Supervised home-based respiratory muscle training (RMT) programs improved quality of life, respiratory muscle function, and lower limb strength in individuals with long-term post COVID-19 symptoms, but did not improve their exercise tolerance, lung function, or psychological condition. These are among the study findings published recently in the Annals of Physical and Rehabilitation Medicine.
Researchers’ primary objective was to assess effects of home-based RMT programs (involving both inspiratory and expiratory muscle training) as well as inspiratory muscle training (IMT) programs on quality of life and exercise tolerance among individuals with long-term post-COVID-19 symptoms. Investigators’ secondary goal was to assess these programs for psychological aspects, physical and lung function, and respiratory muscle function.
The researchers conducted a double-blind, parallel 4-arm, randomized controlled trial (ClinicalTrials.gov Identifier: NCT04734561) that included participants recruited from 2 non-profit organizations in Spain supporting individuals with long-term post-COVID-19 symptoms. All participants were adults who experienced fatigue and dyspnea symptoms for at least 3 months following a confirmed SARS-CoV-2 positive reverse-transcription-polymerase chain reaction (RT-PCR) test.
The 88 participants were randomly divided into 4 groups: IMT, IMT-sham, RMT, and RMT-sham. They then underwent 8 weeks of training using a real or sham training device. Physiotherapists and participants knew their training modality (RMT or IMT) but were blinded as to whether they were part of the actual or sham group. The primary endpoints were scores on a quality of life questionnaire (EuroQol-5D) and an exercise tolerance (Ruffier) test. These scores were taken before and after the intervention as well as at week 4. Secondary endpoints included measured levels of depression/anxiety and post-traumatic stress disorder, lung function, physical function, and respiratory muscle function.
In comparing the RMT group vs the RMT-sham group, researchers found the RMT group had a statistically significant health-related quality of life (HRQoL) improvement (d>0.90) post-intervention although no noticeable improvement in exercise tolerance. Notably, no statistically significant difference in quality of life was seen at week 4.
All groups except RMT-sham showed a significantly improved quality of life post-intervention vs baseline. No statistically significant differences in exercise tolerance were found between groups, although exercise tolerance did improve in the RMT group compared with baseline (P =.047).
The respiratory muscle training programme was effective in improving HRQoL, but not exercise tolerance, only when combined inspiratory and expiratory muscle training was performed.
Statistically significant large increases in inspiratory muscle strength and endurance (d≥0.80) and in lower limb muscle strength (d≥0.77) were seen in both the IMT and RMT groups vs their sham counterparts. The RMT group displayed a large, statistically significant increase (d≥0.87) in expiratory muscle strength and peak expiratory flow vs the other 3 groups. The RMT group displayed a 5- to 6-fold increased reduction in dyspnea vs the sham groups (IMT-sham P =.031; RMT-sham P =.008) and the IMT group showed a 5-fold increased reduction in dyspnea vs the RMT-sham group (P =.017). No other statistically significant between-group differences were noted.
Study limitations include underpowered sample size; the lack of conventional cardiopulmonary exercise testing to evaluate exercise tolerance; the inability to calculate intervention effects for varying levels of dyspnea and fatigue; the absence of cardiorespiratory or endurance exercise in the training programs; possible selection bias; and no evaluation of medium or long-term effects of the intervention.
The investigators concluded, “The respiratory muscle training programme was
effective in improving HRQoL, but not exercise tolerance, only when combined inspiratory and expiratory muscle training was performed.” They added that the IMT and RMT programs were “effective in improving respiratory muscle function and lower limb muscle strength, but had no impact on lung function and psychological status.”