Randomised controlled trials (RCTs) that compared interval exercise training with continuous exercise training (using standardised protocols) in patients diagnosed with chronic obstructive pulmonary disease (COPD) were eligible for inclusion. More than 90% of trial participants had to be diagnosed with COPD. Criteria for the definition of COPD used in the review was a clinical diagnosis of COPD with: a best recorded forced expiratory volume in one second (FEV1)/forced vital capacity ratio less than 0.70; or a best recorded FEV1 of less than 80% predicted. Trials published in abstract form only, with no other data available, were excluded.
The primary outcome measures evaluated included: peak power, peak oxygen uptake (VO2peak) measured during incremental tests on either a cycle ergometer or a treadmill; functional exercise capacity measured by a six-minute walk test or a 12-minute walk test; health related quality of life as measured by the Chronic Respiratory Questionnaire; and anxiety and depression measured by the Hospital Anxiety and Depression scale. In addition, physiological training effects, skeletal muscle adaptations, and tolerance (compliance, adverse events) were also assessed.
In included trials, the continuous training protocols consisted of moderate to high intensity (50 to 80% of baseline peak power) of durations ranging from 20 to 45 minutes. Interval training protocols typically used high intensity exercise (≥80% of peak power for durations of 20 seconds to three minutes) followed by recovery periods of low to moderate intensity exercise of (30 to 75% peak power) for 30 seconds to three minutes. All but one of the trials used cycle ergometers; the other trial included use of treadmills and cycle ergometers.
Two reviewers performed the study selection.