Correlation between quadriceps strength and five exercise tests in subjects with chronic obstructive pulmonary disease (COPD)

Introduction There is interest to understand the correlation between quadriceps strength and exercise performance in subjects with COPD when considering the contribution of peripheral muscle weakness to exercise limitation. Aims and Objectives We wished to compare the relationship between quadriceps strength and different exercise test protocols. Methods Subjects with symptomatic COPD (MRC>3, GOLD Stage >2) were recruited ([ISRCTN 64759523][1]). Subjects performed two symptom-limited tests for the Incremental Shuttle Walk Test (ISWT), Endurance Shuttle Walk Test (ESWT), incremental and constant work ratecardiopulmonary cycle tests (ICE & CWR), Six-Minute Walk Test (6MWT) and Quadriceps Maximal Voluntary Contraction (QMVC). Baseline data were analysed using bivariate correlation. Results 20 subjects (85% male, mean[SD] age 64[6.7]years, FEV1 %predicted 48[16], FEV1/FVC 44[12.2], Body Mass Index 29.3[7.1], median MRC of 3, were studied. There was a significant correlation to QMVC with both the ESWT ( p =0.004, r =0.65; Figure1) ![Figure][2] and CWR loaded duration ( p =0.03, r =0.51). There were no significant correlations between ICE loaded duration or peak oxygen uptake ( p =0.88 and p =0.05 respectively), 6MWT ( p =0.053) or ISWT ( p =0.228). Conclusions There is a significant positive correlation in quadriceps strength to the endurance tests that is not observed in the incremental or 6MWT protocols. [1]: /external-ref?link_type=ISRCTN&access_num=ISRCTN64759523 [2]: pending:yes