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 (V(O2)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 V(O2)max (893 +/- 314 mL, 46.0% predicted) and reduced quadriceps force (QF) [65% predicted]. Significant correlates of V(O2)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 Pa(O2) at rest (r = 0.33). In stepwise multiple regression analysis, VC and QF were independent predictors of V(O2)max. Furthermore, in subgroup analysis, QF was a significant contributing factor for V(O2)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.