What Happens To Your Body At High Altitude

In today’s post, we’re talking about the effect of altitude on the human body.

If you’re a high altitude trekker, this post is almost mandatory reading for you.

Especially if you plan to climb to any 15-16,000-ers like Roopkund and Rupin Pass.

First, let’s talk about what happens to the air at high altitude

You must know that anything above 8,000 ft from sea level is high altitude.

At this high altitude, the air pressure drops and there’s lesser oxygen available in the air.

Let me explain.

At a lower altitude, say, at sea level, there’s a certain amount of pressure in the air. At this pressure, air particles are pressed together, making the oxygen content in the air more concentrated. So one deep breath of air at sea level will give you a lot of oxygen.

However, as you climb higher, this pressure decreases. Air particles get scattered about. Consequently, even the oxygen in the air gets scattered. So the same deep breath of air at high altitude gives you lesser oxygen content.

This is what people often call “thin air” or “rarified air”.

It’s not lesser oxygen. It’s just lesser concentration of oxygen because of the lower pressure.

To give you an idea, the air pressure at sea level is 101.3 kPa (kilopascal). However, as you climb to around 16,000 ft (the altitude of Roopkund), the pressure drops dramatically to 54.8 kPa. Higher up, at around 29,028 ft (the altitude of Everest), it further drops to 30.8 kPa.

That’s less than one-third of the air pressure at sea level!

High-Altitude-classification-Indiahikes
This infographic gives you an idea of the oxygen level as altitude increases

That’s why you cannot suddenly climb from sea level to 29,500 ft in a day.  That would be like stepping out of a plane mid-air. (Most commercial planes fly at this altitude.) Your body will not cope with it.

It takes days to cope up an altitude like that — which is why most of our high altitude treks are around 8 days long with rest days in between.

This action of “coping up” by your body is called acclimatisation.

How does your body react to thin air?

Well, your body is used to a certain amount of oxygen at sea level.

When it suddenly gets lesser oxygen, it naturally tries to compensate by trying to take in more oxygen.

So your breathing becomes faster.

Next, your body recognises that there is lesser oxygen in your blood — so it compensates by increasing the quantity of oxygenated blood.

This means your heart starts pumping faster. Your pulse rate increases.

In your blood, red bed cells are the vehicles that carry oxygen. When your heart pumps faster, there are more red blood cells scurrying about.

But having too many red blood cells is not good for you. They can cause a sort of traffic jam in your body.

Think of the consistency of ketchup. That’s how your blood could become. It could also clot. Especially during times of inactivity.

Simply put, your blood becomes thicker.

Oxymeter-readings-Indiahikes
Oximeter readings are used on treks to determine the oxygen levels in your body. At high-altitude, your readings should not drop below 80.

Now, since both, your lungs and heart, are working harder than usual, your body tries getting rid of any excess baggage that it might be housing. It does this by getting rid of excess fluids — what it perceives as useless body weight.

This makes you urinate more often.

The scientific term for this is diuresis. A book I was reading by Stephen Bezruchka on this subject said you can lose nearly 2% of your body weight in water!

So at high altitude, it’s normal to wake up in the night to pee. If you’ve gone on a trek, it would explain all those midnight nature’s calls.

Another thing that may happen to your body is that you sleep less.

Often, your body forgets to breathe deep in your sleep. And your brain suddenly wakes you up to remind you to breathe! So if you don’t sleep too well at high altitude, it’s normal. It’s your body trying to acclimatise.

What you need to know about these changes in your body

The thing you need to know about all these changes in your body is that your body goes through these changes occur even while you’re resting.

This has nothing to do with trekking or mountaineering or any exercise.

Even if you’re simply lying down at high altitude, your body is spending a lot of energy, because it’s in overdrive.

Note that everything I have mentioned till now is about your body’s natural reaction to altitude gain. They aren’t abnormal changes. They are not “symptoms” of anything.

Most of our bodies go through these changes and adjust well to altitude. But sometimes, our body might respond more slowly, or may not respond at all.

That’s when we get altitude sickness.

If we understand the science behind it, it is not difficult to treat altitude sickness.

The biggest problem trekkers face is lack of knowledge.

Which is why I am writing this article.

I want you to start learning these things if you’re a high altitude trekker. If you already know these things, share your knowledge with others. The more you learn, the less dependent your life will be on others. For all you know, you could save someone else’s life!

In my following articles, I’ll dive deeper into how to prevent and treat altitude sickness.

For now, I highly recommend going through this page on our website to learn about anything altitude-related.

I hope you found this article helpful. Don’t hesitate to ask me if you have any questions. Also, if you think I’ve missed something out feel free to mention it in the comments section below.


What you should do now

1. If you want to read more articles on High-Altitude Research: Head over to this page, here

2. If you want to work with us: Head over to our careers page. We have lots of positions open. We also have lots of applications coming in. So the sooner you apply, the better.

3. If you ended up here by chance and were actually looking for treks to do: Then head over to our upcoming treks page. You’ll find all our Himalayan treks there.

4. If you want to see the 13 best treks of India: Then get our guide here.

You may also like

Swathi Chatrapathy

Swathi Chatrapathy

Swathi Chatrapathy is the Chief Editor at Indiahikes. She heads the content team and runs a video series called Trek With Swathi. Before joining Indiahikes, she worked as a reporter and sub-editor at Deccan Chronicle. She holds a Masters in Digital Journalism and continues to contribute to publications such as Deccan Herald. Trekking, to her, is a sport that liberates that mind like nothing else can. Through her work at Indiahikes, she hopes to let more people experience this sense of liberation, by spreading information about trekking and by instilling the right spirit of trekking in them. Read Swathi's other articles. Watch Swathi's video series here.

9 thoughts on “What Happens To Your Body At High Altitude

    1. Hi,
      We try to pace our treks in a way that the body gets time to acclimatise.
      If you don’t acclimatise and get AMS, and if your case is bad, then TL will make you descend to a lower campsite. But most treks have enough time to acclimatise. And on treks that climb too high, we have specific acclimatisation days.

  1. it is a very good article and all other articles regarding AMS, case studies are also very good and informative. I regularly follow IH website. What I feel is – all these documents should have a defined tab like “HOME’, ‘ UPCOMING TREKS, ” WHY CHOOSE US”. This may help a newbie or an experienced one to find out and read it easily.

  2. What exercises should I do daily, 1 month before my Roopkund Trek, so that my lungs are already ready for the trek and I can enjoy my trek?

    1. Hi Chinmay,
      Start going for a jog at least 5 days a week if you haven’t done so already. Target covering 5 km in 30-35 minutes about a week before starting your trek. In addition, also do some strengthening exercises such as stair climbing and squats.

  3. There have been studies on brains of high altitude trekkers (both amateur and professional , at both high and very high altitudes) that suggest that brain does not remain same after someone comes back from these treks.

    I found out about this from an article in Scientific American : https://www.scientificamerican.com/article/brain-cells-into-thin-air/

    And a few more such studies :
    1) https://www.ncbi.nlm.nih.gov/pubmed/16443427
    2) https://www.ncbi.nlm.nih.gov/pubmed/27633944
    3) https://www.ncbi.nlm.nih.gov/pubmed/26509635

    Please note that these studies are not talking about brain damage, but about morphological changes in brain and reduction in brain activity. E.g. someone’s IQ/brain capacity might drop or they may not be able to plan long term after returning from high altitude treks. These changes may not be immediately visible or may be occluded by the general fatigue which is there at end of treks. How might this be avoided or measured ?

Leave a Reply

Your email address will not be published. Required fields are marked *