It has been shown that peripheral muscle dysfunction is a critical factor in determining exercise intolerance in patients with several chronic lung diseases, including idiopathic pulmonary fibrosis. We hypothesized that exercise capacity would be, at least in part, determined by peripheral muscle dysfunction in patients with fibrotic nonspecific interstitial pneumonia (f-NSIP), another major subtype of fibrotic interstitial lung disease. The aim of the current study was to elucidate the relevance of peripheral muscle dysfunction and its contribution to exercise intolerance in f-NSIP.

The six-minute walk test was evaluated in 30 consecutive patients with f-NSIP along with potential determinants of exercise capacity, including respiratory muscle force and peripheral muscle force.

Among 30 patients, the median age was 61 years, and 21 were female. Sixteen patients showed significantly decreased quadriceps force (QF), and 17 had significant decreases in maximum expiratory pressure. Exercise capacity and muscle power were clearly related to sex. Adjusted for sex, QF showed a significant relation to exercise capacity measured by six-minute walk distance (6MWD), whereas pulmonary function parameters such as vital capacity showed marginal correlations. In stepwise multiple regression analysis, only QF was an independent predictor of 6MWD.

Quadriceps weakness is often observed in patients with f-NSIP. It seems that QF significantly contributes to exercise capacity in this population.