The invention relates to a device for performing respiratory training, in particular altitude training, comprising a mouthpiece (1) through which a person can exhale respiratory gas into a volume (2, 3a, 7) or can inhale it out of the volume (2, 3a, 7), wherein this volume (2, 3a, 7) is formed at least in part by a container (2) which is adjustable in terms of its volume and which is connected to the mouthpiece, wherein the volume (2, 3a, 7) adjoins one side of at least one gas-permeable membrane (4), to the other side of which at least one gas exchange chamber (3b) is connected, through which a fluid provided for the gas exchange, in particular CO2 and/or O2 gas exchange, can actively flow. Furthermore, the invention also relates to a method for performing respiratory training, in particular altitude training, wherein a person exhales into a training device through a mouthpiece (1) and inhales from this training device, wherein the O2 and/or CO2 partial pressure in the respiratory gas inhaled from the device is influenced by exchange of O2 and/or CO2 between the respiratory gas in the training device and a fluid provided for the gas exchange through at least one gas-permeable membrane (4).
