The technique know as Intermittent Hypoxic Training (IHT), whereby oxygen levels of between 10 and 15 per cent (equivalent to an altitude range of 2500-6000 metres) are administered by a machine known as a Hypoxicator, which separates air through a semi-permeable membrane. The person is asked to breathe the high-altitude air for just a few minutes at a time while their blood oxygen levels are continuously monitored. They then breathe ambient or normal air for a few minutes, giving their body time to adjust back to normal conditions. The time spent alternating between low-oxygen air and normal air is 60 to 90 minutes at a time. The procedure is generally carried out once or twice a day for a total of 16 to 30 sessions.