High Trails & Thin Air

Last weekend, I swapped sea level Stockholm for sky running in the heart of the Pyrénées Catalanes. We were invited by Nicolas Remires, founder and head coach of Envol, who recently relocated with his family to Les Angles, a quiet ski resort perched at around 1,650m, just a short drive from the iconic high-altitude training hub of Font-Romeu.

Nicolas has been quietly laying the groundwork to turn Les Angles into a new Envol training base, and this weekend felt like the start of something special. With a group of Envol members from Sweden and France, we gathered for a weekend of trail running, community, and mountain air - blending training with adventure in a place that feels both wild and welcoming.

Under clear alpine skies, we explored high ridges, pine-lined switchbacks, and single track climbs. It was more than just a training weekend, it was a chance to connect, recalibrate, and experience the rhythm of high-altitude living.

Les Angles: A Hidden Gem at Altitude

Les Angles is better known for skiing, but come spring, the snow gives way to rolling trails, open roads, and a peaceful alpine atmosphere, ideal for endurance work. With direct access to mountain terrain and minimal distractions, it offers a slower pace that’s perfect for focused training blocks.

We stayed at Chalet Azimut, a fantastic base for a training group. Comfortable, spacious, and well-equipped for athletes, it had everything we needed. The views didn’t hurt either. If you’re planning a group camp, it’s definitely worth checking out.

Just 20 minutes away, Font-Romeu offers more structure: a dedicated athletics track at 1,800m, a full INSEP training centre, and a proud legacy of hosting Olympic athletes. But with Les Angles offering so many great trails we didn’t make it over, I’ll save that for another trip.

Did You Know?

Font-Romeu has been one of Europe’s top altitude training destinations since the 1960s. It’s home to the CNEA (Centre National d’Entraînement en Altitude), used by France’s national teams, Olympic athletes, and professionals across endurance sports. The town sits at 1,800m and features a high-altitude athletics track, swimming facilities, gym, and hypoxic rooms. Kilian Jornet, Paula Radcliffe, and the French national triathlon team have all trained here.

Is It Worth Coming Just for a Long Weekend?

If you’re hoping for major physiological changes, the answer is no, three days isn’t long enough to trigger real red blood cell gains.

But that doesn’t mean it’s not worthwhile.

Even a short visit gives you:

• A mental reset and new training stimulus

• Exposure to how your body responds to altitude

• A chance to test pacing, hydration, and nutrition strategies

• Valuable shared experience with teammates or training partners

For many athletes, a weekend at altitude can be a learning lab, and often the first step toward planning a longer, more structured camp.

What Happens to the Body?

As elevation rises, oxygen availability drops. Your body responds by ramping up red blood cell production, improving oxygen delivery and endurance efficiency. But this doesn’t happen immediately. Initial exposure can feel tough:

• Heart rate and breathing increase

• Recovery slows

• Sleep may be disrupted in the first few nights

With time, though, the body adapts, and those adaptations can translate into improved performance when you return to sea level.

Altitude and VO₂ Max: Why You Slow Down

One of the biggest reasons training feels harder at altitude is the drop in VO₂ max, your body’s ability to take in and use oxygen efficiently.

Research shows that for every 300 meters of elevation gain above 300 meters above sea level, VO₂ max drops by about 1.9%. That might not sound like much, but it adds up fast.

At 1,800 meters (the elevation of Font-Romeu, and easily reached from Les Angles):

• You’re roughly 1,500 meters above the "safe" 300m baseline.

• That translates to about a 9.5% reduction in VO₂ max compared to sea level.

In simple terms, the higher you go, the harder it gets to sustain the same speed or intensity, because your body is working with less oxygen.

This is why two runners, equally fit at sea level, might perform very differently when racing or training at altitude, individual variability also plays a big role, with some athletes adapting better than others.

Training Paces at Altitude

Here’s a rough guide:

Important: This is a rough guide. Always listen to effort, heart rate, and recovery, not just your watch. Some athletes slow down even more early on before adapting.

Live High, Train Low - Ideal, But Not Essential

One well-established strategy is Live High, Train Low (LHTL). The concept:

• Live and sleep at high altitude to stimulate adaptation

• Train at lower elevation to maintain workout intensity

Elite athletes often build entire camps around this approach:

• Sierra Nevada (Spain): Live at 2,300m, train in Granada (680m)

• Flagstaff (USA): Stay at 2,100m, train in Sedona or Phoenix

• St. Moritz (Switzerland): Live at 1,800m, train along lower valley trails

In Font-Romeu or Les Angles, LHTL is possible with a bit of planning. You can descend 50–60 minutes to Prades or Quillan (~300–400m) for quality sessions in denser air. While not daily, these excursions work well for key workouts.

That said, some of the world’s best endurance athletes train entirely at altitude.

• In Kenya, runners in Iten (~2,400m) live and train high every day.

• In Ethiopia, athletes train near Addis Ababa (2,300m) or even higher, in Sululta or Entoto.

These runners build aerobic strength, economy, and mental resilience by training consistently at elevation, without needing to descend. So while LHTL is ideal in some settings, training high, living high works too, and Les Angles is a great example.

Takeaways from Our Weekend

The days and route options were very well planned so that the group could both stay together and allow for additional kms for the ones that wanted it; getting in a total of between 50 and 70km during the days. Fantastic dinners together in the evenings at Chalet Azimut prepared by the proprietor (and monoskiing legend) Laurent Casa were a great way to bring the group closer together.

One personal observation was that my heart rate was unusually high on Day 1 even during easy efforts. But by Day 2 and 3, it had settled. Since I couldn’t have acclimatized that quickly, I suspect dehydration was a big factor. Once I focused on drinking more, the numbers improved.

Other contributors may have been travel fatigue, poor sleep, and that subtle buzz of adrenaline that comes from being in a new environment with a motivated group. It was a good reminder that the first session at altitude shouldn’t be a test, it should be a tune-in. Give your body a chance to adjust before pushing.

If you're heading to altitude, even just for a few days, here are a few acclimatization tips I’d recommend:

• Ease into intensity. Keep the first 48–72 hours low-key. Let your body settle before you go hard.

• Hydrate more than usual. Dry air and increased breathing rate mean you lose more fluids.

• Sleep is performance. Recovery takes a hit early on, so protect your rest.

• Check iron status. Especially for longer camps, low ferritin can limit your adaptation response.

• Stay flexible. Elevated heart rate, mood dips, and fatigue are normal, adjust training accordingly.

What stood out most, though, was the camaraderie. Running, eating, and recovering together in the mountains reminded me how much value there is in shared training. The altitude adds stress, but it also deepens the sense of purpose.

Should You Train at Altitude?

It’s not for everyone, but if you’re preparing for a big race, or just want a block of focused, high-quality aerobic work, a trip to altitude can be incredibly effective.

Ask yourself:

• Am I fit enough to absorb the added stress?

• Am I okay adjusting my pacing and expectations?

• Do I have a coach or plan to guide me?

If the answer is yes, Les Angles offers an accessible and rewarding environment to challenge your physiology and mindset alike.

Final Thoughts

There’s something powerful about training where the air is thin and the goals feel big. Whether you're looking for a performance edge, a deeper connection to your training, or just a new perspective, a high-altitude camp can deliver all of that, and more.

Even if it’s just for a weekend, don’t underestimate the value of getting out of your usual routine and running among the peaks.

Until next time, breathe deep, run strong, and keep reaching higher.