PET/CT imaging of age- and task-associated differences in muscle activity during fatiguing contractions

Abstract

The study compared positron emission tomography/computed tomography (PET/CT) of [(18)F]-2-fluoro-2-deoxy-D-glucose ([(18)F]-FDG) uptake by skeletal muscles and the amount of muscle activity as indicated by surface electromyographic (EMG) recordings when young and old men performed fatiguing isometric contractions that required either force or position control. EMG signals were recorded from thigh muscles of six young men (26 ± 6 yr) and six old men (77 ± 6 yr) during fatiguing contractions with the knee extensors. PET/CT scans were performed immediately after task failure. Glucose uptake in 24 leg muscles, quantified as standardized uptake values, was greater for the old men after the force task and differed across tasks for the young men (force, 0.64 ± 0.3 g/ml; position, 0.73 ± 0.3 g/ml), but not the old men (force, 0.84 ± 0.3 g/ml; position, 0.79 ± 0.26 g/ml) (age × task interaction; P < 0.001). In contrast, the rate of increase in EMG amplitude for the agonist muscles was greater for the young men during the two contractions and there was no difference for either group of subjects in the rate of increase in EMG amplitude across the two tasks. The imaging estimates of glucose uptake indicated age- and task-dependent differences in the spatial distribution of [(18)F]-FDG uptake by skeletal muscles during fatiguing contractions. The findings demonstrate that PET/CT imaging of [(18)F]-FDG uptake, but not surface EMG recordings, detected the modulation of muscle activity across the fatiguing tasks by the young men but not the old men.

Differential contributions of ankle plantarflexors during submaximal isometric muscle action: A PET and EMG study

“…This is consistent with Rudroff et al (2013) who concluded that PET was more sensitive, than SEMG, in revealing modulation of physical activity in thigh muscles during fatiguing contractions of knee extensor muscles at 25 % MVC force. In the current study, PET findings compared to SEMG are evident in figure 5.…”

“…Skeletal muscle glucose uptake is increased during exercise due to a coordinated rise in glucose delivery rate, surface membrane glucose uptake, and intracellular substrate flux through glycolysis (Rose & Richter 2005). Since skeletal muscle glucose uptake rises in parallel with exercise intensity, it reflects muscle's metabolic activity (Kemppainen et al 2002) (Hargreaves 1998, Pappas et al 2000, Fujimoto et al 2000, Kemppainen et al 2002, Hannukainen et al 2005, Kalliokoski et al 2007, Bojsen-Møller et al 2010a, Rudroff et al 2013). …”

Blood flow and muscle oxygenation during low, moderate, and maximal sustained isometric contractions

“…We observed exercise-induced increases in blood flow at the level of the conduit artery, but measurement of gross flow at this site does not indicate how much of the added blood actually perfused the contracting muscle. The concurrent examination of muscle oxygenation allowed us to speculate on perfusion, but the combination of Doppler ultrasound and NIRS does not approach the precision of PET, which can show the distribution of blood in a muscle during a sustained isometric contraction (14,20,21).…”

Glucose uptake heterogeneity of the leg muscles is similar between patients with multiple sclerosis and healthy controls during walking

“…[ 18 F]-FDG uptake reveals the utilization of ordinary glucose, a major energy source for the human body. Therefore, PET with [ 18 F]-FDG can identify inefficient muscle activation strategies which may play an important role in impaired walking performance and greater fatigability in patients with MS [9, 10, 11]. PET/[ 18 F]-FDG can provide insight into muscle fiber (motor unit) activity by examining the spatial distribution of [ 18 F]-FDG within a muscle [12, 13].…”