title: Greater glucose uptake heterogeneity in knee muscles of old compared to young men during isometric contractions detected by [(18)F]-FDG PET/CT.
abstract: We used positron emission tomography/computed tomography (PET/CT) and [(18)F]-FDG to test the hypothesis that glucose uptake (GU) heterogeneity in skeletal muscles as a measure of heterogeneity in muscle activity is greater in old than young men when they perform isometric contractions. Six young (26 ± 6 years) and six old (77 ± 6 years) men performed two types of submaximal isometric contractions that required either force or position control. [(18)F]-FDG was injected during the task and PET/CT scans were performed immediately after the task. Within-muscle heterogeneity of knee muscles was determined by calculating the coefficient of variation (CV) of GU in PET image voxels within the muscles of interest. The average GU heterogeneity (mean ± SD) for knee extensors and flexors was greater for the old (35.3 ± 3.3%) than the young (28.6 ± 2.4%) (P = 0.006). Muscle volume of the knee extensors were greater for the young compared to the old men (1016 ± 163 vs. 598 ± 70 cm(3), P = 0.004). In a multiple regression model, knee extensor muscle volume was a predictor (partial r = -0.87; P = 0.001) of GU heterogeneity for old men (R (2) = 0.78; P < 0.001), and MVC force predicted GU heterogeneity for young men (partial r = -0.95, P < 0.001). The findings demonstrate that GU is more spatially variable for old than young men and especially so for old men who exhibit greater muscle atrophy.
authors.affiliation: Integrative Neurophysiology Laboratory, Department of Health and Exercise Science, Colorado State University Fort Collins, CO, USA.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Rudroff
authors.affiliation: Integrative Neurophysiology Laboratory, Department of Health and Exercise Science, Colorado State University Fort Collins, CO, USA.
authors.forename: John H
authors.initials: JH
authors.lastname: Kindred
authors.affiliation: Integrative Neurophysiology Laboratory, Department of Health and Exercise Science, Colorado State University Fort Collins, CO, USA.
authors.forename: John-Michael
authors.initials: JM
authors.lastname: Benson
authors.affiliation: Integrative Neurophysiology Laboratory, Department of Health and Exercise Science, Colorado State University Fort Collins, CO, USA.
authors.forename: Brian L
authors.initials: BL
authors.lastname: Tracy
authors.affiliation: Turku PET Centre, University of Turku and Turku University Hospital Turku, Finland.
authors.forename: Kari K
authors.initials: KK
authors.lastname: Kalliokoski
keywords: aging; computed tomography; glucose; muscle volume; positron emission tomography