Effects of Respiratory Muscle Strength Training in Children With Asthma

• Exercise (Other): Inspiratory muscle training will be performed for 8 weeks, 3 days per week, under face-to-face supervision of the researcher using a POWERbreathe Classic Light Resistance device (POWERbreathe International Ltd., Birmingham, UK). Training resistance will initially be set at 40% of the participant's maximal inspiratory pressure (MIP). Participants will perform 30 deep respiratory cycles per session, consisting of three sets of 10 repetitions with 15-minute rest intervals between sets. Training will be performed in a seated position with a nose clip. This intervention will be provided in addition to the thoracic expansion exercise program.
• Exercise (Other): Thoracic expansion exercises will be performed as a home-based program for 8 weeks, 3 days per week. Participants will perform slow, deep nasal inspiration while focusing on lateral and anterior expansion of the chest wall, followed by a 3-5-second breath hold and slow expiration through the mouth. On each exercise day, participants will complete 120 repetitions in three daily sessions (40 repetitions in the morning, 40 at noon, and 40 in the evening). Each 40-repetition session will consist of two sets of 20 repetitions with 1-2 minutes of rest between sets. Participants will send the researchers a video of one exercise session at the end of each exercise day.

Primary outcomes

• Inspiratory Muscle Strength [Baseline and after the 8-week intervention]: nspiratory muscle strength will be assessed by measuring maximal inspiratory pressure (MIP) using a respiratory pressure measurement device (COSMED Pony FX, COSMED Srl, Rome, Italy) in accordance with ATS/ERS recommendations. MIP will be recorded in cmH2O. Measurements will be performed before and after the 8-week intervention.
• Pulmonary Function [Baseline and immediately after the 8-week intervention]: Pulmonary function will be assessed using spirometry. Forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and the FEV1/FVC ratio will be recorded. Peak expiratory flow (PEF) will also be measured using a peak flow meter. Measurements will be performed before and after the 8-week intervention.
• Inspiratory Muscle Endurance [Baseline and after the 8-week intervention]: Inspiratory muscle endurance will be assessed using an incremental threshold loading test with a POWERbreathe Classic Light Resistance device. The test will begin at 20% of the participant's maximal inspiratory pressure (MIP), and the load will be increased by 20% of MIP every 2 minutes up to 100% of MIP. The highest successfully completed pressure will be recorded in cmH2O. Measurements will be performed before and after the 8-week intervention.

Secondary outcomes

• Heart Rate Variability [Baseline and immediately after the 8-week intervention]: Heart rate variability will be assessed using a Polar H10 heart rate sensor (Polar Electro Oy, Kempele, Finland) with Kubios HRV Scientific software. Low-frequency (LF) and high-frequency (HF) components will be obtained, and the LF/HF ratio will be used to assess sympathovagal balance.
• Functional Exercise Capacity [Baseline and immediately after the 8-week intervention]: Functional exercise capacity will be assessed using the 6-Minute Walk Test (6MWT) according to American Thoracic Society recommendations. Participants will walk along a 30-meter course for 6 minutes, and the total distance walked will be recorded in meters. The test will be performed twice with a 15-20-minute rest period between tests, and the greater walking distance will be used for analysis.
• Asthma Control [Baseline and immediately after the 8-week intervention]: Asthma control will be assessed using the Turkish version of the Asthma Control Test (ACT). The ACT consists of 5 items assessing asthma symptoms, their effects on daily activities, and rescue medication use during the previous 4 weeks. The total score ranges from 5 to 25, with higher scores indicating better asthma control. Scores of 19 or lower indicate uncontrolled asthma, while scores of 20 or higher indicate controlled asthma.
• Asthma-Related Quality of Life [Baseline and immediately after the 8-week intervention]: Asthma-related quality of life will be assessed using the Turkish version of the Pediatric Asthma Quality of Life Questionnaire (PAQLQ). The questionnaire consists of 23 items covering three domains: symptoms, activity limitations, and emotional function. Items are scored on a 7-point scale, with higher scores indicating better quality of life.
• Climate Change Anxiety [Baseline and immediately after the 8-week intervention]: Climate change anxiety will be assessed using the Turkish version of the Climate Change Anxiety Scale. The scale consists of 13 items rated on a 5-point Likert scale ranging from 1 (Never) to 5 (Almost Always) and includes cognitive impairment and functional impairment subdomains.

Other outcomes

• Sociodemographic Data [At the beginning of the study]: Age, sex, Height, weight, BMI, Smoking status, economic status, drug treatments, duration of illness

Sex: All, ages: 12 Years to 18 Years

Inclusion Criteria:

* Aged between 12 and 18 years.
* Diagnosed with asthma according to the Global Initiative for Asthma (GINA) criteria.
* Clinically stable asthma.
* No increase in asthma medication dosage within the previous 3 months.

Exclusion Criteria:

* Asthma exacerbation requiring prescription of corticosteroid medication.
* History of thoracic surgery.
* Previous participation in a rehabilitation program.
* Presence of other chronic diseases, including neuromuscular, rheumatologic, cardiovascular, or renal diseases.