Redistribution of whole-body energy metabolism by exercise: A positron emission tomography study

Objective: Our aim was to evaluate changes in glucose metabolism of skeletal muscles and viscera induced by different workloads using ¹⁸F-2-fluoro-2-deoxyglucose ([¹⁸F]FDG) and three-dimensional positron emission tomography (3-D PET). Methods: Five male volunteers performed ergometer bicycle exercise for 40 min at 40% and 70% of the maximal O₂ consumption ( V̇O_2max). [ ¹⁸F]FDG was injected 10 min later following the exercise task. Wholebody 3-D PET was performed. Five other male volunteers were studied as a control to compare with the exercise group. The PET image data were analyzed using manually defined regions of interest to quantify the regional metabolic rate of glucose (rMRGlc). Group comparisons were made using analysis of variance, and significant differences (P < 0.05) were determined using Scheffe's test (post hoc analysis). Results: Quantitative analysis demonstrated that rMRGlc increased (P < 0.05) in the skeletal muscles of the thigh at mild or moderate workloads when compared with the resting controls. For visceral organs such as the liver and brain, metabolic reduction was significant (P < 0.05) at mild and/or moderate exercise workload. Conclusions: The present study demonstrated linear increases or decreases in glucose uptake by skeletal muscles and viscera with mild and moderate exercise workloads, suggesting the presence of homeostatic energy metabolism. This result supports the finding that [ ¹⁸F]FDG-PET can be used as an index of organ energy metabolism for moderate exercise workloads (70% V̇O_2max). The results of this investigation may contribute to sports medicine and rehabilitation science.