In at least one embodiment, a device for controlling and/or regulating a training and/or rehabilitation unit comprises a training and/or rehabilitation unit, a sensor unit having sensors for determining oxygen concentration and for determining carbon dioxide concentration, a control unit for the sensors, a microcontroller in the control unit for controlling the heating power of heating elements of the sensors, depending on breath flow volume, for maintaining constant sensor temperatures, and a resistance and/or braking arrangement of the training and/or rehabilitation unit that can be controlled and/or regulated based on a breathing gas composition determined by the sensor unit. The device can be used to increase endurance, preferably by way of altitude training.