Participants
Participants with a diagnosis of mild‐to‐moderate asthma and CF, as well as healthy children and adolescents were selected. General inclusion criteria was children and adolescents aged 7–18 years. General exclusion criteria were: (i) respiratory exacerbations 4 weeks prior to the evaluation, and (ii) presence of musculoskeletal condition or any other disorder that influences exercise capacity. Patients with mild‐to‐moderate asthma were selected consecutively in the outpatient clinics of the Pediatric Pulmonology department (Hospital Universitario Infantil Niño Jesús). Specific inclusion criteria were: (i) asthma diagnosis with at least 6 months of evolution, (ii) exercise‐associated symptoms (score 0–1 in question 2 of the asthma control test (c-ACT)25, or score 2–3 in question 7 of the asthma control in children (CAN) 26. Specific exclusion criteria were: (i) need for increased use of basal medication, inhaled corticosteroid dose, long‐acting β2 agonist, leukotriene receptor antagonists, oral corticosteroids or omalizumab, (ii) respiratory exacerbation requiring systemic corticosteroids in the last 3 months or presence of mild exacerbations in the last month (need for a higher-than-usual dose of short-acting beta-agonist), (iii) irregular use of the medication prescribed by the physician, and (iv) presence of another chronic respiratory or cardiac disease. No medications were withdrawn during the test days and patients kept their usual treatment regimen. Participants with CF were also recruited at Hospital Niño Jesus in Madrid. Specific inclusion criteria was a genetic diagnosis of CF. Specific exclusion criteria were: (i) having severe lung deterioration, as defined by an FEV1 lower than 50% of the predicted, and (ii) presenting unstable clinical condition (i.e., hospitalization within the previous 3 months or exacerbation in the previous 4 weeks). None of the patients included received CF modulator therapy at the moment of evaluation.
Healthy children were recruited from schools in the same district as the hospital to avoid significant differences in environmental conditions (levels of air contamination, presence of environmental allergens, and pollen). Children were selected by convenience sampling, using a covariate adaptive randomization to reduce selection bias. Specific eligibility criteria were: (ii) attending schools in the same district as the hospital, and (ii) having no positive answers in the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire 27. Specific exclusion criteria were the diagnosis of cardiac, neurological, or chronic respiratory diseases that would impair cardiorespiratory fitness.