Training at altitude: what really changes

Whenever someone asks me “does training in the mountains really make a difference?”, my answer is always the same: it depends on what you mean by “in the mountains”. There is a big difference between a walk at 1,200 metres and a climb that takes you above 2,500-3,000, and that is where the body starts working in a different way.

What happens above 2,000-2,500 metres

Above this threshold the partial pressure of oxygen drops, and the body has to carry out the same amount of work with less oxygen available per litre of air. The first responses are acute: breathing rate goes up, heart rate goes up at the same perceived intensity, and fatigue sets in sooner. It is not in your head, it is physiology.

With repeated exposure (days, not hours) the real adaptations begin: more red blood cells are produced, the available oxygen is used more efficiently, and muscle capillarisation changes. But these adaptations need time — we are talking weeks, not a weekend in a mountain hut — and above all they need to be planned, not endured.

Sleep high, train low

The principle that has stood the test of time best is live high, train low: spend many hours a day at altitude — sleep included — to trigger the adaptations, but come down for the quality sessions, where you need to be able to push at your real pace.

The logic is simple. The stimulus for adaptation is the time spent exposed, not the intensity of the training done up there. Training hard at altitude, on the other hand, means working at lower power for the same effort: you pay the price of hypoxia without collecting the benefit. The hours that count are the ones spent at altitude at rest, and you need a good many of them a day for weeks — not two nights in a hut.

For people who live on the plains and cannot move, the realistic version is different: do not chase adaptation, limit the damage. Arrive a few days early when the goal is at altitude, and in the meantime work on what can be trained anywhere — aerobic base, specific strength, tolerance of high ventilation.

The most common mistake

The mistake I see most often, in amateur and competitive athletes alike, is taking the same training load to altitude that you would do on the plains. A body under hypoxic stress needs more recovery for the same session, not the same volume. People who ignore this often arrive at altitude “loaded” and leave it drained, with worse performances in the following weeks rather than better ones.

How I handle it in programming

When I work with an athlete preparing a goal at altitude — be it a ski-mountaineering race, a high-mountain trail or an alpine climb — the programme follows three practical principles:

1. Relative intensity, not absolute. At altitude the reference is not the pace or power you hold on the plains, but heart rate and perceived effort. Asking for the same pace is the recipe for burning out on day two.
2. Lower volume in the first days of acclimatisation, with longer recoveries between intense sessions.
3. Monitoring real data — sleep, resting heart rate, perceived exertion — to understand when the body is really adapting and when it is just piling up fatigue.

What almost nobody considers: drinking and eating

At altitude two things outside the training plan change as well, and I see them neglected systematically.

Fluids. The air is dry and very cold, and you ventilate much more: a significant amount of water leaves simply through breathing, without you perceiving it as sweat. You end up dehydrated without ever really feeling thirsty, and dehydration makes everything else worse — sleep included, which at altitude is already more fragmented on its own.

Carbohydrates. With less oxygen available the body shifts towards carbohydrates, which yield more energy per litre of oxygen consumed than fat does. In plain terms: at altitude you burn through glycogen faster at the same pace, and a fuelling strategy that held up on the plains may no longer be enough. I wrote about how this mechanism works — and about how much sugar you can actually absorb in an hour — in the article on energy systems.

Then there is a chapter that goes through a doctor and not through me: making red blood cells needs iron, and people who start with low stores do not adapt much however long they spend at altitude. If you are planning a serious block at altitude, a blood test beforehand is one of those things worth more than any session.

This is also why I use myself as the first test bench: you can find the theory of hypoxia in any exercise physiology textbook, but knowing how it translates into a real week of training, with heavy legs on day three, is another matter. It is the difference between knowing something and having lived it.

If you are preparing a goal that will take you to altitude — a race, a demanding trek or an alpine climb — it is worth building a plan that takes these mechanisms into account, rather than improvising when you reach the hut.