Table 2 Characteristics of the included studies

Abodonya et al., 2021

AR: NR 48.05 (8.85)

33/9

Each session has consisted of 6 inspiratory cycles; each cycle has remained around 5 min of resisted inspiration, followed by 60-second rest time intending to improve inspiratory muscle strength. At the fifth and sixth cycle, each patient was instructed to breath regularly as much as possible in tending to improve inspiratory muscle fitness. The inspiratory threshold was controlled by a device loading valve that provided a threshold load with 50% of the MIP

Incentive spirometer exercise

Respironics, Cedar Grove, NJ

Pulmonary function test; dyspnea severity index (DSI); QOL questionnaire: EuroQuality-5Dimensions-3Levels (EQ-5D-3 L);

Functional performance: six-minute walk test (6-MWT)

Post-intervention: short term

McNarry et al., 2022

AR: NR /

46.6 (12.2)

NR

Three unsupervised IMT sessions per week, on nonconsecutive days, for 8 weeks, as in previous studies. Each session involved up to six blocks of six inspirations, with the rest periods interspersing each inspiration progressively decreasing from 40 to 10 s with each block, producing maximum session durations of 20 min. Participants completed as many inspirations as they could prior to failure, defined as not achieving 80% SMIP on three consecutive breaths

Usual care

PrO₂ (PrO₂Fit Health, Smithfield, RI, USA)

Health-related quality of life: King’s Brief Interstitial Lung Disease (K-BILD)

Perceived breathlessness: Baseline Dyspnea Index (BDI) and Transition Dyspnea Index (TDI)

Inspiratory muscle strength;

Physical fitness Estimated: V′O2max (mL·kg − 1 ·min − 1)

Post-intervention: short term

Palau et al., 2022

AR: NR /

50.4 (12.2)

15/11

Train at home twice daily, for 20 min each session, and for 12 weeks using a threshold inspiratory muscle trainer. After the first visit, the subjects will start home-based inspiratory training at a resistance equal to 25–30% of MIP for 1 week

Usual care

Threshold IMT, Respironics)

Lung function: spirometry;

Physical test: VO_2peak test (mL/kg/min);

Health-related Qo: European Quality of Life 5 Dimensions 3 Level Version (EQ-5D-3 L);

Inspiratory muscle strength

Post intervention: short term

Corral et al., 2022

AR: NR

25/63

The regimen was 40 min/day, divided into two 20-min sessions (morning and afternoon), 6 times a week, for 8 weeks. The training load, regardless of whether participants performed IMT or RMT, was individually adapted and increased according to the same distribution scheme for inspiratory and expiratory muscle training; the IMT Group: only inspiratory muscle training; RMT group: training of inspiratory and expiratory muscles

Received a device without resistance (0 cm H₂O) because it lacked a threshold valve

POWERbreathe KH1© device (POWERbreathe International Ltd., Southam, UK)

Quality of life: EuroQol-5D questionnaire;

Respiratory muscle function: inspiratory/expiratory muscle strength; inspiratory muscle endurance);

Physical function: lower and upper limb strength [1-min Sit-to-Stand and handgrip force];

Lung function (forced spirometry);

psychological status

Post-intervention: short term

Costa, 2022

AR: NR

IG: 50.76 (11.28)

CG: 44 (11.28)

13/20

Lung expansion therapy; muscle training Inspiratory: Threshold IMT with 40% of MIP in the 1st, 2nd and 3rd weeks, 50% of MIP in the 4th, 5th and 6th weeks, Three sets of ten repetitions; MMSS strengthening exercises; treadmill

fortnightly lectures, over the six-week period. These meetings were composed of lectures on education in health on various topics related to COVID-19, chronic diseases, quality of life healthy life and lifestyle

Threshold imt (Philips Respironics, EUA)

Lung Function;

Dyspnea: Modified Medical Research Council Dyspnea Scale (mMRC)

Post-intervention: short term

Jimeno-Almazán et al., 2023

AR: NR / 45.30 (8.0)

50/110

CTRM: three-days-a-week concurrent training routine: two days of resistance training [50% 1RM (one-repetition maximum), 3 sets, 8 repetitions, 4 exercises (squat, bench press, deadlift, and bench pull)] followed by moderate intensity variable training [MIVT: 4–6 × 3–5 min at 70–80% heart rate reserve (HRR)/2–3 min at 55–65% HRR], and one day of a monitored autonomous light intensity continuous training (LICT: 30–60 min, 65–70% HRR);

RM: 1 set of 30 repetitions [62.5 ± 4.6% of the PIM (maximum inspiratory pressure)], preceded by a warm-up set, twice a day, every day of the week

CT: same training as the CTMR group, but without respiratory training;

CG: follow the WHO guidelines: “Support for Rehabilitation: Self-Management after COVID-19-Related Illness”

PowerBreathe Classic Heath Series

Anxiety and depression: General Anxiety Disorder Questionnaire-7 (GAD-7) and (Patient Health Questionnaire-9 (PHQ-9);

Dyspnea: Modified Medical Research Council Dyspnea Scale (mMRC);

Fatigue: Fatigue Severity Scale (FSS) and Chalder Fatigue Scale (CFS);

Functional limitations: Post-COVID-19 Functional Status (PCFS)

Post-intervention: short term

Gracelli, 2023

AR: NR

CG: 51.40 (12.80)

IG: 52.0 (13.40)

20/10

IMT: for 6 weeks performing 2 sets of 30 repetitions daily using the POWERbreathe classic medic^® device POWERbreathe InternationalLtd., Southam, UK). Patients exercised at 40% MIP at first week and 60% MIP in the subsequent 5 weeks; Performed respiratory physiotherapy, consisting of the following muscle-strengthening exercises: sitting down and standing up from a chair, abduction of upper limbs with elastic resistance, abduction of limbs lower limbs with elastic resistance and rowing with elastic resistance, were performed 03 series of 10 repetitions of each exercise

Performed respiratory physiotherapy, consisting of the following muscle-strengthening exercises: sitting down and standing up from a chair, abduction of upper limbs with elastic resistance, abduction of limbs lower limbs with elastic resistance and rowing with elastic resistance, were performed 03 series of 10 repetitions of each exercise

POWERbreatheKH2 (POWERbreathe K series KH2^®, HaB International, Warwickshire, Reino Unido)

Respiratory muscle strength and endurance

Post-intervention: short term