Tolerance to exercise at altitude varies considerably from person to person and is not directly related to fitness. Mild symptoms of altitude sickness such as headache and shortness of breath are tolerable, but more severe symptoms like nausea and vomiting indicate the onset of a more serious condition (acute mountain sickness or "AMS", and must be avoided at all costs. For this reason our week is structured to give you the maximum amount of time to acclimatise, going straight to mountain huts of moderate altitude and doing our preparations there. Sleeping height is the key – to acclimatise effectively, at least two nights should be spent at altitude prior to the ascent.

We have found that about 5% of our clients cannot acclimatise sufficiently in a week to reach the summit of Mont Blanc. (See also "Do you run courses of less than 6 days?)