The 3 Stages of Altitude Acclimatization: How To Acclimate To Altitude Properly

In the summer of 2021, I moved from Winston-Salem, North Carolina, to Colorado Springs, Colorado. In doing so, I went from living and training at 1,000 feet of elevation to 6,500 feet of elevation.

Over the next few weeks and months, I spent much time researching and figuring out how to acclimate to altitude properly.

Whether you’re planning on visiting, racing, or moving to an area of high altitude, it’s best to know what to expect and how it will affect you and your running.

In this article, we will help equip you with the knowledge, tips, and tricks to proper altitude acclimatization so it will not get the best of you.

More specifically, we will examine:

  • How Altitude Affects Your Physiology
  • Altitude Acclimatization: How Long Does It Take To Acclimate To Altitude?
  • What Are The 3 Stages Of Acclimatization To Altitude?


Let’s jump in!

A sign in the snowy mountains that says: 4680 m.

How altitude affects your physiology

Most of us have a general understanding of why it is tough to travel and exercise at high altitudes. The common answer is there is less oxygen in the air as altitude increases. This isn’t technically correct.

The amount of oxygen in the air stays constant at 21% regardless of if you are at sea level or if you are at the top of Everest. What changes is the air pressure, which means you are able to breathe in less air as you increase in altitude.

Here is a great TedTalk explaining the process.

So how does altitude affect your physiology?

Your body responds to altitude with some immediate changes and then more drawn-out changes. Let’s look at each one in detail:

A person running at high altitude.

Immediate changes

The first change your body makes is that it begins to hyperventilate. Your body is receiving less oxygen, so its response is to make you breathe faster to bring more in.

Your body will also increase your heart rate and blood pressure.

The increased heart rate will speed up the rate at which blood moves through your body, allowing it to get oxygen to your tissue. Increased blood pressure also helps speed blood through the body.

Your body will increase its metabolism by producing more epinephrine and adrenaline.

These two hormones will also help with the increased blood pressure and heart rate, which we discussed above.

Lastly, your body will also experience fluid loss.

While this can be a negative, leading to dehydration, it will also decrease the plasma volume. We will discuss why this is a positive in the next section.

People hiking in the snow.

Long term changes

If you are familiar with professional runners or other endurance athletes, you may be aware that they do stints at high-altitude camps during their training. The reason for this is so they can reap the benefits of the long-term changes that we are about to discuss.

We mention fluid loss above. This leads to a decrease in plasma volume. Why is this a benefit?

A lower blood plasma volume leads to a higher concentration of red blood cells, or hematocrit, and a higher concentration of hemoglobin. The more these increase, the more oxygen can get into your tissues.

In addition to a higher concentration of red blood cells, your body will also begin to produce more red blood cells. This actually increases the production of a substance you might have heard of in a negative connotation: EPO.

Our bodies naturally produce this performance-enhancing drug, and we can increase production at high altitudes. Don’t worry; your metrics will be well within the acceptable range should you have to take a drug test.

Your body will also increase capillaries. Capillaries are tiny blood vessels that oxygen travels through to get blood to your tissues. More capillaries mean more blood, which means more oxygen.

An interesting aside, distance running and endurance sports are one of the few things that can cause your body to increase the production of capillaries.

A person on the top of a mountain, at high altitude.

Altitude Acclimatization: How Long Does It Take To Acclimate To Altitude?

So, how long to acclimate to altitude?

Most people are able to travel up to 8,000 feet without the need to acclimate. If you are traveling higher, the Center for Wilderness Safety states it typically takes 1-3 days at an altitude to acclimate. After this, your body will begin to feel normal at that altitude.

While this might be the case for walking or hiking, I’ve found things to be slightly different for running.

When I lived at sea level and traveled to Colorado Springs (6,000 feet), I noticed a decrease in my running performance. Runs at my easy pace felt pretty normal, just a slightly elevated heart rate and breathing rate.

As I increased my pace, I noticed that I had to work much harder and was not able to run at the same pace as I had at sea level.

When I moved to Colorado, It was probably 6-8 weeks before I felt like I was back at the sea level benchmarks that I was used to.

Altitude acclimatization can be different for everyone. The best bet is to take it easy for a few days and gradually see how your body handles the elevation.

A person looking out at snow-capped mountains.

What Are The 3 Stages Of Acclimatization To Altitude?

Altitude acclimatization is the process of gradually introducing your body to higher altitudes so that it can adapt. This is typically only necessary if the individual travels to an altitude of around 10,000 feet (3,000 meters) or higher.

To effectively acclimatize to higher altitude, you can follow an altitude acclimatization 3-step process: preparation, ascent, and descent.

#1: Preparation

The preparation stage of altitude acclimatization is all about preparing your body for higher altitude by gradually introducing it to higher altitudes.

For instance, if you were getting ready to run the Leadville 100, which starts at 10,000 feet of elevation and has a high point of 12,500 feet, you might fly into Denver, CO, and stay a few days.

Denver, the Mile High City, sits at an elevation of 5,280 feet. Staying a day or two at this elevation will allow you to acclimate before heading to Leadville, CO, which sits at 10,000 feet of elevation.

It’s also important to take it easy the first few days at altitude as your body adjusts. Pushing too hard early on could mean you spend the rest of your time trying to recover. For locations even higher in altitude, like a Himalayan peak, it is even more important to spend time in the preparation stage.

Base Camp at Mt. Everest sits at 20,000 feet. Most climbers who climb the peak will fly into Kathmandu, which sits at 4,500 ft. They will then spend several days/weeks hiking to base camp to allow their body to acclimate to the high altitude. Once there, they spend several days doing short hikes and acclimating before starting up the mountain.

A person hiking Everest.

#2: Ascent

When making the ascent, it’s best to keep in mind that you typically don’t want to sleep higher than 1,600 feet per day. In addition to this, for every 3,300 feet you climb, you will want to spend an extra day at that elevation to acclimate.

On Everest, climbers will typically spend time climbing up to camps 1, 2, and 3, staying a day or two, then coming back down. This process allows them to adhere to these tenants and acclimate to the high altitude as they try to prepare to make a push for the summit.

#3: Descent

You’ve made it to the summit. The hard work is over, and now it’s just time to come back down. While the descent may seem like the easiest part, your body is still working hard at a high altitude. You want to make sure you are not overdoing it during this period.

If you are in Colorado bagging a 14er (the nickname for a peak over 14,000 feet), take a few minutes at the summit to rest and enjoy the view before starting back down.

I ran two marathons last summer, Leadville Marathon and the Pikes Peak Marathon. Both included a tough climb that brought me over 13,000 feet to their summits (13k for Mosquito Pass at Leadville and 14k for Pikes Peak at the Pikes Peak Marathon).

Both of these races had an aid station at the top with food and hydration for runners. I made sure to take my time to get calories in and let my breathing and heart rate get controlled before starting the descent back down.

If you are traveling to altitudes of higher than 10,000 feet, you may want to watch for symptoms of AMS, HAPE, and HACE.

A person looking out at a mountain view.


AMS is acute mountain sickness. In its mildest form, AMS can feel like a hangover. Symptoms may include a headache, dizziness, muscle aches, and nausea.

Symptoms typically begin 24-48 hours after arriving at a high altitude and go away as you acclimate. While you can generally mitigate the onset of AMS by taking your time when increasing your altitude and taking it easy the first few days you are at altitude, it can affect anyone of any fitness level.


HAPE stands for high altitude pulmonary edema. This is a buildup of fluid around the lungs and is very dangerous, if not life-threatening. It is the most common cause of death from altitude sickness.

Symptoms of HAPE include shortness of breath at rest, cough, decreased exercise performance, and chest congestion. If someone is suspected of suffering from HAPE, it is best to get them lower altitude as quickly as possible.

A person looking out at a mountain view.


HACE is high-altitude cerebral edema. This is a buildup of fluid around the brain and is the most severe form of altitude sickness. It is life-threatening, and the individual should seek medical attention immediately.

Symptoms include loss of consciousness, fever, ataxia, and rapid heartbeat. If someone is thought to be suffering from HACE, they should be brought to a lower altitude and provided supplemental oxygen.

While altitude sickness can affect anyone, regardless of fitness level, it can be mitigated by gradually increasing altitude and taking time to properly acclimate.

With proper planning, you can properly acclimate to high altitude so that you can enjoy your time in the mountains.

For a list of some of the best places to train at altitude, check out our guide: The 5 Best Altitude Training Destinations in the World.

A person hiking at a high altitude.
Photo of author
Adam Rabo has been running since junior high. He has coached high school and college distance runners. Adam recently completed the UTMB Canyons 100k, making the cutoff for the Western States 100 and UTMB. You can generally find him on the rodes or trails in Colorado Springs, training for upcoming marathons and ultramarathons.

1 thought on “The 3 Stages of Altitude Acclimatization: How To Acclimate To Altitude Properly”

  1. Very well written. Before finding your website and this story I ran across several discussions of how to acclimate at 8 or 9,000 ft in ski areas. 2 to 3 days seem to be enough. Well, we spent 27 years at 8900 ft. The last few years, and we were by then well into our ’70s, we would head for Phoenix for about 5 months. On the return home we might have very light headaches for a couple of days, and I was not back up to Ranch work for about 2 weeks. By the way, I first crossed Wolf Creek Pass from the Alma side in 1971. Been doing it occasionally until we left in 2016. Something about that feeling I get at the top by the priest’s Monument really puts me in touch with a greater power. And I’m far from a religious guy.


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