Table 1. Basic characteristics of the researches included.
| Investigator | Study design | Study group | Control group | Group size | Participants |
|---|---|---|---|---|---|
| Daniel, 2020 | Prospective, RCT | NMES + PR (treadmill, stationary bicycle, quadriceps resistance training, and breathing exercises) | PR without any stimulation | NMES + PR (n=19); PR (n=19) | Clinically stable COPD, males, 40–75 years, eligibility to participate in exercise training, no acute exacerbations within 3 months |
| Mekki, 2018 | RCT | NMES + PR (comprised motion, stretching, low-intensity aerobic exercises, ergocycle, and interset break) | PR without NMES | NMES + PR (n=25); Control (n=20) | COPD and post-bronchodilator results on spirometry of forced expiratory volume in 1 s/forced vital capacity < 0.7 |
| Valenza, 2018 | RCT | Standard medical treatment + standard rehabilitation program with superimposed NMES | Standard medical treatment based on long-acting bronchodilators without any physical therapy | NMES group (n=18) Control group (n=18) | Stable severe COPD age ranging from 40 to 80 years |
| Bonnevie, 2018 | Single-blind, multicenter randomized trial | PR+NMES group underwent bilateral NMES of the quadriceps muscle at home | Comprehensive PR program (outpatient or home-based) including respiratory physiotherapy, and strength and endurance training on a cycloergometer | PR+NMES (n=27) PR (n=24) |
Severe COPD with forced expiratory volume in 1 s < 60% predicted with a total lung capacity > 80% predicted; baseline modified Medical Research Council dyspnea scale > 1; aged ≥ 18 years |
| Maddocks, 2016 | Double-blind randomized, randomized trial | NMES group received electrical stimulation of the quadriceps of both lower limbs | Placebo NMES (I: 0–20 mA), insufficient to elicit a tetanic muscular contraction | NMES group (n=25) Control group (n=27) |
18 years or older, with a spirometrically defined diagnosis of COPD consistent with GOLD criteria (forced expiratory volume in 1 s:forced vital capacity [FEV1:FVC] < 70%), severe respiratory impairment (FEV1% predicted ≤ 50), and incapacitating breathlessness |
| Kucio, 2016 | RCT | NMES + PR (comprised breathing exercises, treadmill walking and resistance exercise) | PR for 3 weeks without stimulation | NMES + PR (n=15); PR (n=15) |
Hospitalized participants: 11 men, mean FEV1 = 1.66 (SD: 0.69) L, mean age = 68 (SD: 6) yr |
| Tasdemir, 2015 | Double-blind randomized, randomized trial | NMES + cPR (program for 2 days per week over 10 weeks) | cPR: mainly exercise training. Sham NMES using a similar protocol, and the intensity was sufficient to cause a visible twitch muscular contraction | NMES + cPR (n=13); cPR (n=14) |
Medically stable COPD (median FEV1% predicted = 29 (range: 16–71) %, mean age = 62 (SD: 8) yr) |
| Vieira, 2014 | Double-blind randomized, randomized trial | NMES + respiratory physical therapy (i.e., airway clearance) | Respiratory physical therapy + sham NMES (same instruction and electrode position, but no stimulation) | NMES (n=11); control (n=9) | Medically stable COPD (mean FEV1% predicted = 36 (SD: 10) %, mean age = 56 (SD: 11) yr) |
| Sille, 2014 | Prospective, single-blind, RCT | HF-NMES | Strength training (bilateral leg extension and bilateral leg press exercises) | HF-NMES (n=41); control (n=40) |
Not provided |
| Vivodtzev, 2012 | Double-blind RCT | NMES group (bilateral electrical stimulation of the quadriceps (35 min) followed by bilateral stimulation of the calf muscles) | Sham training: the same fashion (5 Hz of frequency in the continuous mode with a 100-μs pulse duration) | NMES (n=12); Control (n=8) |
Medically stable COPD (mean FEV1% predicted = 34 (SEM: 3) %, mean age = 70 (SEM: 1) yr) |
| Vivodtzev, 2006 | Single-blind RCT | NMES (bilateral electrical stimulation of both quadriceps) + rehabilitation 4 days per week for 4 weeks, which comprised active limb exercises | Rehabilitation without any stimulation | NMES + UR (n=9); UR (n=8) |
Medically stable COPD (mean FEV1 = 27 (SD: 3) % predicted, mean age = 59 (SD: 15) yr) |
| Neder, 2002 | Double-blind RCT | NMES (electrical stimulation of both quadriceps) | Usual care, NMES after a control period of 6 week | NMES (n=9); Control (n=6) | Medically stable COPD (mean FEV1% predicted = 38 (SD: 10) %, mean age = 67 (SD: 8) yr) |
| Bourjeily-Habr, 2002 | Double-blind double-blind controlled trial | NMES (electrical stimulation of the hamstrings, quadriceps and calf muscles of both lower limbs) | Sham stimulation same electrode, without any active electrical stimulation | NMES (n=9); Control (n=9) |
Medically stable COPD (mean FEV1% predicted = 36 (SEM: 4) %, mean age = 58 (SEM: 2) yr) |