How will altitude affect riders in this year’s Etape du Tour?

The highest peak this year is Cormet de Roselend, which reaches nearly 2000 meters. Oxygen levels at the top of will be between 16% and 23% lower than at sea level, depending on temperatures and humidity (measured as a partial pressure).

In real terms this means that your climbing speed will be between 16% and 23% lower than it would be at sea level, for the same breathing and heart rate. If you were climbing at 10mph at sea level, your speed would drop to about 8mph at 2000 meters. If your climbing rate was 5mph, it would drop to about 4mph at 2000 meters for the same effort level. You will not be starting at sea level of course, but the effect will be similar.

On the other hand, if were to maintain your speed by means of extra effort, your breathing rate will go up by about 20%, and your heart rate will increase by about 10 beats per minute or so.

It is unlikely that there will be any other serious effects due to altitude at 2000 meters.

Now you have an excuse for slowing down at the top!!