 This study examined the effective altitude on the performance of highly trained ski mountaineers. The results showed that the athlete's maximal oxygen consumption, VO2 max, maximum heart rate, and oxygen pulse decreased significantly when they ascended to higher altitudes. Additionally, their ventilatory threshold also decreased, meaning that it took less effort to reach the same level of exertion. These findings suggest that highly trained athletes should be aware of the potential impacts of altitude on their performance and adjust their training accordingly. This article was authored by Isabelle Schoffel, Bernhard Bliemsreeder, Thomas Kupper, and others.