Allow at least five to seven says to acclimatize to the altitude at which the race will take place. Be conservative in getting up and over uphills. Drink as much as possible during the event. By incorporating all of these strategies, it is indeed possible to run ultras at altitudes as high as 10 to 12,000 feet. A Report on the Western States 100 Mile by Don Allison Ultra Running Tips Hike in small groups rather than alone.
Persons running or moving rapidly are at higher risk.