The purpose of this study is to investigate whether a diaphragmatic breathing exercise using the air stacking technique can improve respiratory function and trunk control in patients with stroke. The experimental group will perform an air stacking-based diaphragmatic breathing exercise using an Ambu-bag, combined with neurodevelopmental treatment, three times per week for 20 minutes over a 4-week period. The control group will receive therapist-guided diaphragmatic breathing exercises with the same frequency and duration, together with the same neurodevelopmental treatment. All participants will be assessed before and after the intervention for pulmonary function, chest wall expansion, and trunk control ability, as well as the Korean version of the Trunk Impairment Scale (K-TIS), the Five Times Sit-to-Stand Test (FTSTS), and the Borg Rating of Perceived Exertion (Borg RPE). Changes between the two groups will be compared to determine the therapeutic effectiveness of the air stacking technique.