Fifteen RCTs (n=504) were included in the review.
One trial was not quality assessed as it was only available as an abstract and provided little detail on internal validity. Agreement between reviewers for the quality assessment exercise was 90.7% (kappa statistic 0.72) for all items. The quality of the 14 trials that were assessed was generally poor, with only 3 trials properly or partially describing the randomisation procedure, and only 2 studies partially addressing concealment of treatment allocation. Only one study blinded the outcome assessors and only one study partially reported cointerventions. The majority of studies adequately or partially described a prognostically homogeneous study population and adequately reported patients lost to follow-up.
Endurance exercise versus strength exercise (4 RCTs).
Three studies assessed outcomes using the Chronic Respiratory Questionnaire (CRQ) and were pooled. The pooled results showed statistically significantly larger improvements with strength exercise than endurance exercise in terms of emotional function (WMD -0.38, 95% CI: -0.74, -0.01) and the CRQ total score (WMD -0.27, 95% CI: -0.52, -0.02), but not for the domains dyspnoea, fatigue or mastery. There was no evidence of significant statistical heterogeneity. The number of patients not completing the exercise programme was similar in both the endurance exercise and strength exercise groups.
Endurance exercise versus endurance and strength exercise (7 RCTs).
Five trials had similar exercise protocols for both treatment groups. There were no significant differences between groups in terms of health-related quality of life or functional and maximum exercise capacity improvements, despite 3 trials reporting larger improvements in muscle strength in the groups undertaking endurance exercise plus strength exercise.
Continuous versus interval exercise (3 RCTs).
There were no statistically significant differences between groups undertaking continuous exercise and groups undertaking interval exercise.
High-versus low-intensity exercise (1 RCT).
A small trial of patients with mild COPD found that high-intensity exercise at 80% of maximum exercise capacity yielded statistically significantly greater physiological response in terms of reductions in exercise-induced lactate acidosis and ventilation, and longer endurance time.