Brain glycogen decreases during prolonged exercise

Non‐technical summary  Energy sources for the brain include not only blood glucose, but also astrocytic glycogen, especially when the blood‐born glucose supply is short (e.g. hypoglycaemia). Although untested, it is hypothesized that during prolonged exercise that induces hypoglycaemia, the resultant hypoglycaemia may cause a decrease in brain glycogen. Here, we tested this hypothesis and provide evidence that brain glycogen decreases during prolonged exercise with hypoglycaemia. Furthermore, in the cortex, we show that the decrease in brain glycogen levels during prolonged exercise is associated with activation of monoamine metabolism, which could be a factor inducing central fatigue. Since the discovery of muscle glycogen depletion as a candidate of peripheral fatigue during prolonged exercise, this is the first study to our knowledge to show that brain glycogen can decrease with prolonged exercise. These findings may provide a clue towards understanding the mechanisms related to central fatigue.