Imaging Assessment of Local Brain Metabolic Response to Changing Load During Exercise in Humans

The purpose of this study was to clarify regional changes in brain metabolism induced by ergometer exercise at different loads. To reduce radiation exposure to subjects, we separated our volunteers into two groups: a resting control group and a task group. Three levels of exercise load were designed at 40% (light), 70% (moderate) and 80% (heavy) VO2max, corresponding to aerobic, intermediate and anaerobic metabolic conditions, respectively. The cerebral metabolic rate for glucose was calculated using [18F]fluorodeoxyglucose (FDG) and PET. Regional changes in glucose metabolism were evaluated using statistical parametric mapping (SPM2) with correction for global values. Covariate analysis between FDG uptake and task load identified a strong correlation in the primary motor cortex (precental gyrus) and cingulate cortex. Irrespective of the linearly increased region, strong activations in the motor leg areas were revealed by subtraction analyses during moderate and heavy exercise. Ergometer cycling activated areas in the prefrontal region at light load, and in the premotor, motor and parietal areas at higher loads. These regions are mainly involved in elaboration of movement and are part of the sensory association area for movement. However, activations in the areas responsible for motor control, such as the precentral gyrus were less evident.