Hypoxia refers to low oxygen conditions. For air-breathing organisms, hypoxia is problematic but for many anaerobic organisms, hypoxia is essential. Hypoxia applies to many situations, but usually refers to the atmosphere and natural waters.
Still frame from an underwater video of the sea floor. The floor is covered with crabs, fish, and clams apparently dead or dying from oxygen depletion.
Jubilee photo from Mobile Bay
Altitude training is the practice by some endurance athletes of training for several weeks at high altitude, preferably over 2,400 metres (8,000 ft) above sea level, though more commonly at intermediate altitudes due to the shortage of suitable high-altitude locations. At intermediate altitudes, the air still contains approximately 20.9% oxygen, but the barometric pressure and thus the partial pressure of oxygen is reduced.
Altitude training in the Swiss Olympic Training Base in the Alps (elevation 1,856 m or 6,089 ft) in St. Moritz.
Altitude training in a low-pressure room in East Germany