How to acclimatise on a high-altitude trek

Taking on a high-altitude trek for your next trip is a great challenge. Insight Guides' local expert and trip planner Mark shares a few tips on acclimatising correctly and safely
Trekking to Pangboche
Trekking to Pangboche. Photo: Trip provider

Trekking to Pangboche. Photo: Trip provider

There are many destinations around the world which involve going to a reasonably high altitude: the Himalayas, the Atlas Mountains, Machu Picchu and Mount Kilimanjaro are just a few. Should you worry about taking a trip here? No, not really. But you should be aware of the effects of altitude and the dangers.

Tens of thousands of people go trekking every year and by far the majority do so without any incident of a serious nature. The human body is quite capable of adjusting to a very wide range of barometric pressures. In relation to altitude, this adapting process is called acclimatisation.

The prime example to explain this is with the local people. Using Insight Guides' Exclusive Everest trip as an example, even at the highest overnight point of your trek people live there permanently. There are even some smaller villages even higher up. Needless to say, the local people are naturally acclimatised and go about their daily business just as we would do at sea-level.

Even at these high elevations, there’s plenty of oxygen and you are nowhere near the extreme heights that mountaineers attain without the use of supplementary oxygen. The Exclusive Everest trek has been carefully planned to afford you both acclimatisation and a controlled rate of ascent.

“Climb high, sleep low”

Let's look at the trek in more detail. Your first day, after flying into Lukla, sees you descend to 2600m. For context, an aircraft cabin is pressurised to 2400m. The next day you trek up to Namche Bazaar (3440m) and the following day you have an acclimatisation day in Namche. This is because 3000m-3500m is often where the effects of altitude are first experienced and so an acclimatisation day is essential in order to allow your body to adjust.

Don't confuse an acclimatisation day with a rest day. You can, of course, rest up. Still, it’s a good idea to do some physical activity and on a trek that activity is walking. However, it’s also important not to over-exert yourself either. That can be self-defeating. So, usually, the guide will take you on a walk above Namche itself to a viewpoint and/or the local Sherpa Museum. It’s not a long walk and can be taken at a very moderate pace. 

By doing this you have followed the mountaineer's altitude mantra, “climb high, sleep low”, as you have descended back to Namche.

The next day is both ‘up and down’, but your overall altitude has basically remained the same. In fact, you’ve lost around 40m. The following day is mostly up, but even then the height gain is 500m, which is within the recommended rates of height gain, but also by now you should be well acclimatised too.

So, over two days from Namche up to Pangboche your overall height gain is just 500m. After that, you’re basically losing height all the way.

We’ve done the planning bit. Now you need to do your bit too...

Insight Guides Exclusive Everest trip takes in the best of the Himalayan region. Review the full itinerary here

Relaxing at Lukla, Nepal. Photo: Trip providerRelaxing at Lukla, Nepal. Photo: Trip provider

How you can help yourself

Firstly, you should adopt a walking pace that is slower than your average pace and rest when you need to. Don’t let yourself feel out of breath. If you are, then stop, relax and take some deep breaths. Remember longer, deep breathing is best.

Just because you are acclimatising well, don’t spoil it. This is a common mistake. In your luxury trekking lodge there’ll be alcoholic drinks on sale. Resist any temptation to consume alcohol as it will have detrimental effects on your body’s natural acclimatisation. We’re not suggesting total abstinence: a glass of wine or a small bottle of beer is fine. But, as alcohol causes dehydration, that’s the last thing you want as remaining hydrated is very, very important. Smoking? A really, really bad idea at altitude.

Let’s look at what you should be doing in order to combat the effects of altitude and afford yourself maximum acclimatisation potential.

As we’ve just mentioned, you need to keep yourself hydrated. In other words, drink plenty of water. Most people will need to drink between 5 and 6 litres each day to achieve suitable hydration levels and you must adopt a responsible approach to achieve this target. Your body usually lets you know if it’s dehydrated (thirst, lack of energy etc), but even if it isn’t and you’re thinking “hey, I’m not feeling the effects of altitude at all” you must maintain the recommended fluid intake. Some of the less desirable effects of altitude are not always immediate.

We’ll repeat that it’s also essential that you walk at a slower pace than usual. It’s not a race and chances are you’re not wanting to run from one overnight halt to another. Again, you must discipline yourself to adopt a slower than usual pace. This is so that you are not over-exerting yourself. Feeling a bit breathless is to be expected at higher altitudes. Over-exertion does much the same. It’s your body’s way of telling you that it needs more oxygen. Although there is less oxygen in the air on this trek than at sea-level, there is still plenty of oxygen to breathe.

If you’re feeling breathless, don’t panic. Stop, rest, and breathe in and out slowly and deeply until your breathing returns to normal. Then set off walking again and keep to that slower pace.

Only one drug is currently known to have a useful role in preventing AMS (acute mountain sickness) and to be safe for this purpose: acetazolamide (Diamox). We recommend that you carry Diamox in your first aid kit. Diamox can be obtained from a medical professional on prescription and it is important that you first consult your own doctor so that you know there are no contradications with other medicines you may be taking and that you do not have an allergy to acetazolamide.

On trek, the decision whether or not and when you should take Diamox will rest solely with you. If you intend to take Diamox, you must familiarise yourself with the appropriate dosage and procedures prior to travel. Most doctors agree that taking Diamox before going to altitude is of little, if no benefit at all.

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Namche Bazaar, Nepal. Photo: Trip providerNamche Bazaar, Nepal. Photo: Trip provider

Your general overall health is important too

In my experience, altitude seems to find a way of exploiting existing medical conditions. If you or any of your party have an existing health condition you/they should consult your/their doctor for advice as to whether trekking/physical exertion at altitude could have an additional detrimental effect.

It’s perhaps also common sense to suggest that being in good health and with a good level of fitness helps to combat the effects of altitude. If your fitness levels are not good, while trekking you may over-exerting yourself by trying to keep up and, as we’ve discussed above, this is undesirable. 

It’s important that you familiarise yourself with the signs and symptoms of Acute Mountain Sickness (AMS) and that you report any illness to your guide straight away. It’s entirely possible that you may feel some of the symptoms of AMS at any time during your trek. Usually, these will be quite mild and if you are disciplining yourself to follow the recommended acclimatisation methods, these will usually reduce or disappear in 24-48 hours.

Before we continue, we should stress that AMS is not High Altitude Pulmonary Oedema (HAPE) or High Altitude Cerebral Oedema (HACE). These latter two conditions are very serious. The onset of AMS (if ignored) can quite possibly lead to HACE or HAPE, particularly if continuing to ascend to more extreme altitudes. But we should also stress that while not unknown, HAPE and HACE conditions are not common at the altitudes reached by the Exclusive Everest trek.

AMS is an early warning. Some of the symptoms of AMS include loss of appetite, nausea, sleeplessness, exhaustion and dizziness. Not necessarily all together. They can be mild or more severe. Either way, your body is telling you something important and you must listen and inform your guide. The guide has training in altitude related issues and will decide what is the safest course of action, depending upon the level of severity and circumstances. More often than not, symptoms are relatively mild and so ’taking it as easy as possible’ and maintaining the advised fluid intake minimises any disruption to the planned itinerary. But, you must always follow your guide's advice.

For more on altitude related matters we recommend you visit the NHS website:

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