Subjects and Methods: We will study 66 patients diagnosed of COPD with a moderate-severe obstruction (FEV1<60%) and clinically symptomatic. The monitoring will be done for 3 moths. Patients will be differentiated between COPD with "predominant chronic bronchitis" and COPD with "predominant emphysema", with regard to clinical, functional and radiological criteria. After stratification of the sample, patients will be prospectively assigned to three groups of 22 patients each: a) Endurance training group, on cycle ergometer at a workload of 70% VO2max. b) Strength training group, with 5 different weightlifting exercises (4 sets of 6-8 repetitions). c) Mixed training group, with half the time dedicated to each type of training. Training will be developed during 12 weeks, three times per week, in 40 minutes sessions. Analysed variables, at the beginning and at the end of program will be: Chest X-ray, basic blood analyses, electrocardiogram, simple spirometry and bronchodilator test, blood gases, static pulmonary volumes, diffusion measurement and respiratory muscle pressure. Muscle strength will be assessed by means of 1RM test and the Myometer® dynamometer. Using the muscle skeletal ultrasound, we will control changes in muscle fibre size. Maximal and submaximal exercise tests on cycle ergometer will be also performed, so as a walking test (shuttle walking test). At last, we will assess treatment effect on dyspnea (Mahler`s test) and quality of life (CRDQ).