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Article

Respiratory Rehabilitation After COVID-19: Efficacy of Inspiratory Muscle Training on Lung Function, Quality of Life and Sleep Quality: A Randomized Clinical Trial

by
Jose Carlos Nóbrega Júnior
1,
Daniella Brandão
1,
Daiara Xavier
1,
Roberta Torres
1,
Simone Soares Brandão
2,
Magno Formiga
3,
James B. Fink
4,
Arzu Ari
4,
Shirley Campos
1 and
Armèle Dornelas de Andrade
1,*
1
Department of Physical Therapy, Federal University of Pernambuco, Recife 50740, Pernambuco, Brazil
2
Department of Nuclear Medicine, Federal University of Pernambuco, Recife 50740, Pernambuco, Brazil
3
Department of Physical Therapy, Federal University of Ceará, Fortaleza 60440, Ceará, Brazil
4
Department of Respiratory Care, Texas State University, Round Rock, TX 78665, USA
*
Author to whom correspondence should be addressed.
COVID 2026, 6(1), 22; https://doi.org/10.3390/covid6010022
Submission received: 18 December 2025 / Revised: 29 December 2025 / Accepted: 9 January 2026 / Published: 19 January 2026
(This article belongs to the Section COVID Public Health and Epidemiology)
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Abstract

Background and Purpose: Post-COVID-19 syndrome significantly impacts respiratory function and quality of life. Inspiratory muscle training (IMT) has been proposed as a potential intervention to improve respiratory muscle strength and overall recovery. This study aimed to evaluate the effects of IMT on respiratory muscle performance, lung function, functional capacity, sleep quality, and quality of life in individuals with post-COVID-19 syndrome. Methods: Nineteen individuals with post-COVID-19 syndrome were randomized into an IMT group (N = 10) or a sham group (N = 9). The IMT group performed eight weeks of training at 50% of maximal inspiratory pressure (MIP), while the sham group used a non-load device. Outcomes included MIP (cm H2O), functional capacity (6MWT), lung function (spirometry), sleep quality (PSQI), and quality of life (SF-36). Results: The IMT group showed significant improvements in MIP (125.50 ± 22.50 vs. 93.67 ± 20.87 cm H2O; p = 0.036; Cohen’s d = 0.50), PSQI (4.40 ± 2.50 vs. 9.00 ± 2.80; p = 0.011; Cohen’s d = 0.60), and SF-36 (p = 0.030). The IMT group also increased 6MWT distance by 58.36 ± 25.10 m. Conclusions: IMT significantly improved respiratory muscle strength, sleep quality, and quality of life in post-COVID-19 syndrome. These findings suggest that IMT may be an effective intervention, warranting further studies to confirm long-term benefits.

Graphical Abstract

1. Introduction

Post-COVID-19 syndrome is characterized by the persistence of multiple symptoms for weeks or months after acute SARS-CoV-2 infection, which may impair the pulmonary, cardiovascular, nervous, and metabolic systems [1]. Common symptoms include persistent fatigue, dyspnea, chest pain, palpitations, cognitive disorders, headache, sleep disturbances, anxiety, and depression. Several mechanisms have been proposed to explain the multifactorial etiology of post-COVID-19 syndrome, including persistent immunologic dysfunction, chronic low-grade inflammation, endothelial dysfunction, neuroinvasive effects, and direct or indirect tissue damage. Genetic predisposition, preexisting comorbidities, and environmental factors may also increase susceptibility to and severity of post-COVID-19 syndrome [2].
Previous studies have demonstrated that individuals who have recovered from COVID-19 often experience impairments in lung function and diffusion capacity, resulting in reduced functional capacity. In addition, neuromuscular and inflammatory alterations induced by viral infection may cause insomnia, sleep apnea, and daytime fatigue, thereby affecting sleep quality. These conditions reduce lung function and quality of life, hindering daily activities and psychological well-being [1,3]. However, the mechanisms underlying chronic symptoms and the efficacy of different interventions remain unclear.
In this context, inspiratory muscle training (IMT) may improve lung function and functional capacity in various clinical conditions. This training increases the strength and endurance of respiratory muscles, reduces dyspnea, and improves functional capacity and quality of life [4]. However, the benefits of IMT for individuals with post-COVID-19 syndrome remain unclear because existing studies show divergence in several factors (e.g., heterogeneity of protocols, inclusion of individuals without a diagnosis confirmed by reverse transcription polymerase chain reaction [RT-PCR], and combination of IMT with other exercise modalities), which limits adequate comparison. Therefore, this study aimed to analyze respiratory muscle performance, lung function, functional capacity, sleep quality, and quality of life in individuals with post-COVID-19 syndrome before and after an eight-week IMT program.

2. Materials and Methods

This randomized, double-blind clinical trial involved individuals with post-COVID-19 syndrome. Convenience sampling included individuals attending major referral centers due to the persistence of post-infection symptoms; invitations were extended through direct outreach or social media.
The study was approved by the Human Research Ethics Committee under protocol no. 4.983.173 and was registered at ClinicalTrials.gov (ID: NCT05282199). All participants were informed about the study and provided written informed consent obtained by the responsible researcher.
After the initial evaluation, a third person not directly involved in the study categorized participants into blocks of four using a table of random numbers to ensure allocation concealment. Only the research team member responsible for load adjustment was aware of group assignment.
Individuals of both sexes, aged ≥ 18 years, who were not engaged in any form of physical activity and had been diagnosed with COVID-19 after the acute phase of infection, with the first infection confirmed by reverse transcription polymerase chain reaction (RT-PCR) testing, were included. Individuals reporting disorders prior to COVID-19 (i.e., orthopedic, neurologic, uncontrolled cardiovascular, or pulmonary disease), pregnancy, or being in the active infection phase were excluded.
Participants were categorized according to the severity of post-COVID-19 syndrome based on the severity, intensity, and persistence of symptoms following acute infection. The score was calculated from self-reported symptoms using a questionnaire composed of 12 symptom sets, including chemosensory deficits, fatigue, exercise intolerance, joint or muscle pain, ear–nose–throat conditions, cough or wheezing, chest pain, gastrointestinal disorders, neurological conditions, dermatological diseases, signs of infection, and sleep disturbances. If any symptom within these sets was present, the indicators were multiplied by an individual point value representing their contribution to PCS severity. The sum of the assigned points yielded a total score, allowing classification of PCS severity into the following categories: none (0 points), mild (>0 to ≤10.75), moderate (>10.75 to ≤26.25), and severe (>26.25) [5].
Regarding outcome assessment, all data analyses were conducted under blinded conditions. Group identifiers were fully anonymized before analysis, and investigators responsible for processing and analyzing study outcomes had no access to information regarding participants’ allocation to the IMT or sham groups. This blinding procedure applied to all outcome variables, including respiratory muscle performance, functional capacity, quality of life, and sleep-related measures. Specifically, the analyst responsible for sleep data processing and analysis remained unaware of group assignment throughout the entire analytical process. These procedures were implemented to ensure methodological rigor, minimize the risk of analytical bias, and enhance the reliability, validity, and safety of the collected data.

2.1. Instruments for Data Collection

2.1.1. Inspiratory Muscle Performance

The assessment of inspiratory muscle performance was conducted before, weekly during, and after the intervention using the test of incremental respiratory endurance (TIRE) [6] and the PrO2 device (PrO2Fit Health, Smithfield, RI, USA), a portable, wireless manometer paired with a smartphone application that provided graphical biofeedback during the maneuvers. The TIRE provided measures of maximal inspiratory pressure (MIP), sustained maximal inspiratory pressure (SMIP), and inspiratory duration (ID). All maneuvers were performed in accordance with the European Respiratory Society (ERS) recommendations for respiratory muscle testing [7].

2.1.2. Lung Function

Lung function was assessed using the digital spirometer KoKo® (nSpire Health, London, UK). The tests were performed before and after the intervention in accordance with the American Thoracic Society (ATS) lung function guidelines [8]. Forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), and the ratio of FEV1 to forced vital capacity (FEV1/FVC) were expressed as percentages of predicted values for the Brazilian population, according to Pereira et al. (2007) [9].

2.1.3. Functional Capacity

The six-minute walk test (6MWT) was performed before and after the intervention in accordance with American Thoracic Society (ATS) recommendations [10]. Participants were instructed to walk as fast as possible along a 30 m corridor for six minutes. The distance covered was expressed as absolute values and as percentages of predicted values for the Brazilian population, according to the equation proposed by Britto et al. (2014) [11].

2.1.4. Sleep Parameters

The objective assessment of sleep was performed before and after the intervention using the Actigraph Actrust 2 (Copyright © 2014, Condor Instruments Ltd., São Paulo, Brazil). Participants were instructed to wear the device for seven consecutive days on the non-dominant upper limb during their usual sleep and wake periods; they were allowed to choose their sleep and wake times during this period. Data were retrieved during the second laboratory visit after seven days. The assessments comprised sleep efficiency (ratio of total sleep time to total time in bed), sleep onset latency (time in minutes between bedtime and sleep onset), wake after sleep onset (number of minutes recorded as awake during the sleep period after sleep onset), and total sleep time (duration of sleep during the longest nocturnal sleep period). Sleep diaries, when completed by participants, were used to indicate sleep schedule times [12].
Assessment of Daytime Excessive Sleepiness
The Epworth Daytime Sleepiness Scale (EDSS) was administered before and after the intervention. The EDSS is a validated instrument for the Brazilian population that assesses common daily situations, allowing self-assessment of the likelihood of falling asleep during these activities. The maximum total score is 24 points; values ≥ 10 indicate excessive daytime sleepiness requiring further investigation [13].
Sleep Quality Assessment
The Pittsburgh Sleep Quality Index (PSQI) was used to assess sleep quality before and after the intervention. This tool includes seven components with 19 items. The overall score is the sum of scores of the seven components, categorizing the sleep quality as good (0 to 4 points) or poor (>5 points) [14].
Quality of Life Assessment
The quality of life was assessed before and after the intervention using the 36-Item Short-Form Health Survey (SF-36). The final score ranged from zero to 100, in which zero and 100 corresponded to the worst or best global health statuses, respectively [15].

2.2. Intervention

Participants underwent moderate-load inspiratory muscle training, defined as 50% of their maximal inspiratory pressure (MIP), with weekly adjustments during in-person laboratory visits over an 8-week period. Training was performed using the PowerBreathe® Classic Light device (POWERbreathe® Classic, POWERbreathe International Ltd., Southam, UK), which was calibrated according to the manufacturer’s specifications before the intervention to ensure accurate and consistent resistance levels. In the sham group, the internal spring of the device was removed, ensuring no resistance to inspiratory flow throughout the eight-week period.
Training sessions were conducted in a seated position, with knees and ankles flexed at 90°, feet flat on the floor, one hand holding the device and the other resting on the leg. A nasal clip was used to prevent air leakage. The IMT protocol consisted of three cycles of 30 maximal and rapid inhalations performed against a predefined resistance using a threshold-loading device, with a one-minute rest interval between cycles. Participants were instructed to perform the sessions twice daily, seven days per week, over the 8-week period. Each inspiratory effort was executed from functional residual capacity (FRC) to total lung capacity (TLC) as explosively and vigorously as possible, with emphasis on speed and maximal effort, aiming to recruit fast-twitch inspiratory muscle fibers.
Adherence to the inspiratory muscle training protocol was monitored using a combination of self-reported and objective verification methods. In addition to training diaries completed by participants, adherence was verified during weekly in-person visits, during which MIP was reassessed to monitor physiological progression and confirm engagement with the training protocol. These visits also allowed direct verification of training execution and adjustment of training load when necessary. Furthermore, the researcher maintained regular contact with participants throughout the intervention period via telephone calls and messages, facilitating continuous follow-up, reinforcing adherence, and confirming that training sessions were performed as prescribed. Adherence was considered satisfactory when participants completed at least 80% of the prescribed sessions over the 8-week period.
Inspiratory muscle strength was reassessed weekly using MIP measurements, and the training load was adjusted accordingly, typically recalibrated to 50% of the newly measured MIP to ensure progressive overload and individualized training intensity. After the training period, all participants were reassessed using the same instruments and protocols applied during the initial assessment. All evaluations were conducted by the same evaluator to ensure intra-rater reliability and consistency in data collection.

2.3. Sample Size

The sample size calculation was performed using an a priori analysis with G*Power version 3.1.9.7, based on a previous study conducted by our team that investigated the effects of inspiratory muscle training (IMT) in a distinct population [16]. This theoretical model was selected due to the lack of available data on the effects of IMT in individuals with persistent post-COVID-19 symptoms at the time the sample size calculation was defined. The training protocol used in the previous study was similar to that used in the present trial, justifying its adoption as the reference for the sample size calculation. The analysis considered the means and standard deviations of maximal inspiratory pressure (MIP) observed in the previous study. To ensure robust detection of effects, a significance level of 5% (α error) and a statistical power of 90% (β error = 10%) were adopted, in accordance with standard statistical guidelines. Considering an anticipated dropout rate of 15%, the final sample size was adjusted to a minimum of 18 participants, with 9 participants per group.

2.4. Statistical Analysis

Data analysis was conducted using SPSS® version 20 (IBM Corp., Armonk, NY, USA). Baseline characteristics and outcome measures were expressed as mean ± standard deviation. Normality and homogeneity of variance were assessed using the Shapiro–Wilk and Levene tests, respectively. Between-group comparisons of baseline characteristics, inspiratory muscle performance, lung function, functional capacity, and sleep parameters were performed using independent-samples t tests. Quality of life was analyzed using a mixed linear model implemented in the lme4 package (R Core Team, 2016, Vienna, Austria), including fixed effects for time (pre- and post-intervention), group (IMT vs. sham), and their interaction. Baseline quality-of-life scores were included as a covariate to adjust for initial between-group differences. Statistical significance was determined using F tests, with p < 0.05 considered statistically significant. Effect sizes were calculated using Cohen’s d and classified as very small (0.1), small (0.2), medium (0.5), or large (0.8) [17].

3. Results

A total of 19 individuals were screened for study participation. The mean age was 43.60 ± 12.84 years in the IMT group and 57.11 ± 15.66 years in the sham group. Severe symptoms were identified in 40.0% of individuals in the IMT group and in 33.3% of those in the sham group, and 26.3% of the total sample required hospitalization in the intensive care unit during the active phase of COVID-19. Figure 1 illustrates the flowchart detailing participant recruitment, randomization, and group allocation.
The baseline characteristics of the sample are shown in Table 1.
Changes in MIP were significantly higher in the TMI group than in the sham group (mean difference: 31.83 cm H2O; 95% CI: 2.43 to 61.32; p = 0.036, Cohen’s d = 0.50). Subjective sleep quality (PSQI) was significantly higher in the TMI group (mean difference: −4.60; 95% CI: −7.99 to −1.20; p = 0.011, Cohen’s d = 0.60). Although the changes in the distance walked and percentage values of the distance walked demonstrated a moderate effect size after the intervention (mean difference: 58.36 m; 95% CI: −13.08 to 129.81; p = 0.103, Cohen’s d = 0.40, and (mean difference: 10.23%; 95% CI: −0.37 to 20.84; p = 0.058, Cohen’s d = 0.50, respectively), values were not significantly different between groups. Changes in sleep efficiency (actigraphy) showed significant differences between the groups (mean difference: 8.42; 95% CI: (2.97 to 13.88); p = 0.005, Cohen’s d = 0.60). The values of all parameters and their differences are shown in Table 2.
The IMT group showed statistically significant improvements compared to the sham group in MIP (125.50 vs. 93.67 cm H2O, p = 0.036 Cohen’s d = 0.50), sleep efficacy (90.48 vs. 82.06%, p = 0.005; Cohen’s d = 0.62), and PSQI scores (4.40 vs. 9.0, p = 0.011; Cohen’s d = 0.60), as shown in Table 2.
Figure 2 shows the variations in the total SF-36 score over time between groups. The analysis revealed a significant interaction between time and group (p = 0.030), indicating that the impact of the intervention on quality of life was statistically different between groups.
The incidence of adverse effects related to IMT was low in both groups. In the IMT group, a small proportion of participants reported transient dizziness (8%) or mild muscle pain (12%), none of which required interruption of the protocol. In the sham group, which trained without incremental load, discomfort was even less frequent and was limited to isolated cases of mild fatigue (4%). These findings reinforce the safety of IMT when conducted under appropriate supervision and with individualized progression.

4. Discussion

This study investigated the effects of an eight-week IMT program in individuals with post-COVID-19 syndrome. Despite the infection having occurred a prolonged time ago, on average more than 35 months prior, participants continued to exhibit persistent symptoms, including reduced respiratory muscle strength, low exercise tolerance, sleep disturbances, and impaired quality of life. Following the intervention, IMT led to improvements in these outcomes, suggesting that even in individuals with chronic post-COVID-19 symptoms, IMT may be an effective strategy to alleviate the functional and subjective impairments associated with post-COVID-19 syndrome.
In the present study, maximal inspiratory pressure increased in the IMT group following the intervention. This finding is consistent with the results reported by McNarry et al. (2022) [4], who also observed improved respiratory muscle performance after an eight-week IMT program in patients with post-COVID-19 syndrome. These improvements may be related to a reduction in respiratory neural drive and improvements in breathing patterns, thereby minimizing existing imbalances between the imposed load and the respiratory muscles’ capacity to perform work [18].
Regarding lung function, the results of the present study indicated that lung function was within the normal range. Follow-up studies involving patients with post-COVID-19 syndrome have reported normal or near-normal spirometric values approximately four months after recovery from the acute phase of COVID-19 [19,20]. In addition, lung function did not differ between groups after the intervention.
At baseline, both the IMT and sham groups exhibited reduced sleep efficiency and a high number of nocturnal awakenings. In addition, elevated PSQI scores and excessive daytime sleepiness scale scores indicated poor sleep quality and excessive daytime sleepiness. Considering that nocturnal awakenings disrupt sleep and reduce sleep efficiency, impaired sleep quality contributes to daytime dysfunction, among which mental disorders negatively affect quality of life [21]. In this context, Tanriverdi et al. (2022) [22] reported poor sleep quality and the presence of mid-term chronic symptoms, such as anxiety and depression, in individuals with post-COVID-19 syndrome, thereby supporting the present findings.
Furthermore, Semyachkina-Glushkovskaya et al. (2022) [23] described an increasing prevalence of sleep disorders related to COVID-19, a phenomenon known as coronasomnia, which may disrupt the blood–brain barrier and expose the central nervous system to viruses, including SARS-CoV-2, bacteria, and other toxins. The immune system, activated after viral infection, secretes inflammatory mediators that trigger hyperinflammatory states in the central nervous system to eliminate pathogens. The intensity of the inflammatory response is directly associated with the severity of COVID-19, with more severe cases linked to greater disruption of the blood–brain barrier. Most individuals in the present study had experienced moderate or severe COVID-19, which may help explain the poorer outcomes observed in sleep efficiency, number of nocturnal awakenings, excessive daytime sleepiness, and overall quality of life.
Regarding IMT, the IMT group demonstrated improved sleep efficiency as well as reduced PSQI scores. Azeredo et al. (2022) [24] conducted a randomized clinical trial involving patients with obstructive sleep apnea and reported reductions in PSQI and EDSS scores after a 12-week IMT program performed at intensities ranging from 40 percent to 70 percent of the assessed maximal inspiratory pressure. Another study conducted in middle-aged and older adults investigated the effects of a 12-week physical training program on sleep-related parameters. The results showed improved sleep efficiency and reduced sleep latency in the exercise group compared with the sham group; however, total sleep time and the number of nocturnal awakenings did not change after the intervention [25].
This lack of change may be partly explained by the specific characteristics of the studied population. Unlike previous studies that included individuals with obstructive sleep apnea or older adults, the present sample consisted of individuals with post-COVID-19 syndrome and persistent symptoms, even after an average of nearly three years since infection. These individuals exhibited elevated baseline scores for daytime sleepiness and poor sleep quality, as assessed by EDSS and PSQI, indicating chronic alterations in sleep architecture. Additionally, the high number of nocturnal awakenings observed at baseline may suggest a more fragmented and less responsive sleep pattern, which may not be fully addressed by IMT alone.
Additionally, functional capacity in the IMT group improved, as evidenced by a 58.36 m increase in six-minute walk distance after the intervention compared with the sham group. This difference exceeds the minimum clinically important difference established for patients with chronic respiratory diseases [26]. These findings suggest that an eight-week IMT protocol with moderate load may improve functional capacity in individuals with post-COVID-19 syndrome. Consistent with these results, previous studies have also reported improvements in the functional capacity of individuals with post-COVID-19 syndrome following other IMT protocols [27]. The improvement in exercise tolerance and the consequent increase in walking distance after IMT may be related to modulation of the respiratory metaboreflex. This reflex is triggered by respiratory muscle fatigue and results in increased sympathetic activity, peripheral vasoconstriction, and redistribution of blood flow in favor of the respiratory muscles at the expense of locomotor muscles. IMT may attenuate or delay activation of the respiratory metaboreflex, thereby promoting better perfusion of active skeletal muscles during exercise. As a result, peripheral muscle oxygenation improves, leading to increased tolerance to physical exercise [28].
Individuals in both the IMT and sham groups presented low total SF-36 scores. This finding is consistent with the study by Aiyegbusi et al. (2021) [29], which suggests that patients with post-COVID-19 syndrome experience significant reductions in quality of life. In addition, the systematic review conducted by Ahmed et al. (2020) [30] reported lower SF-36 scores in patients who had recovered from COVID-19 compared with healthy individuals. Furthermore, the present study demonstrated improved overall SF-36 scores in the IMT group after the intervention. These improvements observed using the SF-36 may be related to increased respiratory muscle performance and functional capacity, potentially leading to enhanced quality of life in this population.
Despite its valuable contribution to understanding the effects of IMT in post-COVID-19 syndrome, a limitation of the present study is the relatively small sample size. However, it should be emphasized that an a priori sample size calculation was performed based on maximal inspiratory pressure, which was defined as the primary outcome. This calculation was derived from effect estimates reported in a previous study that used a similar inspiratory muscle training protocol and involved a population with comparable characteristics. Assuming a significance level of 5%, a statistical power of 90%, and a dropout rate of 15%, the minimum required sample size was estimated at 18 participants, which was achieved in the present trial. Despite meeting the predefined sample size requirements for the primary outcome, the limited number of participants increases the risk of Type II error, particularly for secondary outcomes such as lung function and functional capacity. Nevertheless, given the wide range of long-term alterations associated with SARS-CoV-2 and the existing gaps in knowledge, these findings provide relevant insights to guide future research and inform intervention strategies.
Several secondary outcomes demonstrated moderate effect sizes without reaching statistical significance. In the context of a small sample, these findings should not be interpreted as evidence of absence of an intervention effect, but rather as potentially reflecting insufficient statistical power to detect true between-group differences. This consideration is particularly relevant for lung function and functional capacity outcomes, for which moderate effect sizes were observed.
Some baseline differences between groups were observed for age, maximal inspiratory pressure, and EDSS scores. Although these differences did not reach statistical significance, they should be interpreted with caution in the context of a relatively small sample. Variations in baseline characteristics, such as age and inspiratory muscle strength, may contribute to individual variability in training response and recovery patterns. Therefore, these baseline differences are acknowledged as a contextual factor when interpreting between-group comparisons and the magnitude of the observed effects.
The eight-week IMT protocol with a moderate load proved to be an effective intervention for individuals with post-COVID-19 syndrome, enhancing respiratory muscle performance, functional capacity, sleep quality, and quality of life. Moreover, IMT is a low-cost, feasible intervention that can be performed at home, facilitating adherence and integration into daily routines.
From a clinical perspective, inspiratory muscle training represents a low-cost, safe, and easily applicable intervention that can be implemented in home-based rehabilitation programs. Its minimal equipment requirements and favorable adherence profile make IMT particularly suitable for resource-limited settings and for individuals with restricted access to supervised rehabilitation services, potentially expanding rehabilitation opportunities for patients with post-COVID-19 syndrome.
Future studies should investigate IMT effects in stratified samples according to COVID-19 severity and explore the influence of training parameters (e.g., duration, intensity, frequency) on physiological adaptations to optimize IMT prescription for this population.

5. Conclusions

This study demonstrated that an eight-week IMT protocol increased respiratory muscle strength, improved functional capacity, and enhanced quality of life in individuals recovering from post-COVID-19 syndrome. Notably, the IMT group also exhibited substantial improvements in sleep quality, as evidenced by both objective and subjective measures. These findings suggest that IMT may be beneficial for this population and represent a valuable supplementary treatment option.

Author Contributions

J.C.N.J.: Methodology, conceptualization, investigation, data curation, formal analysis, writing—original draft. A.D.d.A.: Writing—review and editing, resources, methodology, investigation, supervision, conceptualization. S.S.B.: Writing—review and editing, resources, supervision, investigation. J.B.F.: Writing—review and editing, conceptualization. D.X.: Writing—investigation, data curation, methodology, conceptualization. R.T.: Writing—investigation, data curation, methodology, conceptualization. A.A.: Writing—review and editing, conceptualization. M.F.: Writing—review and editing, resources, methodology, conceptualization. S.C.: Writing—review and editing, visualization, supervision, resources, methodology, investigation, conceptualization. D.B.: Writing—review and editing, visualization, supervision, resources, methodology, investigation, conceptualization. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Council for Scientific and Technological Development (CNPq, Brazil) under Grant numbers 421756/2021-7, 403341/2020-5, 312587/2022-8, and 445567/2023-6; by the Coordination for the Improvement of Higher Education Personnel (CAPES, Brazil) under Finance Code 001; and by the Foundation for the Support of Science and Technology of the State of Pernambuco (FACEPE, Brazil) under Grant numbers APQ-306240/2021-1, APQ-0801-4.08/21, and APQ-0249-4.08/20.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki and approved by the Human Research Ethics Committee of Universidade Federal de Pernambuco under protocol No. 4.983.173 and registered at clinicaltrials.gov (ID: NCT05282199), 21 September 2021.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author, J.C.N.J., upon reasonable request.

Acknowledgments

We dedicate this work to the memory of Anna Myrna Jaguaribe de Lima, our co-supervisor, whose guidance, commitment, and invaluable contributions were essential to the completion of this study. This acknowledgment is made with the consent of her family.

Conflicts of Interest

Dr. Fink is the Chief Scientific Officer (CSO) of Aerogen Pharm. Dr. Ari discloses her relationships with the COPD Foundation, Aerogen Ltd., Fisher & Paykel Healthcare and the US Department of Labor. The remaining authors declare no conflicts of interest related to this study.

Abbreviations

The following abbreviations are used in this manuscript:
IMTInspiratory Muscle Training
MIPMaximum Inspiratory Pressure
SMIPSustained Maximal Inspiratory Pressure
6MWTSix-Minute Walk Test
FEV1Forced Expiratory Volume in 1 Second
FVCForced Vital Capacity
PSQIPittsburgh Sleep Quality Index
SF-3636-Item Short Form Health Survey
EDSSEpworth Daytime Sleepiness Scale
TIRETest of Incremental Respiratory Endurance
RT-PCRReverse Transcription Polymerase Chain Reaction
BMIBody Mass Index
FRCFunctional Residual Capacity
TLCTotal Lung Capacity
ATSAmerican Thoracic Society
ERSEuropean Respiratory Society

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Figure 1. Study flowchart.
Figure 1. Study flowchart.
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Figure 2. Changes in total SF-36 score from baseline (Before) to post-intervention (After) in the IMT and sham groups. Data points represent group means, and vertical error bars indicate standard deviations (SD). Interaction betwen groups and time are marked with asterisks (*).
Figure 2. Changes in total SF-36 score from baseline (Before) to post-intervention (After) in the IMT and sham groups. Data points represent group means, and vertical error bars indicate standard deviations (SD). Interaction betwen groups and time are marked with asterisks (*).
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Table 1. Baseline Characteristics of Participants in IMT and Sham Groups.
Table 1. Baseline Characteristics of Participants in IMT and Sham Groups.
VariablesIMT Group
(N = 10)		Sham Group
(N = 9)		p-Value
Age (years)43.60 ± 12.8457.11 ± 15.660.079
Weight (kg)82.37 ± 14.1079.80 ± 150.604
Height (m)1.61 ± 0.041.69 ± 0.120.182
BMI (kg/m2)31.73 ± 6.1027.67 ± 2.740.156
Post-COVID-19 period (months)35.63 ± 1.3535.46 ± 0.390.723
Lung function (% predicted)   
FEV174.00 ± 16.2279.00 ± 20.350.560
FVC89.70 ± 14.1289.22 ± 14.720.943
FEV1/FVC84.00 ± 20.3688.55 ± 15.810.596
Inspiratory muscle performance   
MIP (cm H2O)68.10 ± 24.3891.22 ± 34.370.106
SMIP (PTU)463.60 ± 157.21504.33 ± 264.890.685
ID(s)10.50 ± 3.2510.72 ± 2.960.879
Functional capacity   
6MWD (m)463.30 ± 74.32503.00 ± 73.900.260
6MWD %pred84.99 ± 9.6993.02 ± 14.430.169
Sleep parameters   
Time in bed (h)8.32 ± 1.617.14 ± 1.320.103
Total sleep time (h)6.82 ± 1.605.99 ± 1.150.217
Latency (min)3.17 ± 1.972.65 ± 1.510.529
Efficacy (%)83.75 ± 4.3582.63 ± 6.830.672
Night awakenings10.43 ± 3.338.51 ± 2.930.201
EDSS11.40 ± 4.088.67 ± 7.220.318
PSQI9.70 ± 2.4010.33 ± 4.300.693
Symptoms   
Fatigue8 (80%)6 (66.6%) 
Cough, wheezing7 (70%)5 (55.5%) 
Neurological ailments6 (60%)7 (77.7%) 
Joint and muscle pain7 (70%)6 (66.6%) 
Gastrointestinal ailments5 (50%)4 (44.4%) 
Sleeping disturbance8 (80%)8 (88.8%) 
Exercise intolerance6 (60%)7 (77.7%) 
Infection signs0 (0%)1 (11.1%) 
Chemosensory deficits7 (70%)8 (88.8%) 
Chest pain5 (50%)7 (77.7%) 
Dermatological ailments9 (90%)9 (100%) 
Ear-Nose-Throat ailments3 (30%)1 (11.1%) 
Medications   
Corticosteroids3 (30%)2 (22.2%) 
Beta-blocker4 (40%)1 (11.1%) 
Sedatives2 (20%)1 (11.1%) 
Oral antidiabetic2 (20%)1 (11.1%) 
Antidepressants3 (30%)3 (33.3%) 
Note: BMI = body mass index; cm H2O = centimeters of water; FEV1 = forced expiratory volume in the first second; FVC = forced vital capacity; FEV1/FVC: expiratory volume in the first second to forced vital capacity ratio; MIP = maximum inspiratory pressure; ID: inspiratory duration; SMIP: sustained maximal inspiratory pressure. 6MWD: six-minute walking distance; EDSS: Epworth Daytime Sleepiness Scale; PSQI: Pittsburgh Sleep Quality Index. Intergroup comparisons (between groups) were performed using the independent t-test. The significance level adopted was p < 0.05.
Table 2. Means, standard deviations, and mean differences in lung function, respiratory muscle performance, functional capacity, and sleep parameters between IMT and sham groups post-intervention.
Table 2. Means, standard deviations, and mean differences in lung function, respiratory muscle performance, functional capacity, and sleep parameters between IMT and sham groups post-intervention.
VariablesIMT Group N = 10 (Mean ± SD)Sham Group N = 9 (Mean ± SD)Differences in the Means (95% CI)p-ValueEffect Size (Cohen’s d)
Lung Function (% predicted)     
FEV193.50 ± 21.7378.55 ± 20.1814.94 (−5.43; 35.32)0.1400.40
FVC97.20 ± 17.1593.33 ± 15.033.86 (−11.82; 19.56)0.6100.12
FEV1/FVC96.60 ± 15.0986.11 ± 12.4010.48 (−2.97; 23.95)0.1190.40
Respiratory muscle performance     
MIP (cm H2O)125.50 ± 27.6893.67 ± 33.2231.83 (2.43; 61.32) 0.036 * 0.50
SMIP (PTU)657.90 ± 147.52554.78 ± 328.32103.12 (−138.74; 344.98)0.3810.21
ID(s)12.10 ± 1.8511.27 ± 3.500.82 (−1.84; 3.49)0.5250.15
Functional capacity     
6MWD (m)551.70 ± 69.25493.33 ± 78.4158.36 (−13.08; 129.81)0.1030.40
6MWD %pred101.31 ± 6.4091.07 ± 14.4310.23 (−0.37; 20.84)0.0580.50
Sleep parameters     
Time in bed (h)7.35 ± 1.117.59 ± 2.57−0.24 (−2.13; 1.64)0.7870.06
Total sleep time (h)6.53 ± 1.076.53 ± 2.400.01 (−1.76; 1.77)0.9970.01
Latency (min)1.49 ± 0.962.28 ± 1.46−0.78 (−1.97; 0.39)0.1790.32
Efficacy (%)90.48 ± 5.8682.06 ± 5.348.42 (2.97; 13.88)0.005 *0.62
Night awakenings6.61 ± 2.468.54 ± 2.58−1.93 (−4.38; 0.51)0.1130.40
EDSS6.00 ± 4.0010.78 ± 6.62−4.77 (−10.01; 0.45)0.0710.42
PSQI4.40 ± 3.139.00 ± 3.87−4.60 (−7.99; −1.20)0.011 *0.60
Note: FEV1 = forced expiratory volume in the first second; FVC = forced vital capacity; FEV1/FVC: expiratory volume in the first second to forced vital capacity ratio; MIP = maximum inspiratory pressure; ID: inspiratory duration; SMIP: sustained maximal inspiratory pressure. 6MWD: six-minute walking distance; EDSS: Epworth Daytime Sleepiness Scale; PSQI: Pittsburgh Sleep Quality Index. Data are presented as mean ± standard deviation, along with the mean difference and 95% confidence interval. Intergroup comparisons (between groups) were performed using the independent t-test. The significance level adopted was p < 0.05. Statistically significant differences (p < 0.05) between-group analyses are marked with asterisks (*).
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MDPI and ACS Style

Nóbrega Júnior, J.C.; Brandão, D.; Xavier, D.; Torres, R.; Soares Brandão, S.; Formiga, M.; Fink, J.B.; Ari, A.; Campos, S.; Dornelas de Andrade, A. Respiratory Rehabilitation After COVID-19: Efficacy of Inspiratory Muscle Training on Lung Function, Quality of Life and Sleep Quality: A Randomized Clinical Trial. COVID 2026, 6, 22. https://doi.org/10.3390/covid6010022

AMA Style

Nóbrega Júnior JC, Brandão D, Xavier D, Torres R, Soares Brandão S, Formiga M, Fink JB, Ari A, Campos S, Dornelas de Andrade A. Respiratory Rehabilitation After COVID-19: Efficacy of Inspiratory Muscle Training on Lung Function, Quality of Life and Sleep Quality: A Randomized Clinical Trial. COVID. 2026; 6(1):22. https://doi.org/10.3390/covid6010022

Chicago/Turabian Style

Nóbrega Júnior, Jose Carlos, Daniella Brandão, Daiara Xavier, Roberta Torres, Simone Soares Brandão, Magno Formiga, James B. Fink, Arzu Ari, Shirley Campos, and Armèle Dornelas de Andrade. 2026. "Respiratory Rehabilitation After COVID-19: Efficacy of Inspiratory Muscle Training on Lung Function, Quality of Life and Sleep Quality: A Randomized Clinical Trial" COVID 6, no. 1: 22. https://doi.org/10.3390/covid6010022

APA Style

Nóbrega Júnior, J. C., Brandão, D., Xavier, D., Torres, R., Soares Brandão, S., Formiga, M., Fink, J. B., Ari, A., Campos, S., & Dornelas de Andrade, A. (2026). Respiratory Rehabilitation After COVID-19: Efficacy of Inspiratory Muscle Training on Lung Function, Quality of Life and Sleep Quality: A Randomized Clinical Trial. COVID, 6(1), 22. https://doi.org/10.3390/covid6010022

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