title: Impact of preinduced quadriceps fatigue on exercise response in chronic obstructive pulmonary disease and healthy subjects.
abstract: 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, 7 days apart, two CWTs up to exhaustion at 80% of their predetermined maximal work capacity. In a randomized order, one test was performed with preinduced quadriceps fatigue and the other in a fresh state. Quadriceps fatigue was produced by electrostimulation-induced contractions and quantified by maximal voluntary contraction and potentiated twitch force (TwQ(pot)). Endurance time and ventilatory response during CWT were compared between fatigued and fresh state. Endurance time significantly decreased in the fatigued state compared with the fresh condition in COPD (356 +/- 69 s vs. 294 +/- 45 s, P < 0.05) and controls (450 +/- 74 s vs. 340 +/- 45 s, 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 or dyspnea during exercise. The degree of ventilatory limitation, as expressed by the Ve/maximum voluntary ventilation 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.
authors: Centre de Recherche, Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, Québec G1V 4G5 Canada.
authors: Philippe
authors: P
authors: Gagnon
authors: Didier
authors: D
authors: Saey
authors: Isabelle
authors: I
authors: Vivodtzev
authors: Louis
authors: L
authors: Laviolette
authors: Vincent
authors: V
authors: Mainguy
authors: Julie
authors: J
authors: Milot
authors: Steeve
authors: S
authors: Provencher
authors: François
authors: F
authors: Maltais
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D001642:Bicycling / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D009043:Motor Activity / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology* / Q000503:physiopathology*; D010807:Physical Endurance / Q000502:physiology; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012129:Respiratory Function Tests; D015656:Respiratory Mechanics / Q000502:physiology