Exercise intolerance is one of the most devastating consequences of COPD. This has been traditionally attributed to dyspnea and to limitation in ventilation and in gas exchange. Recently, Jones and Killian have shown that for a given level of airflow obstruction, exercise tolerance varies markedly among individuals . Although we found a significant decline in mean value of FEV1 from functional class B to D, we also observed a large overlap of indexes of airflow obstruction between the different functional classes. These observations strongly suggest that other factors are also involved in exercise limitation in COPD. Recent studies have clearly shown that peripheral skeletal muscles are compromised in COPD . Decrease in skeletal muscle mass, strength and mitochondrial enzyme activities have been described, and may play an important role in exercise limitation in COPD . Although the mechanisms underlying this peripheral muscle dysfunction have not been well studied, chronic inactivity is probably one of the most important because similar structural and biochemical changes in peripheral muscles have been described in this condition .