title: Scaling skeletal muscle function to mass in patients with moderate-to-severe COPD.
abstract: Skeletal muscle performance and muscle mass are commonly reduced in patients with advanced chronic obstructive pulmonary disease (COPD). It is currently unclear, however, whether negative changes in muscle structure and function are proportionately related to each other in these patients. In a cross-sectional study, 39 patients (post-bronchodilator FEV1=49.7+/-15.5% pred) and 17 controls were submitted to knee isokinetic dynamometry [peak torque (PT), isometric strength (IS), and total work (TW)] and dual energy X-ray absorptiometry for the evaluation of leg muscle mass (LMM). Muscle function (F) was normalised for LMM by using ratio standards (F.LMM-1), power function ratios (F.LMM-b, where b is usually not equal 1), and analysis of covariance (ANCOVA). Patients with COPD presented with reduced PT, IS, TW, and LMM as compared to controls: there were significant linear correlations among these variables in both groups (P<0.05). Ratio standards of PT.LMM-1 and TW.LMM-1 were, on average, 14% lower in patients than controls (P<0.01). The coefficients for allometric correction of IS and TW were significantly higher in patients as compared to controls (0.975 vs. 0.603 and 1.471 vs. 0.824, respectively, P<0.05), i.e. more LMM was needed to generate a given functional output in patients than normal subjects. In addition, adjusted means of muscle function variables by ANCOVA were 11-18% lower for patients than controls with LMM as the covariate (P<0.05). We conclude that factors other than simple atrophy (i.e. mass-independent mechanisms) might play a role in explaining the COPD-related skeletal muscle dysfunction.
authors.affiliation: Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Division of Respiratory Diseases, Department of Medicine, Federal University of Sao Paulo (UNIFESP), São Paulo - Paulista School of Medicine, Brazil.
authors.forename: Carla
authors.initials: C
authors.lastname: Malaguti
authors.forename: Luiz E
authors.initials: LE
authors.lastname: Nery
authors.forename: Simone
authors.initials: S
authors.lastname: Dal Corso
authors.forename: Lara
authors.initials: L
authors.lastname: Nápolis
authors.forename: Marcelo Bicalho
authors.initials: MB
authors.lastname: De Fuccio
authors.forename: Marise
authors.initials: M
authors.lastname: Castro
authors.forename: J Alberto
authors.initials: JA
authors.lastname: Neder
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D000886:Anthropometry; D001823:Body Composition / Q000502:physiology; D003430:Cross-Sectional Studies; D003627:Data Interpretation, Statistical; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000503:physiopathology*; D009929:Organ Size / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology; D011653:Pulmonary Diffusing Capacity / Q000502:physiology; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012129:Respiratory Function Tests; D013147:Spirometry