Abstract

Lactate has long been thought to be a waste product of anaerobic glycolysis that causes muscle fatigue, pain, or damage. Later studies clarified that lactate is not a waste product but a fuel created by skeletal muscles and brain astrocyte cells during moderate to intense physical exercises and is one of the primary fuels of the body and brain for energy production. Overall, it has been shown that lactate is a mysterious chemical that plays a more important role than previously thought.

Although there have been significant advances in our knowledge of the metabolites involved in neuronal energy metabolism during recent years, there are still many unknowns about brain energy metabolism due to its complexity.

This study evaluates the effect of exercise on brain and body energy metabolism, especially the fate of lactate and glucose in two regions of the brain (including the posterior cingulate cortex and the supplementary motor area) and plasmatic level.

Previous studies are limited to animal experiments or a result of measuring the difference in arterial lactate concentration in humans, which do not give us a clear understanding of the fate of brain lactate and glucose. In this study, non-invasive imaging techniques, including Magnetic Resonance Spectroscopy and Positron Emission Tomography, were used to understand the concentration of lactate and the rate of cerebral glucose absorption after exercise.

The analyses performed on 29 healthy subjects (between 25 and 45 years of age) indicate an increase in brain lactate concentration and a decrease in brain glucose absorption due to exercise, which once again confirms the claim of replacing lactate instead of glucose as fuel for neurons. In addition, our analysis shows a direct correlation between plasma lactate and brain lactate, from which it can be concluded that plasma lactate is the primary source of brain lactate.

Most importantly, based on the original findings, the increase in lactate and decrease in glucose observed in the brain are considered two independent phenomena occurring in parallel following intense exercise. Although it should be noted that there is a strong relationship between the changes of measured quantitative metabolites and the states of rest or exercise, so with the changes in the concentration of metabolites, we can significantly predict the presence in the state of exercise or rest.