Submitted on November 27, 2008
Revised on June 11, 2009
Accepted on June 29, 2009
Impact of pre-induced quadriceps fatigue on exercise response in chronic obstructive pulmonary disease and healthy subjects
Philippe Gagnon1, Didier Saey2, Isabelle Vivodtzev1, Louis Laviolette1, Vincent Mainguy1, Julie Milot1, Steeve Provencher1, and Francois Maltais3*
1 Institut Universitaire de Cardiologie et de Pneumologie de Québec
2 Université Laval
3 Institut Universitaire de Cardiologie et de Pneumologie de Québec, Universite Laval
* To whom correspondence should be addressed. E-mail: francois.maltais{at}med.ulaval.ca.
Exercise intolerance in chronic obstructive pulmonary disease (COPD) results from a complex interaction between central (ventilatory) and peripheral (limb muscles) components of exercise limitation. The purpose of this study was to evaluate the influence of quadriceps muscle fatigue on exercise tolerance and ventilatory response during constant workrate cycling exercise testing (CWT) in patients with COPD and healthy subjects. Fifteen patients with COPD and nine age-matched healthy subjects performed, seven days apart, two CWT up to exhaustion at 80% of their predetermined maximal work capacity. In a randomized order, one test was performed with pre-induced quadriceps fatigue and the other in a fresh state. Quadriceps fatigue was produced by electrostimulation-induced contractions and quantified by maximal voluntary contraction (MVC) and potentiated twitch force (TwQpot). Endurance time and ventilatory response during CWT were compared between fatigued and fresh state. Endurance time significantly decreased in the fatigued state compared to the fresh condition in COPD (356 ± 69 sec vs. 294 ± 45 sec, p < 0.05) and controls (450 ± 74 sec vs. 340 ± 45 sec, p < 0.05). Controls showed significantly higher ventilation and end-exercise dyspnea scores in the fatigued condition whereas in COPD, fatigue did not influence ventilation nor dyspnea during exercise. The degree of ventilatory limitation, as expressed by the VE/MVV ratio, was similar in both conditions in patients with COPD. We conclude that it is possible to induce quadriceps fatigue by local electrostimulation-induced contractions. Our findings demonstrate that peripheral muscle fatigue is an additional important factor, besides intense dyspnea, that limits exercise tolerance in COPD.
