A respiratory muscle endurance training device (RMET) includes a chamber and a patient interface. In one implementation, one or both of a CO.sub.2 sensor or a temperature sensor can be coupled to the chamber or patient interface to provide the user or caregiver with indicia about the CO.sub.2 level in, or the temperature of, the chamber or patient interface, and/or the duration of use of the device. In another implementation, the RMET may have a fixed volume portion adjustable to contain a measured portion of a specific patient's inspiratory volume capacity. Methods of using the device are also provided.