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.

This clinical trial is a randomized controlled study designed to evaluate the effects of a diaphragmatic breathing exercise using the air stacking technique on respiratory and trunk function in patients with stroke. Patients with stroke are prone to respiratory muscle weakness, reduced chest wall expansion, and impaired trunk control, which can limit functional recovery and increase the risk of pulmonary complications. The air stacking technique increases lung volume and chest expansion through consecutive inspirations without exhalation and is known to facilitate more effective breathing and coughing, but its therapeutic effects in patients with stroke have not yet been fully established.

In this study, 20 patients with stroke will be randomly assigned to an experimental group (n = 10) or a control group (n = 10), using blocked randomization to ensure balance between groups. To enhance the objectivity of outcome assessment, all evaluations will be performed by an assessor who is blinded to group allocation. The experimental group will perform an air stacking-based diaphragmatic breathing exercise using an Ambu-bag, three times per week for 20 minutes over a 4-week period, in addition to neurodevelopmental treatment. The control group will receive therapist-guided diaphragmatic breathing exercises with the same frequency and duration, combined with the same neurodevelopmental treatment program. Both groups will receive the interventions for 4 weeks in the same rehabilitation setting.

All participants will undergo assessments before the start of the intervention and after completion of the 4-week program. Outcome measures will include pulmonary function tests (for example, FVC and FEV1), chest wall expansion, and trunk control ability. In addition, trunk function and functional mobility will be evaluated using the Korean version of the Trunk Impairment Scale (K-TIS) and the Five Times Sit-to-Stand Test (FTSTS), and perceived exertion during exercise will be assessed using the Borg Rating of Perceived Exertion (Borg RPE). Pre- to post-intervention changes will be calculated for each participant, and differences in these changes between the experimental and control groups will be analyzed.

The aim of this study is to determine whether a diaphragmatic breathing exercise using the air stacking technique provides additional benefits over conventional diaphragmatic breathing in improving pulmonary function, chest wall expansion, trunk control, and functional performance in patients with stroke. The findings are expected to demonstrate the therapeutic potential and clinical feasibility of an Ambu-bag-assisted air stacking technique and to contribute to the development of more effective respiratory and trunk rehabilitation strategies for individuals with stroke.

Inclusion Criteria:

• Inpatients diagnosed with stroke (intracerebral hemorrhage or cerebral infarction) at a general hospital in Daegu, currently receiving physical therapy
• Onset of stroke at least 3 months prior to enrollment
• Spasticity grade of 2 or less on the Modified Ashworth Scale
• No congenital deformity or fracture of the thorax or other orthopedic conditions affecting the chest wall
• No history of pulmonary disease before or after the stroke
• Able to perform respiratory exercises as instructed
• Mini-Mental State Examination-Korean version (MMSE-K) score of 24 or higher, indicating sufficient cognitive ability to understand the study procedures
• Presence of decreased pulmonary function (reduced pulmonary function test parameters) at baseline

Exclusion Criteria:

• Acute stroke status or onset of stroke less than 3 months prior to enrollment
• Severe cardiovascular or respiratory disease that makes participation in respiratory exercise unsafe or impossible
• Cognitive impairment or communication disorder that prevents understanding or performing the study procedures
• Any other medical or safety condition judged by the investigator to make participation in the study inappropriate

Outcome assessments will be performed by a physical therapist who is blinded to group allocation.