The physiological effects of high altitude, why elevation is measured in reference to sea level, and techniques to help manage working out at high altitudes
The peak of Mt. Everest is the tallest point on Earth. It stands at an altitude of 29,032 feet above sea level. Thus, it has become the obsession of many mountaineers to climb this towering behemoth. For them, climbing Everest is an ultimate physical and mental challenge to overcome.
The climbing obsession is not limited to just Everest. There are 14 peaks in the world that stand over 8000 meters above sea level. Even “relatively smaller” mountains present worthy challenges. Mt. Rainier in Washington stands at 14,411 feet above sea level and is famous for its mountaineering.
Even if you don’t climb mountains, you probably have firsthand experience with the physical effects of high altitude. If you’ve ever done any type of cardiovascular activity in cities at higher elevations than where you live, you’ve likely noticed the physiological effects. Increased breathing, slower pace or output, maybe some lightheadedness or dizziness. Essentially, your workout was probably more difficult.
So why does altitude have these physiological effects? Scientifically, what is it about high elevations that causes these effects?
Why is elevation commonly measured in reference to sea level? What is so important about your elevation above the sea as it relates to the physiological effects you may be experiencing?
What does sea level even mean? How is that measured or defined? And most importantly, is there a better, or more accurate, way of measuring elevation? By more accurate I mean a metric that more highly correlates with the physiological effects associated with being at higher altitudes.
Finally, are there any methods or techniques (other than medications and acclimatization) that mountaineers and non-mountaineers alike can use to help overcome the physiological challenges of high-altitude excursions?
The Physical Challenges of High Elevation
So we already know that higher elevations present physical challenges. Manifestations of this include but are not limited to: shortness of breath, reduction of pace or output, dizziness or lightheadedness, lack of appetite, nausea, confusion.
Depending on how long one is at higher altitudes for, how high they are, and how hard they go, things can get pretty serious. Acute Mountain Sickness (AMS) can lead to life-threatening conditions of high-altitude pulmonary edema (HAPE) or high-altitude cerebral edema (HACE).
All of these ailments and difficulties boil down to one primary factor: lack of oxygen. The higher the elevation, the harder it is to get oxygen into your body, brain, bloodstream, etc. Here’s where the most common myth regarding high altitude becomes prevalent. Most people believe that there is less oxygen in the air at higher altitudes. This is false.
Air has more or less the same percentage of oxygen in it at all altitudes: 21%. The reason it becomes harder to acquire oxygen at higher elevations is actually something called barometric pressure.
Barometric pressure is a fancy word for the pressure in the air at a given point. This is what is relevant for us, because it is what leads to the “lack of oxygen” that causes all of the aforementioned difficulties. The lower the barometric pressure of the air, the more difficult living and exercising become.
Why does low air pressure cause a lack of available oxygen? With a lower air pressure, less oxygen enters your body as you breathe. The way breathing works is you essentially expand your lungs. This creates a lower pressure of air inside your lungs as compared to the pressure of the air around you.
With this pressure differential, air rushes in through your mouth and nose to your lungs to try to equalize the pressure differential. Nature always tries to equalize pressure differentials (side note: this is actually what causes wind. Wind is just air moving to equalize pressure differences in the air).
So, the higher the pressure of the air around you, the higher the pressure differential will be between it and your lungs. The lower the pressure of the air around you, the lower this pressure differential.
The pressure differential is what dictates how quickly and readily the air and oxygen will flow into your lungs as you breathe. All other factors being equal, a higher pressure differential will lead to more oxygen and air entering your system per breath.
This is why a lower air pressure, or barometric pressure, leads to a lack of oxygen. With a lower barometric pressure, the pressure differential between the outside air and your lungs is less. So less air and oxygen enters your system per breath.
High Altitude Air
OK, so we know that working out at high altitude is hard because it’s harder to breathe in as much oxygen. And the reason it’s harder to breathe in oxygen is not because there is less oxygen in the air. It is because there is less pressure in the air. Queue the next question: why is there less pressure in the air at higher altitudes?
This actually gets pretty complicated, as there are a number of different factors at play. And to be honest, not all of the effects are fully understood, even by field experts.
It turns out that the primary determining factor of barometric air pressure is the weight of the air molecules above a given point that are pressing down on that point. It’s best to explain this with an analogy.
If you’ve ever dove down in the ocean or a pool more than a few feet, you’ve likely noticed that your ears may start to hurt, unless you pop them. The reason this occurs is because there is a lot more pressure the deeper in the water you go.
At the bottom of the ocean, the pressure is so great that only the most hardcore of organisms can survive. If you and I went to the bottom of the ocean, our entire bodies would collapse and pretzel like what happens to an empty plastic water bottle if you squish it or suck all the air out of it.
Conversely, if you took those organisms that are adapted to survive near the bottom of the ocean and brought them up to the surface, they would immediately explode, since their bodies are not used to the lower pressure closer to the surface.
The reason the pressure increases the deeper you go has to do with the weight of the water molecules on top of you. Suppose that right now, as you read this, I took a 1 ft. by 1 ft. hollow column that was really tall and placed it on top of your head.
Now imagine I gradually started filling that column up with water. At first, you wouldn’t notice much. But the more water I poured, the higher the height of the water in the column would rise, and the more weight would be pressing down directly on top of your head.
Water is actually very heavy. 1 liter of water (standard water bottle size) weighs about 2.2 lbs. Eventually, the height of the water in the column would get so high that you would not be able to bear the weight of the water pressing down on you anymore.
This little thought experiment is basically analogous to what happens to you when you dive down deep into an ocean or pool. The deeper you go, the higher the “column” of water pressing down on top of you is, which means there is more weight pressing down on you and surrounding you. This leads to increased pressure.
Bring it Back to Air
It turns out that the water analogy is brilliantly similar to why air pressure decreases at higher altitudes. We essentially are living at the bottom of an ocean of element air. Our atmosphere is the air ocean.
The lower you are, the “deeper” you are in the “air ocean”, so the greater the air pressure. The higher you go, the less air molecules are pressing down on top of you, so the lower the air pressure.
To complete the analogy, the outer edges of our atmosphere would be the “surface” of the “air ocean”. So the closer you are to the edge of our atmosphere, the less the air pressure.
OK, so high altitudes are hard to work out and exist in. They are harder than lower altitudes because it’s harder to breathe in as much oxygen.
It’s harder to breathe in as much oxygen because the air pressure is less at higher elevations. With a lower air pressure, less of a pressure differential exists between the air and your lungs, so each breath takes in less air and oxygen.
The air pressure is less at higher elevations because we are living in an ocean of element air. The closer you get to the surface of this ocean (the closer you get to the edge of our atmosphere), the less the weight of the air molecules pressing down on you. Which means less air pressure.
Got it? Good. This brings us to the next important question to ponder.
Elevation Above Sea Level
All elevation in our society is measured in reference to sea level. You could be at sea level. You could be in Denver at one mile above sea level. Or you could be on top of Mt Everest, at over 29,000 feet above sea level.
Why is sea level the reference frame by which all elevation is measured? Is it the best proxy for barometric pressure, since as we determined, barometric pressure is what has the most important effect on human physiology?
What does sea level even mean? How is it measured or determined?
Let’s start with the latter two questions and go from there.
How is Sea Level Measured and Defined
On the surface, this question has an obvious answer. Sea level is simply the level of the water in the ocean. But there are surprising intricacies and complexities to the answer of this question.
The first and most obvious question: how do you measure sea level in areas where the ocean does not exist, like areas surrounding most mountain peaks? Another question: does the “level” of the sea change over time? How does this affect measured elevations?
Sea level is constantly changing. Even ignoring the effects of climate change, other factors like tides, waves, and precipitation all change the sea level. Even astronomical and natural effects like the moon, sun, wind, and the gravitational pull of other planets all impact the level of the sea.
So essentially, sea level is constantly changing. For this reason, it is measured by averaging the height of the sea throughout all ocean stages over an extended period of time. It is, at best, a rough approximation.
For areas where the sea does not physically exist (continents, mountains, etc.), sea level is estimated. The meaning of this estimate is essentially the answer to this question. If you were to dig a large canal from a given point on land to the ocean, what would the height of the water be at that point?
However, it is hard to estimate this perfectly accurately. It is not directly observable. Additionally, there are many confounding factors like planets and stars. Even mountains and other terrain features can have a local impact on sea level! Sea level is estimated now using satellite images and sophisticated measuring techniques, which are not perfect.
In summary, it is hard to perfectly measure sea level. It is at best an approximation and estimation of a constantly changing phenomenon.
Why is Elevation Measured From Sea Level
If sea level is hard to estimate accurately, why do we use it as our baseline reference for measuring elevations?
Sea level was chosen historically because water is relatively uniform. In a perfect world, if you removed all factors like the Sun, planets, moon, etc., water would settle to a uniform level on the globe. For this reason, sea level is the best approximation we have to define the level of the “surface of the Earth”.
This brings up the question though. Could we use a different metric for baseline elevation that’s more objectively measured and potentially more indicative of the actual physiological difficulties of high altitude?
Baseline Reference of Elevation
We ideally want a baseline reference of elevation that provides an accurate proxy for the physiological effects one would experience from working out or living at a given elevation above the baseline.
And remember that air pressure is the relevant determining factor for these physiological effects. So we want a reference of elevation that provides an accurate baseline of air pressure.
Remember that air pressure is determined by the amount of air “on top of” a given point. For this reason, the most accurate baseline reference for elevation would be distance from the edge of the atmosphere.
This would be analogous to how your depth below the surface of the ocean is very highly correlated with pressure at that point. The surface of the ocean becomes the “reference” point, and all distances are measured from that. One who is 20 feet below the ocean surface experiences higher pressures than one 10 feet below the ocean surface.
Unfortunately, distance below the edge of the atmosphere is nearly impossible to measure directly. So when choosing a baseline reference for elevation, we want one that is closely correlated with distance below the edge of the atmosphere.
What about the idea of measuring elevation of a point by its distance from the center of mass of the Earth? This would be more accurately measurable than sea level.
Distance From Center of Earth as Elevation Metric
Which method more closely approximates distance from the edge of the atmosphere?
Distance from the center of mass of the Earth would give us an accurate measure of the strength of gravitational pull at a given point. However, it is a poor estimator for air pressure.
It turns out that the atmosphere is actually deeper around the equator than the poles. The edge of the troposphere is about 17 km above the Earth’s surface near the equator, compared to about 4 km above the Earth’s surface near the poles. For this reason, the closer you are to the equator, the higher the air pressure!
This means that if you take two points equidistant from the center of the Earth, one near the equator and one near a pole, the one near the equator would have a much higher air pressure.
The peak of Mt. Chimborazo in Ecuador is actually farther from the center of the Earth than the peak of Mt. Everest! Yet, because Everest is closer to the poles and Chimborazo is closer to the equator, Chimborazo still has way higher barometric pressure than Everest. Pretty wild!
So for this reason, distance from the center of the Earth is a poor estimator for barometric pressure. But is sea level any better? The answer is yes… but it’s still not great.
Distance Above Sea Level as Elevation Metric
For points at similar latitudes, elevation above sea level is a pretty good baseline reference for atmospheric pressure. This is because the edge of the troposphere is at a similar height above the Earth/sea level for points at comparable latitudes. So, the amount of “atmosphere” that is above you at sea level is very comparable between two points of comparable latitudes.
And that amount of atmosphere above you decreases relatively uniformly as you ascend in elevation above sea level. Thus, being 10000 ft above sea level would feel pretty comparable in two different locations with similar latitudes.
However, elevation above sea level starts to fail as a useful comparison tool if the points you are comparing are at different latitudes. Again, this is because there is much more atmosphere above the surface of the Earth near the equator than the poles. 10,000 ft above sea level at the North Pole will have a lot less air pressure than 10,000 ft above sea level in Ecuador.
Another confounding factor is that temperature actually impacts atmospheric pressure, somewhat significantly. Warmer air has higher pressure, colder air has less pressure.
Even the same location at the same elevation above sea level will have vastly different barometric pressure depending on the temperature. The peak of Mt. Everest will have significantly more barometric pressure in the summer than the winter! Sometimes, K2 is “higher” than Mt Everest, in terms of barometric pressure!
Elevation above sea level is imprecise, arbitrary, and hard to measure. However, it is our best known proxy for the amount of atmosphere above a given point, which determines barometric pressure. And barometric pressure is what determines how hard it is to work out or exist at a given elevation.
Barometric pressure can be measured directly with a barometer. However, it changes frequently, even at the same point in space, with small fluctuations in temperature and other factors.
Thus, for better or worse, elevation above sea level has become the proxy for barometric pressure. Barometric pressure impacts oxygen availability. And oxygen availability determines the relative difficulty humans have working out or existing. And this relative difficulty has become the yardstick people measure and compare themselves by.
People weigh the challenges of summiting mountains by how high the peak lies above sea level, rather than the highest barometric pressure recorded during the push, which would be more relevant.
But alas, that’s where we’ve arrived at as a society. And frankly, there are bigger societal problems to solve than the inaccuracies of using elevation above sea level as a mountaineering metric.
Techniques and Methods for Dealing With High Altitude
I have never been particularly good at dealing with high altitude. I consider myself to be a fairly fit individual. I do a lot of backcountry skiing and mountaineering. However, it seems that whenever I get 9000 feet or above, I really struggle.
People are generally split into 3 categories when it comes to dealing with high elevation:
- Those who excel
- Those who experience difficulties but can work through them
- Those who really struggle
I consider myself to be squarely in category 3.
Part of my motivation for doing the research behind this post was to understand more about my struggles at altitude to see if there was anything I could do about it. Unfortunately, there are a lot of genetic factors that largely determine how well an individual does at altitude.
There are also nurture factors. Where you were born and where you live impact your ability to cope with altitude. If you were born and live in Nepal, you will generally do better with higher altitudes than if you were born and live in Seattle (close to sea level).
Acclimatization and medications that help prevent hypoxia and acute mountain sickness are the most common tools people employ to help with altitude. And for extreme high-peak summits, supplemental oxygen is common.
However, in my research for this post, I came across an alternative technique to help with the difficulties of high altitude. It appealed to me as a simple, easy-to-test technique that could work. Admittedly, I have not had a chance to try it yet. But it sounds promising.
Deep Breathing and Pressure Breathing
I’d never thought about breathing technique being a tool one could use, practice, and employ on the mountain to help combat the effects of lower oxygen availability. So I was surprised and intrigued to learn about two breathing-related techniques, deep breathing and pressure breathing, that supposedly help to do just that.
It is common to shorten your breathing pattern when you’re at high altitude exerting yourself. However, it turns out this is actually not optimal. It helps to consciously focus on your breathing to make it deeper. Consciously try to inhale more oxygen by breathing more fully.
At first, this breathing should be slow, but it will naturally need to speed up as intensity increases. Even when this happens, it is important that the breaths are still deep and concentrated.
Breathe with focus, and breathe more than you think you need to.
On the exhale of your breaths, purse your lips and exhale forcefully. The logic behind this is that it helps to more rapidly reduce carbon dioxide levels in your blood and muscle cells by forcing more carbon dioxide into the exhale.
This is important for several reasons. Carbon dioxide increases the acidity of your muscle cells, and eventually can cause them to need to shut down (aka rest). Additionally, clearing out the carbon dioxide can help to reduce the pressure in your lungs and body. This increases the pressure differential between your lungs and the outside air, which allows you to intake more oxygen.
Thanks for taking the time to read about elevation and altitude. I hope you learned something. Are there other aspects about elevation, altitude, and the way the body adapts that you’d like me to analyze? Do you have any tips or tricks you use to perform better at altitude?
Let me know in the comments below!