Topics discussed in this article include methods and results of inspiratory muscle training and inspiratory muscle rest. The role of inspiratory muscle training remains controversial. No study has shown conclusively that improving inspiratory muscle strength and endurance will decrease CO₂ retention. Likewise, no study has shown that inspiratory muscle training is superior to other treatments in increasing a person’s ability to perform a particular task or activity of daily living. To be recommended to patients on a long-term basis, improvement in inspiratory muscle strength or endurance should be shown to be associated positively with a reduction in a person’s morbidity and mortality or an improvement in their ability to perform activities of daily living or vocational tasks.