Cycling at altitude: what are the consequences for breathing and performance?

Performing at high altitudes is more difficult than on flat terrain. Why is breathing restricted at altitude, and how does it reduce our performance? Here are some insights.

By Pierre-Maxime BRANCHE. Photos: Pxhere, ASO, Paulo Maria / DPPI

Breathing at high altitudes is not inherently violent, yet the lack of oxygen constitutes a real assault on the body, which must immediately react and adapt to this new environment. Metabolically, altitude causes an increase in red blood cells, which increases blood viscosity, making it richer and thicker. It then becomes more difficult for the blood to reach small irrigation channels, especially those in the brain, which can lead to some discomfort.

For example, this is the case for some people who take the Aiguille du Midi cable car in Chamonix, stay a few hours perched at 3,842 m altitude, and quickly suffer from nausea and headaches. To counteract this viscosity, it is essential to drink regularly to thin the blood. In the context of high-altitude sports, more than breathing itself, it is oxygen consumption that is the limiting factor for performance, hence VO2Max (Maximum Volume of Oxygen Consumption).

A decrease in VO2Max from 1,200 m

Oxygen consumption is indeed exponentially limited at altitude, meaning that, generally, at the summit of Mont Blanc (4,810 m), one loses about 30% of their aerobic capacity. Beyond that, it drops even more rapidly, although one never cycles at such altitudes, at least in France. However, there is also a decrease in VO2Max at lower altitudes, for everyone, athletes or hikers. Thus, VO2Max decreases from 1,200 m. At 2,000 m, this decrease reaches 5% of maximum aerobic capacity, and 15% at 3,000 m. As a reminder, the Col du Galibier, for example, culminates at 2,642 m and will thus strongly force your body to adapt if you arrive from Lyon, Dijon, or Strasbourg. Naturally, activities that require a high VO2Max, such as cycling or trail running, are penalized, because to capture the same number of oxygen molecules, a larger volume of air will need to be moved. Since the blood is not 100% saturated, the body cannot express its full capacities. Few world records, across all disciplines, have been broken at altitude, except those where air penetration plays a role, such as the track cycling hour record, the last mark of which was set by Belgian Victor Campenaerts on April 16, 2019, in Aguascalientes (Mexico) at… 1,885 m. Because between loss of VO2Max, adaptation, and reduction of air penetration coefficient due to altitude, there is, of course, a compromise to be found.

Minimum fifteen days

Most people think that by going to altitude, performance improves. This is both true and false. Indeed, certain capacities or energy systems can be improved, especially in aerobic activities. This is the case for trail runners, triathletes, and cyclists, but it is not systematic as it also depends on each individual. If one seeks to improve performance by going to altitude, one must first accept to acclimatize, which takes about ten days. Then, one must resume training adapted to the mountain environment. This “altitude” operation therefore requires a large investment in terms of time and thus resources, unless one has their own chalet in the mountains.

This is a real issue because, on the one hand, many teams and federations go to altitude to improve their athletes’ performance, and on the other hand, numerous scientific publications explain that not everyone reacts the same way at altitude, question the real benefits of altitude training, and specify that one must first think on an individual level: some athletes will find benefits, others will not. Finally, when we hear about altitude training camps, for example, for team sports that go there a week before major international competitions, it is important to keep in mind that this time is not long enough to derive any benefits, because a minimum of fifteen days, or even three weeks, are necessary to carry out real quality work. But in this case, these are often communication or advertising strategies, particularly at the initiative of resorts.

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