The Basics of Altitude and How to Acclimatize


By: Tamara Kidd

      One of the biggest concerns in the alpine world, especially for those new to mountaineering, is altitude sickness. Doctors have yet to discover exactly what causes it, so most of what we know is based on trial and error from those who adventure into high altitude. The best ways to prepare for high elevation are to understand altitude acclimatization based on your health and training program, and to have the knowledge to deal with altitude sickness if you or one of your comrades experience such symptoms.

      Significant changes in atmospheric pressure, oxygen pressure, and humidity generally begin at about 8,000 ft. (2,438 m). At high altitude, the amount of hemoglobin in blood increases, which then increases the amount of oxygen that can be carried.  We can ultimately acclimatize by having just the right amount of hemoglobin to carry more oxygen without having so much that the blood becomes viscous. Too much hemoglobin makes it more challenging for the heart to pump its now sticky blood throughout the body resulting in acute mountain sickness. We know that the body can acclimatize to lower levels of oxygen in the atmosphere at a very safe rate of 1,000 ft per day, excluding those with certain heart conditions. Athletes have proven that they can go from sea level to over 14,000 ft. (4,267 m) in a 24-hour period or less with outstanding endurance, cardiovascular health and regular elevation training. Lastly, there is the “death zone” (anything above 26,247 ft./ 8,000 m)- named by alpinists for one’s inability to survive in it for more than a few days, and that’s with supplemental oxygen. You cannot sleep in the “death zone” without supplemental oxygen, but it is possible to move through this zone without it if properly acclimatized. This is where training and acclimatizing will only give you the ability to stay longer and move quicker; you can never fully acclimatize to such high altitude.

Most of us don’t have the luxury of living at or near high elevation mountains and running trails above 8,000 ft. However, while living at sea level, you can still adequately train and prepare for altitude. Ideally, get as much exposure training at higher altitudes as you can before your big summit attempt. This is not mandatory, but it will shorten the amount of time you need to acclimatize (more on this soon).  If you have any mountains or trails at elevation near you, take advantage of them every 3-5 days in the weeks leading up to your trip. This way you will already be training your heart with lower oxygen and increasing your red blood cell count before you begin the expedition. Climbing mountains is not a sprint; it’s an endurance race, so train your body, heart, and lungs for such a challenge. Training for speed and efficiency at lower heart rates translates best to mountaineering since it helps prevent altitude sickness by allowing you to move faster without overexerting yourself. This is one reason why ultra runners transfer to mountaineering so successfully.


Alpinists all have their preferred methods on acclimatizing, a lot of which is based on their regular training program. Regardless of personal preferences, after going high you need to go low. If you’re able to train above 8,000 ft. weekly, you can likely do a car-to-car ascent without any issues or prior acclimatizing (this is for 14k peaks and lower, the higher you go the more preparation and time you will need). Doing a car-to-car push is possible from sea level with no altitude training, but it’s a gamble.  Most of us don’t want to travel that far and take time off work just to take a chance on altitude sickness when it’s preventable. If you’re coming from sea level and are unable to expose yourself to altitude during training, your best bet is to have a base camp below 10,000 ft. to sleep before your ascent. Spend the first day going part of the way up (at least 1500 ft.) and going back down to camp, or wherever you’re sleeping, then going for the summit the next day. Training at elevation is the most important part, so whatever you can get in the day prior without tiring yourself out will benefit you most. Even if you are sleeping at elevation, it is important to travel higher than your camp before actually sleeping. There is much debate on whether or not sleeping at elevation is helpful. Some alpinists swear by it while others, like myself, despise it and would prefer to just train high then go down to a comfy, warm base camp with good food and better sleeping arrangements. Regardless of what you prefer, you cannot control your breathing during sleep which can cause a more rapid heart rate and have detrimental effects the following day. This is why it is so important to hike higher than you plan on sleeping that night. Another crucial part of acclimatizing is staying hydrated. This is not stressed enough even though dehydration will guarantee mild altitude sickness. Bring something to mix with water (example: 1-1 ratio of pedialyte and water) and make sure you are staying hydrated during the days leading up to the climb. Also, take in food or gels every 45 min or so. Keep in mind that it’s difficult to eat at altitude, so bring snacks that are appealing and easy to eat because you likely will not have much of an appetite.


There are three forms of altitude sickness: AMS, HAPE, AND HACE. Acute mountain sickness (AMS) is the mild form with similar symptoms as a hangover (headache, nausea, fatigue, vomiting, loss of appetite) and can range from slight discomfort to true agony. Getting AMS doesn’t mean you have to call it quits but be aware that it could develop into the more serious, and possibly fatal, HAPE or HACE. Stopping to rest for a few hours (sometimes 24-48 hours is necessary) may be enough to stop the symptoms. If not, you need to descend until you feel better. High Altitude Pulmonary Edema (HAPE) is a life-threatening fluid accumulation in the lungs. The primary symptom of HAPE is breathlessness while resting and can also cause a fever and frothy/pink saliva with ankle swelling, and blue lips/fingertips. If you have HAPE you need to descend to a lower altitude immediately or you will die. Ideally you need to descend until the symptoms are gone, which can range from a few hundred feet to over 1000 ft. (304 m). Supplemental oxygen and the medicine nifedipine may help alleviate symptoms but you still must descend. High Altitude Cerebral Edema (HACE) is fluid accumulation in the brain, essentially a severe form of AMS. HACE causes confusion, disorientation, clumsiness, hallucinations, and abnormal emotional or violent behavior. Extreme drowsiness, possible seizures, and loss of consciousness occur shortly before death. Supplemental oxygen and the steroid dexamethasone can help with symptoms and make the descent easier, but it is necessary to descend to the point where the person last woke up feeling well.

You or one of your climbing partners will likely experience AMS at some point during an expedition, which is why it is so important to know how to treat it and be physically capable of dealing with it. It’s nothing to be afraid of as long as you recognize the warning signs and push aside that normally helpful determination to get through pain and stopping your climb if you need to. It’s hard to tell everyone you need to rest when AMS hasn’t become bad enough to force you to stop and it’s equally as hard to tell a strong-willed comrade. You have a much higher chance of success by taking a rest day and going for the summit a day late than missing the opportunity entirely and needing your buddies to carry you down the mountain. A great time to stop and analyze how your group is feeling is right before entering any challenging sections in the climb that may be really hard to get down if you or someone else gets sick. What it all comes down to is preparation, knowing your limits, and adhering to altitude sickness. Happy climbing!