In vivo imaging of glycogen in human muscle
Chongxue Bie, Yuxuan Ma, Peter C.M. van Zijl, Nirbhay N. Yadav, Xi Xu, Hairong Zheng, Dong Liang, Chao Zou, José L. Areta, Lin Chen, Yang Zhou
Abstract
Probing regional glycogen metabolism in humans non-invasively has been challenging due to a lack of sensitive approaches. Here we studied human muscle glycogen dynamics post-exercise with a spatial resolution of millimeters and temporal resolution of minutes, using relayed nuclear Overhauser effect (glycoNOE) MRI. Data at 5T showed a homogeneous distribution of glycogen in resting muscle, with an average concentration of 99 ± 13 mM. After plantar flexion exercise following fasting with recovery under fasting conditions, the calf muscle showed spatially heterogeneous glycogen depletion and repletion kinetics that correlated with the severity of this depletion. Three types of regional glycogen kinetics were observed: (i) single exponential repletion (type a); (ii) biphasic recovery of rapid repletion followed by additional depletion (type b); (iii) biphasic recovery where continued depletion is followed by an exponential recovery (type c). The study of the complex patterns of glycogen kinetics suggests that glycogen breakdown may be quantitatively important during the initial recovery. The non-invasive spatial measurement of glycogen in humans has been challenging due to a lack of sensitive approaches. Here, the authors characterize regional glycogen dynamics in human muscle under exercise using MRI, providing insights into the complex patterns of muscle energy consumption and recovery.