At high altitude, atmospheric pressure is lower, which means that the air contains less oxygen. This makes breathing more difficult because our bodies have to work harder to get enough oxygen to function properly.
At high altitude, there is not "less air" as one might sometimes hear, but the air is simply less dense. This means that the air molecules are more spaced out because the column of air above us is shorter and therefore exerts less atmospheric pressure. At sea level, this pressure is about 1013 hPa (hectopascal), while at the summit of Mont Blanc (4,810 m), it drops to around 540 hPa, almost half! This decrease directly affects the availability of oxygen, and this is the main challenge for our bodies: the air we breathe still contains about 21% oxygen, but since the air is overall less dense, each breath allows us to take in significantly fewer oxygen molecules. Our bodies therefore receive a reduced amount of oxygen, which explains why breathing becomes more difficult at high altitude.
At high altitude, even though the air still contains about 21% oxygen, the reduction in atmospheric pressure significantly decreases its availability for our lungs. Simply put: the higher you go, the lower the air pressure, and the less oxygen easily reaches the blood. As a result, each breath brings a significantly lower amount of oxygen than your body is accustomed to at sea level. Even when breathing deeply, the blood struggles to capture enough oxygen, which quickly puts the body in difficulty. This lack of available oxygen is called hypoxia, and it forces your body to work harder to compensate for this deficit.
When climbing to higher altitudes, breathing often becomes a bit more complicated. The body quickly senses that it is lacking in oxygen, so it compensates by accelerating the breath. As a result, we breathe faster and deeper: consequently, we use more respiratory muscles, and that leads to fatigue quickly. The heart also speeds up to send oxygen-rich blood to the muscles and organs more rapidly. This requires more energy, which is why we sometimes feel short of breath and an increased heart rate when exerting ourselves at altitude. Fatigue sets in much more quickly than at lower altitudes, even for small tasks that previously seemed simple.
At high altitude, your body quickly becomes disoriented: it receives less oxygen, which translates into an immediate feeling of shortness of breath. No matter how hard you breathe, you feel like you're still short of air. Soon, you feel tired, maybe even a bit dizzy. This is simply because your brain is receiving less oxygen and has to work harder to compensate. Your heart rate increases, you feel stronger and faster beats, in order to send the little available oxygen to your muscles and essential organs. Sometimes, you might even have a headache or feel nauseous: these are very clear signals that your body is struggling to adapt to these unusual conditions.
The human body has this incredible ability to gradually adapt to lower oxygen levels. As soon as we ascend to higher altitudes, the kidneys activate to release a hormone called erythropoietin (EPO). This hormone stimulates the production of red blood cells, our preferred transport method for oxygen. Little by little, the blood becomes capable of carrying more oxygen despite the decrease in atmospheric pressure. The respiratory rate also naturally increases, in order to take in more air, even though each breath is less dense in oxygen. Often, we also notice an increase in the number of small blood vessels called capillaries: this helps to better distribute oxygen to our muscles and other tissues. After a few days spent up there, the cells also become more efficient at using their available oxygen reserves. The result: we breathe better, we tire less quickly, in short, we gradually find our footing at altitude.
To simulate high-altitude conditions and prepare their bodies for exertion in the mountains, some athletes sleep in hypoxic chambers that artificially replicate an oxygen-poor environment.
Some populations, particularly the inhabitants of the Andes or Tibet, exhibit unique genetic adaptations that enable them to breathe better at high altitudes and minimize the effects of oxygen deprivation.
Unlike a common misconception, the concentration of oxygen (about 21%) remains almost constant regardless of altitude. It is the decrease in atmospheric pressure that makes this oxygen less available to your body.
The highest permanently inhabited city in the world is La Rinconada, located in Peru at an altitude of about 5,100 meters. At this altitude, the atmospheric pressure is only about half of what it is at sea level!
Yes, some people may be more vulnerable: those with heart, lung, or neurological diseases, pregnant women, or individuals with a history of severe altitude sickness. These individuals should be particularly vigilant and seek advice from a doctor before any travel or activities at high altitude.
The acclimatization process begins within the first few days spent at high altitude, but a period ranging from a few days to several weeks may be necessary for full adaptation. Generally, it is believed that one week allows for sufficient adaptation to moderate altitudes (up to 4,000 meters); however, it can take longer depending on the individual circumstances.
Acute mountain sickness (AMS) is the body's response to a lack of oxygen at high altitude. Its symptoms include headaches, fatigue, dizziness, nausea, and sleep disturbances. If these symptoms occur, it is recommended to descend to a lower altitude and rest.
A gradual acclimatization is the best means of prevention. Staying well-hydrated, ascending slowly to higher altitudes, avoiding excessive physical exertion in the first few days, and possibly using medications recommended by a doctor are all effective strategies.
The effects of altitude begin to be noticeable at around 2000 to 2500 meters, but this varies among individuals. Beyond 3000 meters, symptoms often become more pronounced and require a gradual adaptation of the body.
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