It is common knowledge that glycogen is the muscles form of energy and therefore fuelling up before exercise is of paramount importance in order to achieve a rigorous level of endurance, but what about the brain? If you take a minute to think about the activity in the old grey matter during each movement you make and the implications this has on energy expenditure, then it’s quite apparent that fuel for the brain is equally as important as fuel for the muscles; after all, if your brain isn’t pumped, then your movements won’t be as slick or as reactive.
Most of us know that during exercise, the muscles use up the readily available glucose (the preferred cellular fuel) in the bloodstream first. They then move on to the stored glycogen, which is stored to some extent in the muscle with further storage in the liver. When you run out of these glycogen stores you reach physical exhaustion; this is known as “hitting the wall” (depleted muscle glycogen) and “bonking” (depleted liver glycogen). What some people don’t realise is that when you workout to exhaustion; you also deplete brain glycogen levels. The brain itself will gorge on the glucose in the bloodstream, therefore restricting the amount available for the working muscle, which eventually turns to stored glycogen. Once the brain has taken all the glucose it can, it then also shifts to local stores of glycogen, produced by neuronal support cells known as astrocytes. A study by Matsui et al. "Brain Glycogen Decreases During Prolonged Exercise" Journal of Physiology, 2011, showed that this has to be exhaustive exercise; 30-60 minutes of treadmill running isn't going to do it.
So, what happens to glycogen stores during recovery? Most of us are aware of the importance of replenishing muscle glycogen for effective recovery and growth, but what about the brain? In another study by Matsui et al. "Brain Glycogen Supercompensation Following Exhaustive Exercise" Journal of Physiology, 2012, the researchers found that the brain is a particularly greedy organ; recovering glycogen stores more speedily than the muscle or liver. The brain fully replenished glycogen stores, even overcompensating a little, in 6 hours, whilst muscle lagged behind at 24 hours to peak, and liver coming in last at 48 hours. It should be apparent from this, why recovering with the relevant amounts of carbs is so important for effective growth; there are 3 lots of stores to replenish and the brain is going to act first, taking all it can and therefore limiting the availability of carbs for the muscle and liver.
The study looked further into the implications that intense, long-term exercise increased glycogen stores in both the muscle and the brain. The subjects (rats) lost weight and fat compared to sedentary rats and they gained glycogen stores in the muscle and in the brain. The authors hypothesize that this long-term overcompensation could be the brain and body's response to the increased energy demands associated with a long-term exercise regiment. Further studies are required, but this increase in brain glycogen stores may well lead to the increased cognitive function that has long been associated with regular exercise.
Recovery & Glycogen Resynthesis
There are many schools of thought when it comes to an athlete's recovery strategy from intense exercise; some go with the notion that the recovery window is particularly short and so you must take full advantage immediately after training, or compromise on gains. However, this doesn’t make a lot of sense given that you would need to ingest around 500-600 grams of carbs to restore glycogen stores to pre-exercise levels and thus facilitate a complete recovery. Therefore, we would suggest there is a much bigger window of opportunity for recovery, which is around 24 hours. This is not to say that the initial couple of hours after training aren’t important and you should definitely be ingesting reasonable amounts of carbs in this period, with a view to continuing a “drip feed” of carbs over the next 20 hours or so between training sessions. Studies tell us around 2% of glycogen is resynthesized each hour that follows the initial 2 hour post-workout recovery period. Taking in around 50 grams every 2 hours after, seems the best protocol for resynthesis and ensures the brain is also adequately satisfied, without becoming too “greedy". There is also evidence to suggest smaller loads of 28 grams every 15 minutes may ramp glycogen repletion rates up further. Please remember, these measures are recommended for athletes engaging in intense exercise and not necessarily for the “average” gym goer.
Carbs For The Brain
Foods such as oats provide a great source of fuel for your brain during and after intense exercise. Oats are broken down slowly and therefore provide a “drip feed” of glucose for the brain, over a longer period of time than other carb sources. Try adding blueberries to your oats for an extra brain boost.
Immediately after training, you should be consuming carbs with a higher glycemic load, such as white rice (or baked white potato). Try adding some raisins here too, as this combination will give a nice kick to insulin and shuttle glucose around the body for uptake by the cells. The trick here is not to provide too sharp a spike in insulin, but just enough so that a rise doesn’t blunt the release of growth hormone. The carb sources you choose in the following hours should include foods such as sweet potato, banana, quinoa, brown rice, carrot and oats (in an order similar to this and according to glycemic load - becoming progressively lower as the day goes).
Fuel your brain and prepare to take over the world!!