Background: Chronic obstructive pulmonary disease (COPD) can lead to peripheral muscle atrophy and weakness. Electrical stimulation (ES) is commonly used to improve muscle function and structure. The purpose of this systematic review is to determine the effect of ES on muscle function, muscle size, fibre characteristics and exercise performance in patients with COPD.
Methods: A search was performed in seven electronic databases (Cochrane Controlled Trials Register, Pubmed, CINAHL, Embase, SPORTDiscus, Web of Science, PEDro). Inclusion criteria were: (1) randomized controlled trials (RCTs), (2) on COPD patients, (3) investigating a defined protocol of ES applied to the lower extremities, (4) analysing at least one main outcome, (5) full text available. Two reviewers extracted the data and evaluated the methodological quality of the studies using the PEDro scale.
Results: The initial search yielded 167 abstracts, of which five RCTs met the inclusion criteria. The mean (SD) methodological quality of the studies was 6.2+1.3 out of 10. Meta-analyses of three studies showed significant increases in muscle torque and walk distance in the ES groups compared to values in the control, sham or other treatment groups. Measures of muscle size revealed equivocal evidence. Patients with less severe COPD tended to show less improvement.
Conclusions: The modest effect sizes after ES, small n, and small number of studies provide weak evidence for the effectiveness of ES to improve lower limb muscle function in COPD patients. Further study should elucidate the optimal parameters for ES protocols and selection criteria for responders and non-responders.