Acclimatization is a very important but sometimes underestimated topic for mountaineers. Climbing high mountains is a burden for the body. In this article we examine how you optimally prepare your physiological system to get along with the altitude and the lower oxygen partial pressure.

Physiological acclimatization changes

Why is acclimatization that important? Because it’s the only natural solution to the main problem on the mountain: Altitude sickness. In higher altitudes the air pressure decreases. Thus, the oxygen partial pressure declines as well. That means, you inhale less oxygen in one breath. With oxygen being the basis for the whole cardiovascular system, high altitudes withdraw the body its main energy source. Without proper acclimatization, that can cause serious – sometimes life threatening – problems. However, through acclimatization the body can adapt to these challenging conditions. It induces physiological changes that make the absorption and processing of oxygen more efficient.

Some of these changes include deeper respiration and a higher breathing and heart rate. Besides, the body produces more red blood cells that carry the oxygen to the tissues. In addition, the body creates more of a particular enzyme that facilitates the release of oxygen from the red blood cells to the tissues. All these bodily adjustments serve the purpose of bringing more oxygen to the tissues.

Don’t go too high too fast

The body needs time to adapt to higher altitudes. That’s why you should do a smooth transition. Ascending slowly is the key principle of acclimatization. If you go too fast, you overwhelm your body. As a rule of thumb, above 3.000 m (9.843 ft) you should only increase your sleeping altitude by 300 m (984 ft) to 400 m (1312 ft) per day. Furthermore, for every 900 m (2.953 ft) elevation you should take a rest day. If you are an experienced mountaineer with a sound feeling for his capacity to deal with high altitudes you can of course deviate from these rules.

Moreover, you should literally go slowly. High altitudes strain your body. That’s why you shouldn’t overload it by going too fast. On the high mountain you should avoid anaerobic efforts as best as possible. How do you know whether you are in an aerobic or anaerobic state? Generally, if you are able to talk with your partner while walking, you are still working aerobically.

This rule also implicates that you have to acclimate your body to high altitudes by starting with climbing lower mountains and then gradually increasing the height. For example, if you want to climb the Chimborazo you have to ascend smaller mountains like the Rucu Pichincha before. In this preparation phase you can follow the “climb high, sleep low” rule.

Climb high, sleep low

In the context of acclimatization there is a common concept called “climb high, sleep low”. As the name suggests, it recommends to ascend mountains during the day but to come back down afterwards and sleep at a low altitude at night. It’s not the maximum altitude during the day that is crucial. It’s rather the sleeping altitude. Why? Because it determines the quality of your sleep. The problem of sleeping high is that your sleep quality suffers from the increased heart rate and other symptoms like headache. “Climb high, sleep low” trains your body for high altitudes but also gives you a good regenerative sleep.

Sleep high, train low

“Sleep high, train low” is a concept that is predominantly useful for athletes. In contrast to the last principle, this one focuses more on a qualitative workout than on a deep sleep. Training low gives your body the necessary oxygen to perform an intense high-quality workout. In extreme altitudes, training is difficult. Simultaneously, sleeping high induces physiological acclimatization processes (like enhanced red blood cell production). That is beneficial for athletes because the higher efficiency of oxygen transport to the tissues increases the athletic performance.

Other acclimatization tips

Drink lots of water! The high altitude stresses the body. As a result, it uses more water. Make sure to fill your body up again. Adding about an extra liter is a good rule of thumb. In addition, you should adjust your nutrition. Carbohydrates give your body the necessary energy. That’s why carbohydrates should take up 70% or more of your calories in high altitudes. Moreover, you better avoid tobacco and alcohol on the mountain.

Besides, it can help to sleep with the upper body slightly facing upward. In addition, good air ventilation while sleeping is important. You want to get as much oxygen as possible into your sleeping room.

Furthermore, checking your resting pulse can give you an orientation of how heavily your body is engaged in the acclimatization process. If your resting pulse is at least 20% higher than normally, you are in the critical acclimatization phase. That means, your body is adapting to the high altitude. It’s implementing the physiological changes that support the absorption and transportation of oxygen. When the pulse comes back to normal you completed the acclimatization phase for this specific level of altitude.

Besides, you can use a pulse oximeter to get an even better idea of what is happening in your body. Pulse oximeters measure your arterial hemoglobin oxygen saturation. That basically means how much oxygen is in your blood. How? The oximeter uses the phenomenon that oxygenated and deoxygenated hemoglobin absorb light differently. The device projects light of specific wavelengths through your finger. After passing through it a photodiode detector measures the intensity of the light on the other side of the finger. Based on how much light was absorbed by the finger the oximeter calculates your oxygen saturation. That gives you an indication of how well your body is responding to the altitude. Nowadays, there are small and precise devices available that don’t cost much.

Don’t go up until symptoms go down

Nevertheless, everybody is susceptible to altitude sickness. Even if you follow all the tips above. So, what do you do if you suffer from altitude sickness? If you get a headache, nausea or dizziness? That depends on how bad your symptoms are. With light altitude sickness symptoms you should stop your ascend and wait until it gets better. Talk to your guide and your group. They will probably understand you. Listen to your body. Don’t overstrain it. Continuing to ascend with symptoms is very dangerous. Only when you feel significantly better, you can go on.

However, if you have heavy symptoms the only option is going down. Since altitude sickness can be life threatening (cerebral oedema, pulmonary oedema) you have to take the symptoms seriously.

Plan your acclimatization

Acclimatizing properly is critical for your climbing success. We can’t stress enough how important it is to take enough time for getting used to the height. You should carefully plan it. Which smaller mountains do you climb before ascending the big ones? At which altitude do you sleep? How fast do you ascend? You know about the right tools. Now it’s up to you to use them.