Running in the mountains is, in itself, an act of endurance. Not just physical, but also spiritual. You fight against the uneven terrain, against fatigue, against the inner voice that begs for a cold beer and some shade. But when you add heat to all of that—that invisible tyrant that clings to your skin like a badly repaid debt—the human body becomes a thermodynamic experiment on legs.
And yet, heat can be tamed. Not extinguished, of course. But we can learn to live with it like we live with an uncomfortable father-in-law: with strategy, patience, and a certain amount of resignation. That, in essence, is the heat acclimatization: a forced alliance between the body and the climate to prevent the former from collapsing and the latter from getting its way.
Sweat as a strategy, not as a punishment
The first thing to understand is that acclimatization isn't a miracle: it's methodically applied biology. Trail runners don't just train to run; they must also train to sweat better. Because yes: sweating efficiently is a thermal superpower. Through sweat, the body learns to cool itself with less wear and tear, to keep its internal machinery functioning without overheating like a coffee pot left on the stove.
How is this achieved? Through the repeated exercise in heat, which can be natural (training at midday in the middle of August) or artificial (saunas, climate chambers or even hot baths after running). The key is in the progressive heat stress: It's not about committing suicide in a climb below 40°C, but about going increasing intensity and duration with intelligence. Like teaching a cat to tolerate water: slowly, patiently, and without being scratched.
The rules of the (hot) game
For the first 3 or 4 days, it's best to train at a moderate intensity (60-70 minutes) and no more than 90 minutes. Then, increase the volume, because one of the most powerful adaptations occurs when you can go from 100 continuous minutes of running in the heat, without feeling that he has entered hell with no return.
A useful trick? Simulate the exact conditions of the race: the same time, altitude, temperature, humidity level. This way, your body won't be surprised. And although it may seem contradictory, Low intensity and long duration can be as effective as more intense training, as long as thermal stress is maintained.
There's also room for passive methods: a post-workout sauna or hot bath session can be helpful as a complement. It doesn't replace warm-up exercise, but it helps. It's like studying with classical music: it doesn't work miracles, but it sets the mood.
Hydration, the art of drinking without thirst
Here comes one of the cruelest traps of heat: thirst comes late, like certain uncomfortable truths. If you wait until you have it, you're already losing. Hydration must be proactive, almost obsessive. 500 ml before leaving, sips every 15 minutes, and a golden rule upon returning: replace 1.5 liters for every kilo lostYes, you have to weigh yourself. Not out of vanity, but for survival.
And let's not forget the electrolytesIn the first week, they sweat more than pride in defeat. Salt, potassium, magnesium... everything that's lost must come back. Skipping meals during the process is like forgetting your ropes before climbing: unnecessary negligence.
Time is the oven where the habit is baked
Acclimatization is not a matter of a day. Not even a week, in many cases. It is estimated that between 7 and 14 days Continuous exposure is necessary for the body to activate its thermal defense mechanisms: earlier and more efficient sweating, lower heart rate, lower internal temperature. It all sounds technical, but the summary is simple: you suffer less and perform better.
Of course, like any superpower, it's lost if it's not used. After 7 days without heat, adaptations begin to fade like the memories of a party with too much wine. After 3 weeks, the 75% from the effort has evaporated. Therefore, it's advisable to maintain exposure or, at least, make «thermal reminders»: A couple of warm-up workouts before the race are enough to reactivate body memory.
Final reflection: train to avoid burnout
We might think that acclimatizing to the heat is just a strategy to compete better. But it is also, in a way, a metaphor for human resistanceLearning to run under fire—literally and figuratively—is a way to temper the body, yes, but also the character. Because in the mountains, as in life, it's not just about moving forward: it's about not decompose when the environment becomes hostile.
And in that sense, heat acclimatization is much more than a physiological technique. It's an act of wisdom. A way of not giving up… even when the sun challenges you from above as if it has something personal against you.
