sleep at altitude is common, but in the updated Lake Louise score it is no longer used on its own as a diagnostic sign of AMS.

Similar complaints are caused by dehydration, chilling, overexertion, infection, migraine, alcohol, problems with food and other conditions. A diagnosis is not made from a single message in a group chat and a single saturation reading. It is the climber’s duty to report symptoms to the guide rather than hide them for the sake of the summit.

Signs that call for immediate descent and assistance

• loss of coordination, an unsteady walk;
• confusion, unusual behaviour, marked drowsiness;
• breathlessness at rest;
• a sharp drop in capacity, increasing difficulty breathing;
• symptoms worsening while resting at the same altitude.

High-altitude cerebral oedema and high-altitude pulmonary oedema are life-threatening conditions. The basic tactic is to stop climbing, minimise exertion and organise an urgent descent; oxygen and drug treatment are used according to protocol and do not turn continuing the ascent into a good idea.

What a pulse oximeter shows

Oxygen saturation at altitude is naturally lower than at sea level. What is useful is not a magic “normal figure for everyone” but the trend of readings at rest, taken together with symptoms, altitude and general condition. Cold fingers, movement, bright light, a weak signal and a badly seated sensor all distort the result. The WMS recommendations warn specifically that clinical decisions must not be based on small differences between individuals or between consecutive readings.

1. Warm your hand and take off any thick glove.
2. Sit down and breathe calmly for a few minutes.
3. Seat the sensor firmly and wait for a steady signal.
4. Write down the altitude, the time, the pulse, the saturation and the symptoms.
5. Do not treat the number apart from the person.

Why good fitness does not guarantee acclimatisation

A trained person moves more efficiently and usually copes better with sustained work. But an individual tendency to altitude illness is not determined by fitness alone. Indeed, a strong participant sometimes increases the risk by going too fast, hiding symptoms and treating fatigue as somebody else’s problem. The CDC states plainly that physical fitness does not determine susceptibility to altitude illness.

Preparation is still necessary: it lowers the ordinary load on the body and frees up reserves for cold, altitude and a long descent. Endurance and acclimatisation simply serve different purposes.

Water, food and sleep

At altitude you lose more fluid through breathing, but there is no need to force down excessive volumes of water: overhydration does not speed acclimatisation and can be dangerous. The markers are ordinary thirst, regular drinking in small amounts, and the colour of your urine, without trying to make it colourless at any cost. Anyone with heart or kidney disease or a disorder of fluid balance should be advised by a doctor.

Appetite can fall, so it is best to know in advance which foods you can eat in cold and at altitude. Alcohol in the first days of acclimatisation worsens sleep and can mask or intensify symptoms. Sleeping tablets and sedatives must not be chosen on the advice of the next person in the hut: some of them suppress breathing.

Do you need medication to acclimatise?

Acetazolamide has proven uses in preventing and treating certain forms of altitude illness, but the decision depends on the risk profile, contraindications, other conditions and other drugs. It is not a substitute for a sound schedule and it gives no licence to keep climbing when things get worse. Whether to use it, and how, is discussed with a doctor before the trip.

Dexamethasone and the drugs used for high-altitude pulmonary oedema belong to medical tactics, not to a tourist’s just-in-case kit. Publishing universal dosages without a history, and teaching self-medication through an article, would suit nobody but the illness.

Does pre-acclimatisation help?

Spending at least two nights above roughly 2750 m shortly before the trip can lower the risk compared with arriving straight from the lowlands. The closer that exposure is to the main programme, the more useful it is. A one-off session in a hypoxic mask does not imitate a drop in atmospheric pressure. Normobaric hypoxic training can be used under a specific protocol, but it does not replace real time on the route.

Typical acclimatisation mistakes

• Arriving after the group and trying to “catch up” on altitude.
• Choosing the shortest programme simply because you are a good runner.
• Racing the pace on the first outings.
• Hiding a headache and nausea from the guide.
• Going higher to sleep while symptoms persist.
• Treating a low saturation reading as the whole diagnosis or, the other way round, ignoring symptoms because of a “good number”.
• Taking a medicine for the first time on the mountain without discussing it with a doctor.
• Trying to make up for too fast an ascent with litres of water, energy drinks or force of character.

Scientific sources

• CDC Yellow Book 2026: High-Altitude Travel and Altitude Illness
• Wilderness Medical Society Clinical Practice Guidelines: 2024 Update
• The 2018 Lake Louise Acute Mountain Sickness Score
• UIAA Medical Commission: Mountain Medicine

This material is educational and does not replace a consultation with a doctor. If you have a chronic condition, are pregnant, have had a previous severe episode of altitude illness or take medication regularly, discuss the trip with a specialist in altitude or sports medicine.

The original detailed article

Acclimatisation in the mountains: how to prepare your body for altitude

High mountain regions draw travellers and climbers with their beauty and their challenges. Before an ascent, however, you have to attend to the single most important thing: acclimatisation. Adapting the body to less oxygen in the air is vital if you are to avoid serious consequences such as mountain sickness.

What acclimatisation in the mountains means

Acclimatisation in the mountains is the process by which the body physiologically adapts to the reduced partial pressure of oxygen found at altitude. At sea level oxygen saturates the blood easily, but above 2500 metres its concentration falls sharply. That can cause hypoxia, a state in which the tissues and organs are deprived of oxygen.

Effective acclimatisation lets the body adjust to the new conditions: breathing and heart rate increase and the number of red blood cells rises, which improves the transport of oxygen around the body. Without acclimatisation, climbing to a significant altitude risks problems such as headache, nausea, weakness and even cerebral or pulmonary oedema.

The principles of successful acclimatisation

1. Gain altitude gradually. Never gain altitude abruptly. The body has to adapt in stages, which gives the physiological changes time to happen.
2. Rest periods. For every 600-800 metres of altitude gained you need to spend at least one night at the height you have reached.
3. The rule of “climb high, sleep low”. Going high during the day and descending to sleep helps the body get used to the reduced oxygen faster.
4. Eating and drinking properly. Dehydration makes the symptoms of mountain sickness worse, so drinking water, tea or isotonic drinks is the key to success.
5. Avoid overexertion. In the first stages of acclimatisation it is important to avoid intense physical effort.

Mountain sickness: how to avoid complications

Without acclimatisation in the mountains, mountain sickness develops. Symptoms can appear within a few hours of gaining altitude. They include:

• headache;
• insomnia;
• loss of appetite;
• weakness and fatigue.

If the symptoms intensify, an immediate descent to a lower altitude is needed. Ignoring the body’s signals can lead to acute conditions such as pulmonary or cerebral oedema.

The role of acclimatisation outings

Acclimatisation outings are ascents to altitude followed by a return to base camp to sleep. Approaches like this are particularly effective when preparing for expeditions to significant altitude, Elbrus among them. Each outing stimulates the body to produce erythropoietin, the hormone responsible for increasing the number of red blood cells.

Acclimatisation on Elbrus

Elbrus, the highest summit in Europe, demands particular attention to preparation. Proper acclimatisation on Elbrus is a key element of a successful ascent. Above 5600 metres the air becomes extremely thin, and without preparation the reduced oxygen can become a serious obstacle.

Acclimatisation on Elbrus usually proceeds in several stages:

1. Arrival in the Elbrus region. The first days are spent at an altitude of 2000-2500 metres. Here the body begins to adapt to the change in the oxygen environment.
2. The first acclimatisation outings. Climbers go up to altitudes of 3000-3500 metres and return to base to sleep.
3. Going up to 4000-4200 metres. This is the critical stage of acclimatisation on Elbrus. Outings like these prepare the body for the altitude of the summit camp.
4. A rest day. Before the summit push it is advisable to set aside a day for recovery.
5. The summit push. The final stage demands maximum endurance. A prepared body copes with the effort successfully.

Acclimatisation on Elbrus works because of the natural conditions the region offers. There are many routes here for training ascents, as well as places to stay at a range of altitudes.

Mistakes in acclimatisation

For all the advice available, people often make mistakes:

• Climbing too fast. The wish to save time often leads to health problems.
• Ignoring the symptoms of mountain sickness. Some people try to deal with feeling unwell through medication instead of losing altitude.
• Not paying enough attention to drinking. Taking in water is an important part of acclimatisation, since the body loses fluid faster at altitude.

The psychological side of acclimatisation

Mental preparation matters no less. In the mountains people encounter unfamiliar fatigue and stress. A positive frame of mind and confidence in your own abilities help you get through the hard parts.

Medication

Some athletes and travellers turn to drugs such as Diacarb or aspirin, which ease the symptoms of mountain sickness. Using them without consulting a doctor, however, is not recommended.

Acclimatisation in the mountains is not merely a preparatory stage but a science in its own right. Acclimatisation done properly, on Elbrus as on other high summits, is the foundation of a successful ascent and of good health. Mountains demand respect and patience, and the right approach guarantees that every ascent is not only enjoyable but safe.