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How to prepare for a high altitude trek

Altitude sickness can be dangerous if not caught early. To safely venture above 8000 ft, trekkers need to know how to mitigate the risk.

hikers at altitude

No scene encapsulates adventure quite like a row of snow-covered peaks, and almost every avid hiker aspires to trek in the high Andes or Himalayas at least once in their lifetime. But, high altitudes pose challenges that you just don’t experience closer to sea level, and if you plan to trek at an altitude above 2500 m or 8000 feet, you have to make certain preparations that just aren’t necessary at lower elevations. Besides making every step harder, thin oxygen-poor air poses a number of risks, and altitude sickness can be particularly dangerous if not recognised and treated early. To properly prepare for this risk, trekkers need to know how to lower their chances of experiencing altitude sickness, how to recognise its symptoms, and what to do if they start to show signs of this condition.

Altitude sickness

Altitude sickness comes in three forms: acute mountain sickness, high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE). Acute mountain sickness – the milder of the three – can develop into HAPE and HACE (both potentially fatal) if not treated in time.

Acute Mountain Sickness

Many people experience the milder symptoms of acute mountain sickness (AMS) with signs including breathlessness, headaches and nosebleeds. However, if the condition worsens, a person will experience more serious symptoms:

  • coughing
  • persistent and severe headaches
  • loss of coordination
  • disorientation

Any of these should be considered a sign to stop climbing. The only way to stop the condition from worsening is to stop at your current altitude or, in some cases, to descend. Mild AMS symptoms usually subside in two to four days.


If a trekker does not stop ascending when they start to show signs of AMS, the condition can develop into high altitude pulmonary edema (HAPE), a life-threatening type of altitude sickness that results from a buildup of fluid in the lungs. This buildup prevents proper oxygen exchange and puts the body in a hypoxic (oxygen-deficient) state. On top of the symptoms of AMS, HAPE symptoms usually include shortness of breath even when resting, a dry cough, a tight chest, and a feeling of suffocation at night. But you can also suffer the effects of HAPE without any of the symptoms of AMS. HAPE symptoms usually aren’t obvious until after two days at a certain elevation, a good reason to take acclimatisation stops. HAPE requires immediate descent and a rapid evacuation.


High-altitude cerebral edema (HACE) is the rarest and most severe form of altitude sickness. It involves the swelling of the brain as a result of fluids leaking into the brain. HACE symptoms include decreased coordination, disorientation, confusion, memory loss, irritability, and severe headaches. Like HAPE, HACE develops as a progression of AMS. If a mild case of altitude sickness worsens, it is essential that the person descends to a lower altitude. HACE requires an immediate descent of at least 1000 meters or until symptoms improve. Anyone experiencing HACE should exert minimal activity and must be accompanied when descending.

seven summits

Who is at risk?

Unfortunately, it’s difficult to know whether you are likely to suffer from altitude sickness. Age, sex, and physical fitness are not factors (even though you still need to be fit to complete a challenging trek). However, if you have suffered from AMS before, you are more likely to experience it again. Other factors that can raise your risk of altitude sickness include living at sea level and pre-existing medical conditions.

  • Previous experience of altitude sickness
  • Living at sea level
  • Pre-existing medical conditions

Need to know

Check up

Before you commit to a trip and start a training program, you should see your doctor to ensure you don’t have a pre-existing condition that would make high altitude trekking dangerous. If you are generally an active person, you’re probably good to go, but it’s always better to be certain. Also, if you intend to use Diamox, you will need to get a prescription from your doctor (But first read the paragraph on drugs).

Dexamethasone and Diamox

Dexamethasone, otherwise known simply as dex, is as popular as it is controversial. Because it inhibits cerebral swelling, dex can be a life-saver for climbers who start to show signs of edema. However, over the past two decades, mountaineers have discovered that dex can act as a performance enhancer during an ascent. And this is where the trouble starts – there are at least two dangers in taking dex prophylactically.


Firstly, dex masks HACE symptoms and reduces the drug’s efficacy in the event of emergency; and, secondly, it impairs a person’s immune system if taken for more than a week. For a more detailed description of the risks associated with dex, read Outside Online’s article. If you want to take something to help prevent altitude sickness, Diamox is much safer than dex and has proven itself as a prophylaxis.


Regular travel insurance often won’t cover high altitude trekking, and it's important to check that your intended insurance covers you for the highest point of your trek. The right kind of cover will probably be more costly than regular travel insurance, so it could be more cost effective to get trekking insurance for only the period that you will be trekking and use travel insurance to cover the days you’re not in the hills.

Months before a trek

Proper preparation can start months before a trek and even before you book flights and apply for visas. Yes, some people might just do a few hikes leading up their treks, but thorough preparation would make their experiences less arduous and more enjoyable.

Early acclimatisation

Not everyone has a 3,000 m peak at the edge of their hometown, but if you do, you should definitely take advantage of it. There’s no better way to prepare for a high altitude trek than by hiking at altitude regularly (even an altitude of 1500 m or 5000 ft will cause physiological adaptation if you are coming from sea level). But ease into it, increasing the distance and altitude of your hikes with each week of training. Your lungs and legs need a chance to become accustomed to each new level of altitude.

Physical training

In addition to preparing for the risks of altitude sickness, you’ll need to raise your fitness level so that muscles can cope with the thinner air. If you are not already very fit, give yourself two months for training. This is especially important if you plan to hike at altitudes over 4000 m or 13,000 feet. In preparing your body for the stresses of a high altitude trek, you will need to improve your stamina, condition your muscles to use less oxygen, and increase your maximum oxygen uptake – VO2 max.

group of hikers

To improve your VO2 max and make your muscles more oxygen efficient (fitter), the best exercise is interval training. This method trains the cardiovascular system by elevating the heart rate and then allowing it to recover only briefly before getting your heart rate up again. Without a full rest between sets, the cardiovascular system is forced to adapt to the stress of limited oxygen levels. When training for a high altitude trek, you will want to practice this protocol while running hills (or stairs), as this exercise will mimic the most strenuous type of hiking. When this gets too easy, you can up the ante by adding a weighted pack (again, this will more closely replicate what you’ll experience on a trek).

Breathing exercises

At high altitude it’s possible to find yourself breathless after just a small burst of exertion. Hikers who experience this feeling for the first time may get a little panicky, which only prompts faster but shallower breathing. By practising deep breathing exercises before your trip, you can better prepare yourself to get your breath under control if you start acting like a guppy. Concentrate on breathing deep in a steady rhythm. Once you’ve mastered deep breathing in a state of repose, practice it during your training hikes.

Shortly before a trek

Last minute pre-trek acclimatisation

If you don’t have any areas of high elevation close to where you live, the next best thing is to spend a few days at moderately high altitude on arrival at your destination before starting your trek. Towns like La Paz and Namche Bazaar lie above 10,000 ft and are good places to spend an acclimatisation stop before starting a trek. Taking a break for a few days will also allow you to overcome jet lag if you have crossed several time zones and are still feeling a bit out of it. And you don’t have to be idle. A few easy day hikes can help with acclimatisation. Just listen to your body and don’t overdo it.

Water intake

At altitude you need to drink a lot more water regardless of your level of exertion. Humidity is lower at higher altitudes, and sweat evaporates faster and often without you noticing. The thinner air also means that you breathe faster and so lose more water through respiration – in some cases two times faster than at sea level. As a result, you’ll need to drink up to twice as much as you’re used to. You can get your body used to this level of water intake by getting into the habit of drinking water frequently in the weeks before your trek.

mountain town

During a trek

By the time you lace up your boots, you will have hopefully laid the groundwork needed to give you the best chance of a safe and successful trek, but don’t let your preparedness lull you into a false sense of security. You still need to take the necessary precautions that will ensure that your body has time to get used to the increasing elevation.

Pace yourself

This might sound obvious, but maintaining the right pace will be very important, especially at higher altitudes. Accept that you will need to go slower than you’re used to, and then you will still need to take breaks frequently. It also helps to focus on a steady breathing rhythm. Think long, deep and slow breaths. If your breathing becomes short and shallow, slow down mentally and physically. Your pace should be relaxed enough for abdominal breathing. This is where those breathing exercises will really pay off.

Sleep low

Sleep is essential for recovery and lowering the risk of altitude sickness. To ensure a good night’s sleep, it’s recommended that you sleep at a lower altitude than that day’s high point. If your route takes you steadily uphill, you might want to continue past your accommodation after dropping your pack and take a short uphill hike before returning back to your camp or lodgings for the night. Many people find that the lack of oxygen makes it difficult to sleep at altitude, but you should at least try to doze or nap if a proper slumber proves unlikely.

Acclimatisation stops

The best way to avoid altitude sickness is to take it slowly, a precaution that becomes increasingly important the higher you go. Once above 3,500 meters, you should increase the altitude at which you sleep by no more than 300 meters a day. And even this might not be enough to ward off AMS. To ensure that your body has sufficient time to adapt to the thinner air, it’s recommended that trekkers take an acclimatisation day every three days or so. An acclimatisation day isn’t a rest day. It’s a chance to get used to the thinner air, and a short day hike to a slightly higher elevation can help prepare you for the next day’s ascent.

Acclimatisation stops


Stay hydrated and properly fueled

Staying hydrated is one of the best ways to mitigate the risk of altitude sickness, and it’s important to drink regularly even if you don’t feel thirsty. Aim to drink twice as much as you would at lower altitudes. That can mean drinking up to 4 litres a day or 220 ml every hour. By drinking this much water, you will run the risk of hyponatremia (low blood sodium levels) so it’s a good idea to take an electrolyte supplement. You will also need to up your calorie intake as you'll be burning energy at a faster rate. To keep your glucose and glycogen levels topped up, snack on carb-rich foods which will be easier to digest when exercising.

Avoid alcohol and other recreational drugs

Avoid alcohol, sleeping pills, and narcotics as these can lower your respiratory rate. If your respiratory rate falls, so will your oxygen levels. Alcohol will also contribute to dehydration, which you really don’t need. Wait till after your trek for a celebratory beer or two and then practice moderation.

More on hiking & trekking

Now that you know the fundamentals of high altitude trekking, you’re hopefully in a better position to start planning and preparing for your first high altitude trek. But don’t stop reading here. On this blog you’ll find many more articles related to hiking and trekking. You want to know how to choose a stove that will perform at altitude or why you might want to hike in shoes instead of boots? You’ll find the answers to these and other outdoor related queries in the sections on Hiking & running and Outdoor life. Happy reading.