Effect of inspiratory muscle training on inspiratory muscle strength in adults with post-COVID-19 condition and inspiratory muscle weakness: a randomized controlled trial

OBJECTIVE: Evaluate the effect of inspiratory muscle training in adults with post-COVID-19 condition (PCC) and inspiratory muscle weakness. DESIGN: Randomized controlled trial. SUBJECTS/PATIENTS: Adults with PCC and inspiratory muscle weakness. METHODS: Participants were randomized to inspiratory muscle training twice daily plus individualized exercise twice weekly or exercise alone, with weekly follow-ups over 8 weeks. PRIMARY OUTCOME: inspiratory muscle strength (Maximal Inspiratory Pressure). SECONDARY OUTCOMES: expiratory muscle strength (Maximal Expiratory Pressure); functional capacity (Six‑Minute Walk Test; One‑Minute Sit‑to‑Stand); lung function (spirometry); dyspnoea (mMRC); respiratory symptoms (chest tightness, impaired deep breathing, breathing‑related pain); cough frequency (CAAT cough item); fatigue (Fatigue Severity Scale); physical activity (Frändin-Grimby Activity Scale); activity limitations (Patient‑Specific Functional Scale); and health-related quality of life (EQ‑5D‑5L). Intention-to-treat analyses used imputed missing data. Estimated sample size: 90. RESULTS: Forty-four participants were included (median age 47; 82% women; n = 22/group). Between‑group differences favoured the intervention for inspiratory muscle strength (mean difference: 18%; 95% CI: 5-30; OR for clinically meaningful improvement: 7.08, 95% CI: 1.31-38.32) and cough frequency. No other between-group differences were observed. CONCLUSION: Inspiratory muscle training may improve inspiratory muscle strength and reduce cough frequency, but limited sample size and underrepresentation of the most severely affected warrant cautious interpretation.