Chronic Obstructive Pulmonary Disease (COPD) is a major cause of morbidity and mortality worldwide. Moderate to severe COPD patients demonstrate severe impairments in exercise performance in daily activities, significantly affecting their quality of life. There are several causes for this limitation found in literature: air-flow limitation, lung hyperinflation, respiratory and peripheral muscles weakness, among others. In this study we intended to identify the potentially relevant factors that influence exercise performance in a group of moderate to severe COPD patients. We studied 24 male patients, 64,13 + 8,46 years old (46-83 years), FEV1: 46,96 + 12,99% predicted, FRC: 144,71 + 26,86% predicted, DLCO: 69,88 + 16,49 % predicted, PaO2: 78,25 + 7,82 mmHg, PaCO2: 40,78 + 4,28 mmHg. Patients performed an incremental symptom-limited cycle exercise. We correlated rest and exercise lung function parameters with peak oxygen uptake, maximal work rate and time span to exertion. The main contributors to exercise limitation were gas exchange abnormalities, ventilatory limitation and smaller values of body mass index. Rest lung hyperinflation didn't correlate with exercise performance. Dynamic exercise hyperinflation contributed greatly to exercise intolerance, through progressive restriction to tidal volume expansion necessary to deal with increasing exercise metabolic demands. Rest lung function parameters didn't correlate with exercise performance, stressing the importance of cardio-pulmonary exercise testing in the detection of exercise limitation factors in each patient. The identification of exercise limitation factors will certainly contribute to towards defining the best therapeutic approach in COPD patients.