How to Prepare for High-Altitude Mountains

Climbing summits like Pico de Orizaba, Iztaccíhuatl or Nevado de Colima often seems like a mystery to someone just starting to chase that challenge. It isn't so much: most of the work happens months before summit day.

Here are the points that weigh most. They're general tips, adaptable to each mountain and each person. We also explain what altitude sickness is, how to recognize it and what to do if it appears, because preventing it is a core part of the preparation.

High-altitude mountaineering is generally considered above 4,000 meters above sea level, though altitude sickness can begin as low as 1,500 m. At its core it's a problem of hypoxia: it's not that oxygen disappears, but that at higher altitude the atmospheric pressure is lower, so the body has to work much harder to capture it, roughly twice as hard on Pico de Orizaba and up to three times on Everest.

The Society of Mountain Medicine divides altitude into three zones:

• High altitude: 1,500 to 3,500 m.
• Very high altitude: 3,500 to 5,500 m.
• Extreme altitude: above 5,500 m.

The effect is progressive and doesn't discriminate by fitness level: an estimated 75% of unacclimatized people show some symptom at 3,000 m. Since the brain is the organ that consumes the most oxygen, almost all the discomfort reflects its reduced performance.

The mild symptoms are ones almost all of us experience: shortness of breath on exertion, headache, fatigue, loss of appetite and thirst, nausea, trouble sleeping, vision problems and an elevated heart rate. Certain conditions, such as anemia, increase the risk.

The severe symptoms are a red alert:

• Difficulty breathing even at rest.
• Confusion and disorientation.
• A cough that may bring up blood.
• Pale or grayish skin.
• Vertigo.
• Very important, social withdrawal: when someone says 'go on without me, I'll rest here'.

Pulmonary edema and cerebral edema can be fatal. The problem is that often the person suffering it doesn't know it: they think they're just tired. If you leave them there to rest, they may rest forever.

When someone starts to feel sick on the mountain, the best thing is to descend. It's the only truly foolproof remedy. With pulmonary or cerebral edema, recognizing it in time is crucial: the first signs are usually an uncontrollable cough, a sensation of bad breath and poor aerobic performance. If they appear, descend immediately and seek urgent medical care; during that phase, avoid sleeping pills, alcohol and exercise.

There are medications used for acclimatization or to treat emergencies (acetazolamide, dexamethasone, nifedipine, salbutamol, sildenafil, oxygen), and on some mountains guides carry portable hyperbaric chambers or oxygen tanks, but their use must always be guided by medical judgment. None of them replaces the golden rule: with severe symptoms, go down.

Note: this text is educational content based on mountaineers' experience and medical sources; it does not replace professional advice. Consult a doctor before your expedition.

For almost any ascent there is specific information about the trail you'll take. It's well worth learning as much as possible about the environment you'll face: ask those who have already gone and look for reports online.

For the trail we recommend Wikiloc, where you'll find tracks, comments and warnings from other hikers. For the weather, sites like Mountain Forecast give forecasts by altitude, which is what really matters in high mountains.

The first symptoms of mountain sickness usually start with fatigue, so a good aerobic base is your best ally as you approach altitude. Very relaxed activity (jogs where you can hold a conversation) increases your capacity to handle oxygen and eases the physiological adaptation process. General strength exercises help, especially squat, lunge and deadlift variations.

And the most useful thing: experience similar conditions. If you train from Monterrey, take advantage of the mountains nearby. Climb hills with the same gear and the same loaded backpack you'll use in the high mountains, to build up your back muscles and get your body used to the weight. And to really test how your body reacts to altitude, go to Arteaga, where there are mountains above 3,500 m such as La Viga, La Marta or Las Nieves.

We recommend doing part of that training alone. You can go with others, but ask them not to talk, or walk a few meters apart.

Why? Because on the mountain you'll have to deal with that version of yourself telling you not to go up, that you can't, that you'd better turn back. And you'll be the one who has to win that argument, several times, with no one to fight it for you. A good way to forge that mindset is to do hills that take about as long as the big day, more than 10 hours for the full route, like La Tía Chena, El Viejo or El Potosí. Learning to keep going when your body is already tired is half the battle.

The best prevention is proper acclimatization: giving the body time to reach a balance as it climbs. According to the UIAA, the ideal is to sleep at altitudes that rise no more than 500 meters per night, so the body adapts and produces more red blood cells in response to the lack of oxygen.

A point that's often misunderstood: where you sleep matters more than the highest point you reached that day. Adaptation is a matter of exposure time. That's why the most useful technique is to climb high and sleep low: during the day you go up to expose your body to less oxygen, then come down to sleep at a lower altitude, where it can hydrate, eat and rest well. And that's why it's worth arriving 3 to 7 days early, so adaptation happens calmly and not abruptly during the ascent.

Rest is the third pillar, and it's not enough to lie down: you have to actually sleep. If you climb too fast and don't sleep, you don't recover and become more prone to mountain sickness. Prioritize sleep even if that means climbing more slowly; slow but steady.

It's the most underestimated factor. In the cold we think we don't sweat, but up there the pressure is lower, the air is extremely dry and you're almost always below freezing: while breathing and even talking you constantly lose moisture, and you dehydrate very fast without feeling it (a clear sign is that you start peeing very yellow).

The recommendation is to drink between 3 and 4 liters of water a day, even when the altitude closes off your appetite and thirst. You have to be disciplined: hot water, tea, water with honey or sugar, whatever it takes to reach that amount. At base camp there's sometimes a river; higher up you'll have to melt snow, always from a clean area.

Before the ascent: some studies suggest that eating iron-rich foods helps acclimatization. Even so, that correlation matters less than keeping a balanced diet and constant hydration.

During the ascent: it's vital to know what you'll eat. It's not enough for it to be nutritious; you have to know the effect it has on your digestive system. Gastrointestinal problems are one of the most common reasons for not reaching the summit. That's why, in every training session, bring the food and drinks you plan to use on summit day and pay attention to how your body reacts.

One extra note on what to eat up high: with less oxygen the stomach digests more slowly and greasy or heavy food sits worse, so a diet high in carbohydrates is best, as the body metabolizes them quickly and they're direct fuel for the brain. Bring something you love to eat so you can get started even when you're not hungry.

The first time you visit a high mountain, complications can arise. Go with caution and stay attuned to how your body reacts, because it doesn't know that environment.

Knowing your limits is what lets you come down in good shape. It's worth understanding that the body is a tool and that at any moment something can go wrong, leaving you with a single sensible option: turn back, train and try again. The mountain is a hostile environment and it doesn't care who you are; it will throw its worst conditions at you, and it's up to you to arrive with the skills to deal with altitude sickness, extreme winds, dehydration, hypothermia and more.