This is single-center cross-sectional mechanistic study in lean and obese children with moderate-severe asthma, followed by a randomized, SHAM-controlled trial of Inspiratory Training (IT). The primary outcome is to describe the contributions of inspiratory muscle dysfunction (IMD) and Small Airway Dysfunction (SAD) to obesity-related versus non-obesity-related asthma. The study will involve training (IT) for 8 weeks at three intensity levels (SHAM, low and high). Target dose: 150 inspirations three times weekly. The population includes 6 to 17-year-old children with moderate to severe asthma and with a body mass index qualifying as normal habitus (BMI 5th to 84th CDC percentile) or obese habitus (≥95th percentile BMI and less than 170% of the 95th CDC percentile). Participants will be involved for 10 weeks. The investigators will use analysis of covariance (ANCOVA) to estimate and test the difference in mean values of baseline measures between obese and non-obese cohorts. Covariates will include age, sex (male/female), race/ethnicity, baseline asthma severity (NAEPP step 2 vs ≥3), and atopy status

Cross-sectional analytic study of pulmonary mechanics comparing lean and obese children with asthma followed by a randomized, SHAM-controlled 3-arm intervention trial of inspiratory training on small airway dysfunction and inspiratory muscle function.

The central objective of the MICA (Mechanistic Study of Inspiratory Training in Childhood Asthma) study is to assess key respiratory mechanisms in 6-17 year olds with symptomatic asthma (with and without obesity) in response to IT. Our central hypothesis is that obesity promotes dyspnea and worse asthma control via inspiratory muscle fatigue/dysfunction (IMD) and small airway dysfunction (SAD), and that IT will improve inspiratory muscle function and small airway measures.

The sample size calculations and main analyses for the IT trial are designed as a traditional parallel arm intervention trial (any dose IT vs. SHAM control) with visits 1-2 serving as the baseline evaluation and the main IT endpoints being collected at the 8-week visit.

In depth phenotyping involving measures of respiratory mechanics and muscle functioning and a RCT involving inspiratory training will address these objectives.

Inclusion Criteria:

• 6-17 years of age
• Documented clinician-diagnosed asthma
• Currently requiring 2 or more controller prescriptions to treat disease (i.e. moderate to severe persistent disease)
• Either obese (≥95th percentile BMI and less than 170% of the 95th CDC percentile) or have a normal BMI (BMI 5th to 84th CDC percentile)

Exclusion Criteria:

• ACT (asthma control test) score <17
• Ever intubated for asthma
• FEV1 < 50% of predicted at enrollment
• Currently pregnant
• Legal guardian unable to consent in English or Spanish
• Any major chronic illness that, in the opinion of the PI, would interfere with participation
• Younger than 6 years of age

For every 1 participant allocated to sham, 2 will be active IT. Among them, half will be allocated low-dose and half high dose. To provide balance among treatment groups regarding sex/obesity-status, randomization will occur within four strata (males obese,females obese,males non-obese,females non-obese).Treatment assignment will be obtained using Duke REDCap enrollment/randomization system. All study staff and participants will be blinded to the treatment assignment at screening/enrollment and prior to treatment group allocation. Participants in the active IT and sham arms will use the same device. Participants may try to discern their device resistance. Although true masking of active IT versus sham may not be possible in all cases, participants will only be told that they are receiving 1 of 3 possible resistances. However, staff members who are assessing endpoints and performing statistical analyses will be blinded to treatment assignment until after the database is locked