Effects of inspiratory muscle training on exercise capacity, muscle oxygenation and strength, physical activity, and dyspnea in patients with post-COVID-19 syndrome and pulmonary involvement: a randomized controlled triple-blinded study

Abstract

Background: Coronavirus disease 2019 (COVID-19) affects multiple organ systems, particularly the lungs, where hypoxemia may occur. Musculoskeletal problems, fatigue, and exercise intolerance frequently occur. The effects of inspiratory muscle strength training (IMST) have not been adequately investigated in patients with post-COVID-19. This study aimed to investigate the effects of IMST on functional exercise capacity, muscle oxygenation and strength, fatigue, and dyspnea in patients with post-COVID-19 syndrome and pulmonary involvement. Methods: A randomized controlled, triple-blinded study including 40 patients with post-COVID-19 syndrome and pulmonary involvement. Patients were divided into IMST and control groups. The IMST group performed IMST using a threshold inspiratory muscle trainer (POWERbreathe®, HaB International Ltd., UK) at 50% of MIP, while the control group performed breathing exercises for 7 days/8 weeks. Respiratory muscle strength (mouth pressure device), functional exercise capacity [6-minute walk test (6-MWT)], muscle oxygenation [near infrared spectroscopy (NIRS)], peripheral muscle strength (dynamometer), physical activity (metabolic holter), dyspnea [London Chest Activity of Daily Living Scale (LCADL)], fatigue [(Fatigue Severity Scale (FSS)] were evaluated. Results: After training, 6-MWT distance (Cohen’s d = 0.65), ΔSmO₂ (%), and peripheral muscle strength (Cohen’s d = 0.60–0.73) significantly improved in the IMST group compared to the control group (all p < 0.001). LCADL total score (Cohen’s d = 0.55, p = 0.008) and FSS score (Cohen’s d = 0.73, p < 0.001) also improved, while no significant changes were observed in physical activity levels, including average METs (Cohen’s d = 0.42, p = 0.301). Conclusions: IMST is a practical method for enhancing peripheral muscle strength and oxygenation, functional exercise capacity, alleviating fatigue, and improving impairments associated with long-term hypoxemia in patients with post-COVID-19 syndrome. By focusing on post-COVID-19 with clearly defined pulmonary involvement, this study provides evidence of the isolated physiological effects of IMST, an area that has remained underexplored. These findings support the integration of IMST into pulmonary rehabilitation programs for this specific patient group. Future studies with longer-term follow-up are needed to confirm the sustainability of these effects. Trial registry: Clinical Trials Registry Number: NCT05231395; Registration date: February 9, 2022.