Also the similar fatigue resistance in patients with COPD who had stopped smoking and age-, fat-free mass and physical activity-matched healthy controls (Degens et al. 2005) and enhanced maximal oxygen uptake by hyperoxic air if maximal exercise is associated with a reduction of Hb oxygen saturation (Nielsen 2003) are in line with the role of HbCO in muscle fatigue. Here, GSTM1 is linked to chronic obstructive pulmonary disease.