Intermittent hypoxic therapy
Intermittent hypoxic therapy, also known as intermittent hypoxic training (IHT), is a technique aimed at improving human performance by way of adaptation to reduced oxygen. An IHT session consists of an interval of several minutes breathing hypoxic (low oxygen) air, alternated with intervals breathing ambient (normoxic) or hyperoxic air.
Source: Wikipedia — Intermittent hypoxic therapy (CC BY-SA 4.0)