Diversity of Factors Associated with Physical Inactivity in Patients with Asthma Based on Activity Intensity

Background: The factors contributing to physical inactivity in patients with asthma remain unclear. We aimed to explore the pulmonary and extra-pulmonary factors associated with physical activity (PA) in these patients, with stratification by activity intensity. Methods: Patient demographics, Charlson Comorbidity Index, lung function, bronchial and alveolar nitric oxide (NO) levels, six-minute walk test (6 MWT), and PA were cross-sectionally evaluated in healthy participants (n = 14) and patients with asthma (n = 29). The desaturation-distance ratio (DDR) was measured as an index derived from travel distance and desaturation levels during the 6 MWT. Results: Patients with asthma had significantly lower PA than healthy participants, regardless of activity intensity (≥2 metabolic equivalents [METs]: 198 min vs. 240 min, p < 0.05; ≥3 METs: 54 min vs. 86 min, p < 0.05; ≥4 METs: 10 min vs. 26 min, p < 0.01). Extra-pulmonary factors (age, comorbidities, and 6 MW distance) showed higher correlation coefficients with PA as activity intensity increased. Contrastingly, pulmonary factors (asthma severity, airflow limitation, and alveolar exhaled NO) showed lower correlation coefficients with PA as activity intensity increased. The DDR was negatively associated with active time across all activity intensities. Conclusions: Our findings suggest that aging and comorbidities are potential limiting factors for moderate-to-vigorous physical activity, whereas asthma severity and airway dysfunction restrict daily life in patients with asthma. Moreover, the DDR could facilitate detection of real-life physical inactivity in patients with asthma.