Physiological Impacts

The body undergoes several physiological changes to cope with the decreased oxygen availability and other environmental stressors. These adaptations occur over a period of days to weeks and help improve oxygen uptake and delivery to your tissues. Here are some of the key physiological changes that take place during acclimatization:

• Increased Breathing and Depth: One of the primary responses to high altitude is an increase in breathing rate and depth (ventilation). This helps to compensate for the reduced oxygen pressure in the air, allowing for greater oxygen intake and delivery to the bloodstream.
• Increased Heart Rate: Acclimatization will impact both resting and active heart rates to maintain cardiac output and blood pressure in response to the lower oxygen levels at altitude. 
• Increased Urination: Acclimatization may involve changes in fluid balance, including increased urine output and changes in electrolyte levels, to help regulate blood volume and blood pressure at high altitudes.
• Blood Changes: To enhance oxygen transport, the body increases the production of red blood cells in response to hypoxia. This occurs primarily in the bone marrow, stimulated by the release of erythropoietin (EPO) from the kidneys. Higher red blood cell counts improve the blood’s oxygen-carrying capacity.
• Muscle Changes: With acclimatization, muscles may become more efficient at utilizing available oxygen. This adaptation helps to maintain physical performance at high altitudes despite reduced oxygen availability.

These physiological adaptations allow the body to function more effectively in low-oxygen environments and mitigate the negative effects of altitude on physical performance and well-being. Your body is doing some pretty cool things while you acclimate to allow you to reach the summit in good style. You will hear us press this issue over and over again: it’s incredibly important to remember that individual responses to altitude vary, and not everyone acclimatizes at the same rate or to the same extent. Some of the best climbers in the world need to allow more time for their bodies to adapt to altitude.

Importance of Acclimatization

Acclimatized climbers generally experience less discomfort and distress at high altitudes, allowing them to enjoy mountaineering more fully, recover more quickly, stave off altitude sickness, and increase overall physical performance. Here is a quick look at why it’s so important to acclimatize properly. 

• Improved Physical Performance: Acclimatization allows the body to adapt to the reduced oxygen availability, which enhances physical performance. Climbers who acclimatize properly are better able to maintain strength, endurance, and mental clarity, which are essential for safe and successful ascents.
• Increased Oxygen Uptake: With acclimatization, the body increases its production of red blood cells and improves oxygen uptake efficiency by the muscles and tissues. This adaptation helps maintain adequate oxygen delivery to vital organs, reducing the risk of hypoxia and its associated symptoms.
• Better Temperature Regulation: High altitudes often come with extreme temperature variations, including intense sunlight during the day and freezing temperatures at night. Acclimatization allows the body to better regulate its temperature, reducing the risk of hypothermia or heat-related illnesses.
• Reduced Risk of Exhaustion and Injury: Climbers who are properly acclimatized are less likely to experience fatigue, exhaustion, or impaired judgment, reducing the risk of accidents and injuries on the mountain.

Prevention of Altitude Sickness: Acclimatization helps the body cope with the lower oxygen levels present at high altitudes. Without proper acclimatization, climbers are at risk of developing acute mountain sickness (AMS), which can range from mild symptoms like headaches and nausea to more severe conditions like high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE).

CTSS Acclimatization Schedules

One of the most common questions we’re asked about acclimatization and high-altitude environments is how to predict what your body will do on your next climb. It’s imperative that anyone going into the mountains understands that individual responses to altitude vary, and not everyone acclimatizes at the same rate or to the same extent. Plus, your response each time will be different because of different environmental and physical factors, including how much water you’ve consumed, where you are in the world, and the overall weather conditions, all of which affect your ability to acclimatize on a particular expedition. Just because you acclimatized well on Kilimanjaro doesn’t mean your body will do the same on Aconcagua. Remember, some of the best climbers in the world need to allow more time for their bodies to adapt to altitude, and it’s okay if you’re in the same boat. 

To acclimatize well, the body needs to be exposed gradually to new high points and then given time to adjust. Think of it like going to the gym, where we deliberately put stress on our muscles before letting them recover. When we return to the gym, we are stronger. Altitude and acclimatization work similarly, and this practice is often called climbing high and sleeping low.

On a well-planned acclimatization schedule, each jump in elevation is staggered by a rest/acclimatization day or a carry day. Our goal on a rest/acclimatization day is to reach a new high point (climbing high) in elevation before dropping back down to sleep low. This puts manageable stress on the body and prompts it to adjust to a new environment. Once we have exposed our body to that new high point, retreated, and rested, we can move up to a new elevation, and the process repeats.

CTSS Sample Acclimatization Schedules

For example, during our Everest Base Camp Trek, we generally stay two nights in each village and take a short acclimatization hike above the village on the rest/acclimatization day to reach a new high point. Despite the trail only being 40 miles, it takes us 11 days to reach Everest Base Camp because of the need to acclimatize along the way. 

Another example is from our Aconcagua expedition, where we follow the same principle of climbing high and sleeping low, but it looks a little different as the acclimatization days double as carry days. When we climb Aconcagua, we take all the gear we need for the entire expedition with us, all the way up and down the peak. We spend two nights at most camps, using the first day as a carry day to bring a load of gear to the next camp and cache it before returning for a second night at our current camp. This carry day is also your acclimatization day since you will be climbing high and sleeping low. The second day is a move day when we climb back up to the gear we cached the day before and establish camp. Rest days are scattered throughout this itinerary to ensure climbers are prepared for their summit push. 

On Mount Everest, a proper acclimatization schedule can take 6-8 weeks. From the time climbers arrive in Kathmandu, trek to Everest Base Camp, and undertake a series of rotations to subsequently higher points on the mountain, the body is making impressive physiological changes to allow the climber to ascend to 8,848 meters (29,032 feet). Acclimatization is exactly why it takes two months to climb Everest. Once a climber is fully acclimatized, the final rotation only takes 5-7 days from Everest Base Camp to the summit and back.

Pre-Acclimatization Strategies Before an Expedition

• Fitness Training: Your climb and acclimatization begins long before you step foot on the mountain. By incorporating proper training into your daily routine for at least six months before your departure date, you will help set yourself up for success as you acclimatize during your expedition. Remember, training doesn’t stop with just your fitness, and it’s crucial to be in top mental condition. 

• Hypoxic Training: Hypoxic training involves exposing the body to reduced oxygen levels. This can be achieved through training in natural high-altitude environments to stimulate the physiological adaptations you will experience during your trip. Training in high-altitude environments will ultimately improve your performance and reduce susceptibility to altitude sickness during your expedition. 

• Use of Hypoxico Tents and Chambers: If you are unable to travel to natural high-altitude environments, you can mimic the physiological adaptations experienced at altitude using Hypoxico Training Systems. These systems and devices allow mountaineers to acclimatize gradually at home in a controlled environment by reducing oxygen levels while sleeping or exercising. 

Acclimatization Strategies During  an Expedition

We employ a number of acclimatization strategies during our expeditions, which involve increasing altitude exposure in a deliberately unhurried manner, allowing the body time to adapt to the decreased oxygen levels, and taking rest days as a built-in feature of our itineraries. Here’s an overview of the acclimatization techniques we employ on all of our expeditions. 

• Importance of Gradual Altitude Gain: A metered approach to altitude gain is critical for acclimatization because it allows the body to slowly adjust to decreasing oxygen levels. Climbing too quickly increases the risk of altitude sickness, as the body doesn’t have enough time to adapt.

• Slow Ascent Rates and Rest Days: Slow ascent rates and rest days are essential components of gradual ascent acclimatization. You’ve heard us say climb high, sleep low? These periods of venturing high and then sleeping lower allow our bodies to rest and make the critical adaptations for altitude. Rest days also provide an opportunity to monitor for symptoms of altitude sickness and adjust ascent plans accordingly.

• Hydration and Nutrition: On any expedition, hydration and nutrition play an integral role in how you feel in the mountains. On the flip side, due to long travel time, busy trip itineraries, and an all too often lack of appetite, it can also be hard to remember to adequately eat and drink. You must ensure that you don’t get behind on your food and fluid intake. To make things easier, we recommend training to eat and drink in the mountains along with your regular fitness training.

• Pharmacological Interventions: Medications can be used for altitude sickness prevention or treatment. Acetazolamide (Diamox) is a commonly prescribed medication that helps stimulate breathing and reduce the risk of altitude sickness. Other medications, such as dexamethasone or nifedipine, may be used for severe cases of altitude sickness. However, pharmacological interventions should be used judiciously, and climbers should be aware of potential side effects and interactions with other medications.

Hypoxico Altitude Training Systems

If you’re looking for a quicker timeline on the mountain, a hypoxic tent can shorten your expedition by facilitating acclimatization to high altitudes before your actual climb. Many climbers don’t have unlimited time off to pursue their mountain dreams and have busy lives with family and work, so utilizing a pre-acclimatization strategy that involves the use of a Hypoxico tent can help to shorten time away from work, family, and friends. Here’s how you can incorporate pre-acclimatization by using a hypoxic tent to expedite the acclimatization process.

• Pre-Trip Preparation: Before the mountaineering trip, set up the hypoxic tent in a comfortable and convenient location, over your bed or a guest bed if your pets or partner usually sleep with you and don’t want to also acclimatize. Ensure that the tent is properly installed and ventilated according to manufacturer instructions.

• Gradual Exposure: Begin using the hypoxic tent 6 – 8 weeks before your expedition. Start with a lower simulated altitude, typically equivalent to around 1,500 meters (5,000 feet) above sea level, and gradually increase the altitude over time. For every night that you sleep well, ascend 150 meters (500 feet). If you do not sleep well, remain at that altitude until you do, then ascend in altitude. Ascend until you have hit the altitude you are trying to acclimatize to. 

• Consistent Use: Sleep in the hypoxic tent each night to expose your body to the reduced oxygen levels. Consistent nightly exposure helps stimulate physiological adaptations similar to those experienced at high altitudes, such as increased red blood cell production and improved oxygen utilization.

• Training Sessions: In addition to sleeping in the hypoxic tent, incorporate training sessions or workouts while breathing the reduced oxygen air. This can help enhance cardiovascular fitness and endurance, further preparing you for the physical demands of the mountaineering trip.

• Monitoring: Throughout the acclimatization process, monitor your response to the hypoxic exposure and adjust the altitude settings as needed. Pay attention to any symptoms of altitude sickness or discomfort and consult with a healthcare professional if necessary.

• Supplemental Training: While using the hypoxic tent, continue to engage in supplemental altitude training activities, such as hiking, climbing, or aerobic exercises, to further enhance acclimatization and physical conditioning.

By using a Hypoxico tent to simulate altitude exposure before the mountaineering trip, you can expedite the acclimatization process and reduce the time on an expedition by 30-50%. As always, if you are using a Hypoxico system, it’s essential to supplement your Hypoxico tent usage with other aspects of mountaineering preparation, including physical training, proper gear selection, and knowledge of altitude-related risks and safety protocols. 

It’s important to note that Hypoxico systems should only be used in support of a Speed Ascent-style expedition and in collaboration with your mountaineering guide service. Traditional expeditions, which make up the majority of CTSS trips, include ample time for acclimatization, and using these systems may result in unnecessary pre-trip illnesses and a reduced ability to recover from your training.