In those with COPD, PEP acts as a “pneumatic stent” to maintain airway patency during exhalation and prevent dynamic hyperinflation. Approximately 80% of individuals with COPD experience air-stacking known as ‘dynamic hyperinflation’ during exertion and day-to-day activities. Hyperinflation puts the respiratory muscles and diaphragm at a mechanical disadvantage and stretches them; these muscles don’t like to be stretched which leads to the sensation of breathlessness and feeling of discomfort by individuals with COPD. PEP helps reduce the expiratory collapse of small air tubes and decreases air trapping, thereby, reducing the feeling of shortness of breath.