This study aimed to evaluate the effect of inspiratory muscle training (IMT) in adults with long COVID and impaired inspiratory muscle strength.
A randomized controlled trial was conducted between September 2021 and December 2023 at Karolinska University Hospital in Sweden. Individuals with long COVID that had impaired inspiratory muscle strength were included and randomized to an IMT or control group.
Both groups performed individualized physical exercise twice weekly for eight weeks. Additionally, the IMT group performed IMT twice daily starting at 20-50 % of their baseline maximal inspiratory pressure (MIP).
Primary outcome was change in inspiratory muscle strength, measured with MIP (percent of predicted value). Secondary outcomes included change in self-rated health (EQ VAS, scale from 0-100), dyspnea (mMRC) and the six-minute walk test (6MWT).
Independent and dependent t-tests were used to analyze between- and within-group differences. The odds of clinically relevant changes in MIP between groups were calculated using Odds Ratio (MCID for long covid: increase in MIP ≥22.1 %).
Per protocol analysis included 32 participants (IMT = 16; Control = 18). At baseline, mean age was 51 years (SD = 13) and 81 % were women. Time from COVID-19 was in median 21 months (IQR = 8.75) and 74 % were not hospitalized during their COVID-19. Mean EQ VAS at baseline was 53 (SD = 22.3), 94 % experienced severe dyspnea (mMRC-score≥2) and mean distance in the 6MWT was 84 % of the predicted value. Median MIP was 48 % (IQR = 24.3) in the intervention group and 51 % (IQR = 14.3) in the control group. There were no significant between-group differences in any of the outcomes at baseline.
Post intervention, there was a significantly higher increase in MIP in the IMT group compared to the control group (U = 84.5, p = .042, rB= .413). MIP increased by in median 28 % (IQR = 38.3) in the IMT group, compared to 11 % (IQR = 13.0) in the control group. A dependent t-test indicated that self-rated health increased significantly within the IMT group from in median 58 (IQR = 31) at baseline to 65 (IQR =15) post-intervention (z = -2.103, p = .036, rB= .294). However, there was no significant between-group differences for any of the secondary outcomes.
The odds of having a clinically relevant increase in MIP were five times higher in the IMT group compared to the control group (95% CI [1.03, 24.28 ], p = .038). In the IMT group, 50 % (8/16) of the participants had a clinically significant increase in MIP, compared to 17 % (3/18) in the control group.
Our findings from a small cohort indicate that IMT may lead to clinically relevant improvements in inspiratory muscle strength in adults with long COVID that have impaired inspiratory muscle strength.
Incorporating IMT into physiotherapy treatment could enhance inspiratory muscle function in this population. Future, larger studies are needed to explore long-term benefits and potential impacts on other health outcomes.
Respiratory muscle function
Inspiratory muscle training
