Altitue training traditionally referred to as altitude camp, is the practice by some endurance athletes of training for several weeks at high altitude, preferably over 2,500 m (8,000 ft) above sea level, though more commonly at a lower altitude due to the lack of availability of a suitable location. At this altitude the air still contains approximately 20.9% oxygen, but the barometric pressure and thus the partial pressure of oxygen is reduced.. More common nowadays is the use of an altitude simulation tent, altitude simulation room, or mask-based hypoxicator system where the barometric pressure is kept the same, but the oxygen content is reduced which also reduces the partial pressure of oxygen. Such devices have enabled different altitude training techniques including Live High, Train Low, or the practice of merely performing occasional exercise sessions at altitude.