The Test of Incremental Respiratory Endurance (TIRE) is a physiological test designed to assess an individual's respiratory endurance. It involves breathing through a device that provides resistance to airflow, typically a hand-held inspiratory muscle trainer (IMT) called a PrO2.

The Test of Incremental Respiratory Endurance (TIRE) was developed in the 1990s as a bedside measure of inspiratory muscle endurance and a through-range inspiratory muscle training protocol. The training and assessment were based upon a novel maximal effort that extended the traditional MIP measure taken at residual volume (RV) and sustained for 1 second to an isokinetic-resisted inspiration from RV to total lung capacity (TLC). This inspiratory performance measure from RV to TLC provided a new measure entitled the Sustained Maximum Inspiratory Pressure (SMIP). It was shown to users as an on-screen effort with a link to a computer interface. The visualization of the SMIP gave biofeedback to users as an on-screen prompt and enabled researchers to judge the integrity of the effort being provided by the user.

During the TIRE protocol, individuals inhale against the resistance, aiming to sustain this effort for as long as possible. The test helps evaluate the endurance and strength of the respiratory muscles, particularly the inspiratory muscles involved in the inhalation process.

This type of test and training is often used in respiratory rehabilitation programs, sports training, and clinical settings to assess and improve respiratory muscle function. It can benefit individuals with conditions affecting respiratory muscles or those seeking to enhance their respiratory fitness.

It is recommended that the TIRE protocol be conducted under the guidance of qualified healthcare professionals or exercise specialists.