Specific contribution of quadriceps muscle strength, endurance, and power to functional exercise capacity in people with chronic obstructive pulmonary disease: a multicenter study.

Abstract

OBJECTIVE\nVarious functional muscle properties affect different aspects of functional exercise capacity in people with COPD. The purpose of this study was to investigate the contribution of quadriceps muscle strength, endurance, and power to the 6-minute walking distance (6MWD) and the 1-minute sit-to-stand test (1STS) performance in people with COPD.\n\n\nMETHODS\nThe study was a prospective, multicenter cross-sectional study. Anthropometrics, Medical Research Council (MRC) dyspnea scale, lung function, 6MWD and the 1STS number of repetitions were assessed. Isometric quadriceps strength (Strength-ISOM) and endurance (Endurance-ISOM), isotonic quadriceps endurance (Endurance-ISOT), isokinetic quadriceps strength (Strength-ISOKIN), and power (Power-ISOKIN) were assessed on a computerized dynamometer while functional quadriceps power was determined during 5 sit-to-stand repetitions (Power-5STS). Univariate and multivariate analyses were performed to determine the contribution of functional muscle properties on the 6MWD and the 1STS number of repetitions.\n\n\nRESULTS\nThe study included 70 people with COPD (mean % predicted FEV1\xa0=\xa058.9 [SD\xa0=\xa018.2]). The 6MWD correlated with each functional muscle property, except the Endurance-ISOM. The number of repetitions during the 1STS correlated with each functional muscle property except isometric measurements. Multivariate models explained respectively 60% and 39% of the variance in the 6MWD and 1STS number of repetitions, with Power-5STS being the muscle functional property with the strongest contribution to the models.\n\n\nCONCLUSION\nExcept for isometric endurance, quadriceps strength, endurance, and power were associated with functional exercise capacity in people with moderate COPD. Among these functional muscle properties, muscle power contributed the most to the 6MWD and 1STS number of repetitions, suggesting that muscle power is more relevant to functional exercise capacity than muscle strength or endurance in people with COPD.\n\n\nIMPACT\nUnderstanding the individual contribution of muscle properties to functional status is important to designing interventions. This study provides the guidance that muscle power may be more important to functional exercise capacity than muscle strength or endurance in people with COPD.