Our objective is to investigate the impact of an acute bout of resistance training on key signaling pathways involved in the regulation of muscle mass in moderate to severe COPD (FEV1 under 60% of predicted). Key proteins of signaling intramuscular pathways involved in protein synthesis and degradation will be measured before after 72 contractions of the quadriceps. The exercise protocol was designed to match the actual exercise prescription model use in the context of pulmonary rehabilitation. A squat, leg press and leg extension will be done at 80% of max with one minute rest between sets. A biopsy of the quadriceps will be done before and after exercise in order to measure phosphorylated kinases, total protein content and mRNA expressions. All our patients will undergo a thorough baseline assessment in pulmonary capacity, muscle force and body composition.