The World Anti-Doping Agency (WADA) is considering a ban on the use of altitude tents and altitude rooms, which simulate the low-oxygen atmosphere of high elevations with the aim of encouraging red blood cell production and boosting endurance. WADA's ethics committee deems the widely used training method contrary to "the spirit of sport." As I've said, I don't really understand why performance-enhancing drugs violate "the spirit of sport." But if they do, it is hard to see why performance-enhancing rooms don't. They seem at least as artificial to me; if anything, steroids are more natural.
But saunas, cold soaks, vitamin capsules, and weight training are artificial too. None of these methods is cheating unless it's against the rules. If everyone is allowed to use it, the competition is still fair (leaving aside differences in natural endowments). In fact, banning high-altitude simulations arguably would make contests less fair, giving an advantage to athletes who happen to live at high elevations or who can afford to move there. "Ninety-five percent of the medals that have been won at Olympic Games have been won by people who train at or live at altitude," a running coach tells The New York Times.
I gather that "the spirit of sport" is not synonymous with fairness; it's more of an aesthetic judgment. Still, why would it permit athletes to improve their performance by moving to a mountain but not by retrofitting their bedrooms with a filtering system?