The aim of this study was to explore how respiratory muscle training has been studied in adults with COPD, stage 1-4, regarding methods, outcome measurements, theoretical perspective and methodology. This to get a better understanding of how respiratory muscle training can be used in clinical work, and for future research to conduct studies of good methodological quality, which can provide better probative.Method: This literature review included studies which were published after the literature search of the Cochrane report, "Breathing exercises for chronic obstructive pulmonary disease" was closed (April 2012). Eleven studies were included with the keywords: chronic obstructive pulmonary disease, breathing exercises and respiratory muscle training, from the following databases: PubMed, Cinahl, Pedro, AMED, SweMed+ och PSYCInfo.Result: The studies shows that the respiratory muscle training combined with physical activity has a positive value for people with COPD concerning functional exercise capacity, health-related quality of life, lung function and reduction of the number of exacerbations. Exercise used in the studies are yoga, tai chi/qigong, breathing resistance on inhalation and/or exhalation and deep breathing techniques. All of the included studies had low quality due to the methodology. Several different outcome measures are used for similar outcomes, which complicates the comparison of the different studies.Keywords: chronic obstructive pulmonary disease; breathing exercises; respiratory muscle training.