Diaphragmatic dysfunction and alterations of thoracoabdominal motions are common in patients with chronic obstructive pulmonary disease (COPD). Several studies have described an impairment in diaphragmatic mobility of COPD patients compared to age matched control subjects and it has been associated with increase in dyspnea, exercise intolerance and mortality. COPD patients also experiment a higher activity of the accessory breathing muscles, which greatly increases the work of breathing and dyspnea sensation.

Breathing strategies have been considered an important component of pulmonary rehabilitation and refer to a range of techniques, including/which includes the diaphragmatic breathing (DB). The principal aim of DB is to improve the participation of the abdominal motion while reducing the accessory muscles activity. The role of DB as an adjunctive treatment modality in the rehabilitation of COPD patients remains controversial. Despite the conflicting results, improvement of the abdominal motion and a reduction of thoracic excursion, during voluntarily DB, has been described as a common finding of several studies. The investigators hypothesized that a 4-week DBTP could induce higher participation of the diaphragm and this modification would relieve respiratory symptoms and improve exercise tolerance and the HRQoL. Therefore, in this randomized controlled trial the investigators aimed to test the effects of a short-term DBTP on thoracoabdominal motion, pulmonary function, diaphragmatic mobility, dyspnea, HRQoL and exercise tolerance in patients with mild to severe COPD.

Inclusion Criteria: (1) age between 50 and 80 years; (2) a post-bronchodilator forced expiratory volume in one second (FEV1) < 80% of the predicted value and a FEV1/ forced vital capacity (CVF) ratio < 0,7; (3) stable respiratory/clinical condition without changes in medication and symptoms (dyspnea, volume or color of sputum) for at least 4 weeks before admission to the study; and (4) receiving regular treatment with inhaled bronchodilators and steroids.

Exclusion Criteria: (1) presence of other pulmonary, cardiovascular or musculoskeletal diseases; (2) previously participation in any exercise-training program in the last 2 years before participating in this study; and (3) current smokers.