Quadriceps weakness is related to exercise capacity in idiopathic pulmonary fibrosis

Study objective: In COPD, it has been shown that peripheral muscle dysfunction is a factor determining exercise intolerance. We examined the hypothesis that exercise capacity of patients with idiopathic pulmonary fibrosis (IPF) is, at least in part, determined by peripheral muscle dysfunction. Methods: Maximum oxygen uptake (VO(2)max) was evaluated in 41 consecutive patients with IPF, along with potential determinants of exercise capacity, both in the lungs and in the peripheral muscles. Results: Patients had reduced VO(2)max (893 +/- 314 mL, 46.0% predicted) and reduced quadriceps force (QF) [65% predicted]. Significant correlates of VO(2)max reduction were vital capacity (VC) [r = 0.79], total lung capacity (r = 0.64), diffusion capacity (r = 0.64), QF (r = 0.62), maximum expiratory pressure (r = 0.48), and PaO2 at rest (r = 0.33). In stepwise multiple regression analysis, VC and QF were independent predictors of VO(2)max. Furthermore, in subgroup analysis, QF was a significant contributing factor for VO(2)max in patients who discontinued exercise because of dyspnea and/or leg fatigue. Conclusions: We conclude that QF is a predictor of exercise capacity in IPF. Measures that improve muscle function might improve exercise tolerance.