Physical exercise is a fantastic way to stimulate our brain function. It has been shown in numerous studies to boost our cognitive skills of memory and learning. Children who exercise are known to perform better academically. Older adults can also boost their memory and thinking skills by undertaking regular exercise of thirty minutes of aerobic activity (enough to get the heart rate up).
Whilst it is known that exercising leads to more oxygen and nutrients getting to the brain, how the brain uses fuel during the actual process of exercise, hasn't been understood until fairly recently.
Our neurons don't store fuel themselves and their primary energy source is glucose. Our brain uses 20% of all the energy we put into our body as fuel, despite only accounting for 2% of our actual body weight. Hence the need to supply our greedy brain with a regular amount of food.
Another discovery a few years back, was that our other brain cells or astrocytes, which act as support agents for our neurons, can store fuel in the form of glycogen. It is this glycogen that is important for the normal function of all of the cells in our brain.
In 2011 scientists from the University of Tsukuba in Japan undertook a study on astrocyte glycogen in rat brains. They suspected that this brain glycogen was used by the neurons as a fuel reserve during times when blood glucose levels were low i.e as in when exercising. In prolonged exercise, our muscular glycogen stores will typically get depleted, so the scientists looked at measuring muscle and brain glycogen in the rats after running them on treadmills at varying intervals of 30, 60 and 120 minutes and comparing levels to a non exercising group.
What they found was that after 30 and 60 minutes of running, the muscle and liver glycogen stores were depleted whilst the rat brain glycogen levels remained the same. But after 120 minutes running, the brain glycogen levels dropped in 5 different areas of brain, consistent with respective blood and brain glucose levels. In other words the glycogen stores from the astrocytes had been broken down and the energy released, and subsequently used by the energy hungry neurons.
In 2012 the same group of scientists did further studies,(again using rats)this time looking at the effect of exhaustive running on brain glycogen levels after a single running session and after 4 weeks of regular moderate intensity running.
After the single session of running on the treadmill, the rats were allowed to rest and feed prior to having their brain glycogen levels measured. What the scientists found was that the rats brains had over compensated with up to 60% more glycogen being stored in the astrocytes. This then dropped back to normal levels within 24 hours. In the second case, after four weeks of exercise training this extra compensation level became the new "normal", especially in those areas of the brain associated with learning and memory. The longer lasting super compensation of the cortex and hippocampus is thought to probably be a training adaptation to meet the increased energy demand of a brain in someone who exercises regularly.
So what does this imply for us as exercising humans?
Having a greater amount of fuel reserve in the astrocytes may explain why our thinking skills improve if we exercise regularly. Our brain then has a better and larger fuel supply to enable us to think and remember better.
So next time you have been for a bit of a burn, don't forget to top up afterwards with a carbohydrate rich snack such as a banana to boost your brain glycogen levels.
Refs: Matsui T, Soya S, Okamoto M, Ichitani Y, Kawanaka K, Soya H. Brain glycogen decreases during prolonged exercise. J Physiol. 2011 Jul 1;589 (Pt 13):3383-93. Epub 2011 Apr 26.
Matsui T, et al. Brain glycogen supercompensation following exhaustive exercise. J Physiol. 2012 Feb 1;590 (Pt 3):607-16. Epub 2011 Nov 7.