Abstract: A total of 13 studies involving 906 participants are included in the review. The trials were different from one another in terms of type of breathing exercise performed, number of participants enrolled, number and duration of sessions completed, outcomes reported and statistical presentation of data. Asthma severity in participants from the included studies ranged from mild to moderate, and the samples consisted solely of outpatients. The following outcomes were measured: quality of life, asthma symptoms, number of acute exacerbations and lung function. Eleven studies compared breathing exercise with inactive control, and two with asthma education control groups. All eight studies that assessed quality of life reported an improvement in this outcome. An improvement in the number of acute exacerbations was observed by the only study that assessed this outcome. Six of seven included studies showed significant differences favouring breathing exercises for asthma symptoms. Effects on lung function were more variable, with no difference reported in five of the eleven studies that assessed this outcome, while the other six showed a significant difference for this outcome, which favoured breathing exercises. As a result of substantial heterogeneity among the studies, meta-analysis was possible only for asthma symptoms and changes in the Asthma Quality of Life Questionnaire (AQLQ). Each meta-analysis included only two studies and showed a significant difference favouring breathing exercises (MD -3.22, 95% CI -6.31 to -0.13 for asthma symptoms; MD 0.79, 95% CI 0.50 to 1.08 for change in AQLQ). Assessment of risk of bias was impaired by incomplete reporting of methodological aspects of most of the included trials. Even though individual trials reported positive effects of breathing exercises, no reliable conclusions could be drawn concerning the use of breathing exercises for asthma in clinical practice. This was a result of methodological differences among the included studies and poor reporting of methodological aspects in most of the included studies. However, trends for improvement are encouraging, and further studies including full descriptions of treatment methods and outcome measurements are required.

Plain-language summary: The trials were different in terms of type of breathing exercises performed, number of participants enrolled, number and duration of sessions completed, outcomes reported and statistical presentation of data. As a result, we were not able to compare the results from these trials using a meta-analysis for all outcomes. Meta-analysis was possible for only two outcomes (asthma symptoms and change in Asthma Quality of Life Questionnaire—AQLQ), each of which was reported in only two studies. Both meta-analyses showed a significant difference favouring breathing exercises. The methods used to conduct these studies were not as well reported as we would have liked, and so the quality of the trials was unclear. Overall the quality of the evidence included in the review was very low. Even though individual trials reported positive effects of breathing exercises, no conclusive evidence in this review supports or refutes the efficacy of such intervention in the treatment of adult patients with asthma.