Abstract: A hypoxic training system is provided that dynamically adjusts the oxygen ratio in the gas provided to the user during a hypoxic training session based on the blood oxygen saturation (SPO2) level of the user. During a first training period, the hypoxic training system provides gas according to a first oxygen ratio. When it is determined that the SPO2 level of the user has reached a target SPO2 level, the hypoxic training system may provide a recovery period, during which gas according to a second oxygen ratio is provided to the user. When it is determined that the SPO2 level of the user has fallen more than a predetermined threshold below the target SPO2 level during the recovery period, the hypoxic training system may provide gas according to an increased first oxygen ratio during a subsequent training period.