Question, when a rider trains at altitude (or sleeps in one of the altitude tents), what altitude are we talking here? Have there been studies on what would be the best altitude? Apparently the highest you can get in the Sierra Nevada's is about 11,500 feet, and you probably aren't sleeping anywhere near that altitude (highest city in Spain is listed as being at just 5553 feet). Alternately you could go to La Paz in Bolivia and live comfortably at 13,500 feet and train a few minutes down the road at 9000 feet. So at what altitude does the benefit plateau?