Published randomised controlled trials (RCTs) that compared a specified/quantified intensity of inspiratory muscle training as the only intervention to a sham intervention or no intervention control in adult chronic obstructive pulmonary disease (COPD) patients were eligible for this review. Only those that achieved level of evidence 1b and 2b on Sackett criteria were included.
Training protocols varied greatly between studies, Some studies applied a fixed training intensity (range: 30% to 60% PImax). Other studies used a progressive approach that started at lower intensity (ranging from 15% to 40% PImax) and increased up to 45%, 60% or 100% PImax. Measures included PImax, RV (maximal inspiratory pressure measured at residual volume) and PImax, FRC (maximal inspiratory pressure measured at functional residual capacity). Session duration ranged from 14 to 60 minutes. Study duration ranged from five to 52 weeks.
The percentage of male participants was greater than females. Mean age for treatment and control groups ranged from 41 to 70 years. Outcomes included inspiratory muscle strength measured by PImax, inspiratory muscle endurance measured by incremental threshold loading pressure, inspiratory muscle endurance time at a specified percentage of PImax, maximum sustained inspiratory pressure, health-related quality of life, dyspnoea and exercise tolerance outcomes.
The authors did not state how many reviewers performed study selection.