Effect of acute hyperoxia during exercise on quadriceps electrical activity in active COPD patients N. Gosselin, 1 F. Durand, 2,3 , M. Poulain, 1,3,4 , K. Lambert, 3 F. Ceugniet, 4 C. Pre ´ faut 3 and A. Varray 1 1 Laboratoire ‘Sport, Performance, Sante ´’, Montpellier, France 2 Laboratoire ‘Sport, Altitude, Sante ´’, De ´partement STAPS, Font Romeu, France 3 UPRES-EA 701, Laboratoire de ‘Physiologie des Interactions’, Service Central de Physiologie Clinique, Ho ˆpital Arnaud de Villeneuve, Montpellier Cedex, France 4 Clinique du Souffle ‘La Solane’, Osseja, France Received 2 October 2003, accepted 16 March 2004 Correspondence: N. Gosselin, Laboratoire ‘Sport, Performance, Sante ´’, Faculte ´ des Sciences du Sport, 700 avenue du Pic Saint Loup, 34090 Montpellier, France. Abstract Aims: This study investigated whether acute hyperoxia improves electrical muscle activity in active chronic obstructive pulmonary disease (COPD) patients with mild hypoxemia (rest PaO 2 ¼ 9.1  0.4 kPa). Methods: Two identical incremental exercise tests were performed by nine patients while breathing either air or 30% oxygen. Pulmonary gas exchanges, venous concentrations of lactate and pyruvate, and the elec- tromyographic signal of the quadriceps muscle (vastus lateralis and vastus medialis) were sampled each minute. Results: Peak working capacity increased significantly in hyperoxia (94.4  5.2W) compared with normoxia (85.4  5.8W, P < 0.01). During hyperoxic exercise and for a given work load, oxygen uptake was increased (P < 0.001) and ventilation decreased (P < 0.05). Lactate concentration was significantly decreased (P < 0.01) at isowork level and during recovery (respectively – 26% and at least – 15%). In the quadriceps muscle, M-wave amplitude (P < 0.05), root mean square (P < 0.01) and root mean square/ oxygen uptake ratio (P < 0.001) were significantly increased during hyper- oxic exercise compared with room air. Although median frequency values did not differ between conditions, the median frequency was significantly decreased for higher exercise intensity in hyperoxic condition. These mod- ifications reflected better aerobic metabolism, later emergence of muscle fatigue, and greater muscle excitability and activation for the same level of exercise under hyperoxic condition. Conclusion: These data suggest that the acute addition of oxygen in active COPD patients improves their muscle electrical activity during dynamic exercise. Hypoxemia-induced skeletal muscle dysfunction most probably acts through mechanisms based on oxygen availability. Keywords dynamic exercise, EMG, M-wave, respiratory disease, skeletal muscle. Chronic obstructive pulmonary disease (COPD) patients present skeletal muscle abnormalities generally described as reduced oxidative capacity and early activation of the glycolytic pathway (Maltais et al. 1998). Recently, the surface electromyographic (SEMG) technique allowed scientists to identify early abnormalities in quadriceps electrical excitability and activity in sedentary and mildly hypoxemic COPD patients during exercise testing (Gos- selin et al. 2003). The same exercise performed by healthy subjects matched by age and physical activity level did not induce muscle electrical abnormalities. Among the electromyographic difference in explanatory elements Acta Physiol Scand 2004, 181, 333–343 Ó 2004 Scandinavian Physiological Society 333