You may have seen images of athletes collapsing because their legs have turned to jelly having to crawl the last part of a race to the finish line. This can be due to glycogen depletion, also known as ‘Hitting the Wall, The Bonk or The Knock’. The reality is far from funny and even the most professional of athletes have at some point in their career, suffered the consequences of glycogen depletion. The cost of glycogen depletion can often be catastrophic to performance. Understanding what it is and what you can do to prevent it, will serve you well, what ever your sporting goals.
Depletion of glycogen stores occurs more often during endurance exercise when the blood glucose levels reach an abnormally low level, this is known as hypoglycaemia. This is due to the body’s glycogen stores (storage form of glucose) being used up in order to fuel the body throughout exercise. These stores can only provide energy for around 90 minutes of endurance exercise before they are exhausted and even less time for intense exercise. Gender, size, age and overall health will also influence the rate at which stores run out.
When glycogen stores become depleted, the body needs to get glucose from other sources. Fat serves as a useful reserve for glucose once glycogen stores are depleted. Fat tissue however is a less efficient energy source as it requires more oxygen to break it down into glucose. Due to this increased oxygen requirement, performance may decline if the athlete is not efficient in burning fat as fuel source or if carbohydrates aren’t consumed to replace lost glycogen stored in the muscles and liver.
Each person will experience hypoglycaemia differently, but there are a number of symptoms typically experienced when blood sugar levels fall low enough to produce adverse affects on the body and prevent it from functioning optimally. The physical symptoms that result include:
Hypoglycemia affects you both physically and mentally because glucose is also the brains preferred energy source, in fact the brain can’t use anything else to fuel it than glucose. However unlike the body, the brain cannot store glycogen either, so it relies on the available glucose in the blood. Therefore when blood glucose levels are low, and the brain doesn’t receive enough glucose, this can result in various psychological symptoms including feeling:
Increasing your carbohydrate intake in the few days leading up to competition will ensure you maximise your glycogen stores. This will delay the point at which glycogen stores become depleted and you hit the wall.
Consuming carbohydrates (sugars) during endurance or intense exercise is essential for maintaining blood glucose levels and topping up glycogen stores, preventing you from hitting the wall. Some of the easiest ways are to consume these carbohydrates in the form of sports drinks and gels as these are easy to take on the move, easy on the stomach and easy to carry with you. 30-60g of high GI carbohydrates should be consumed at regular intervals to prevent the onset of fatigue.
During exercise the body is simultaneously using both glycogen and fat stores for energy. When exercising at a higher intensity carbohydrates (glycogen) usage is increased while fat usage is reduced. Therefore in order to preserve glycogen stores for later on in the race, pace yourself at the start as a lower intensity will increase the use of fat rather than glycogen stores.
In preparation for competition, utilising fat burning sessions during your training can encourage the body to become more efficient in burning fat. A good way to do this is to train in the morning when the body is in a fasted state. This will encourage fat burning due to the lack of glycogen stores. By improving the bodies fat burning ability glycogen stores will be conserved.
It’s important that food or drinks high in sugar are consumed in order to quickly increase blood glucose levels. Sugary foods will rapidly enter the blood stream and symptoms will quickly abate. This should then be followed by snacks or a meal containing carbohydrates, fats and proteins to allow the body to replete your glycogen stores, repair damaged tissues from exercise and help you recover quickly for your next event.
GlycoSource contains both high GI carbohydrates (maltodextrin) and low GI carbohydrates (galactose). When consumed during and after exercise the combination of these two carbohydrates provide a balance of sugars to help maintain blood glucose levels and replenish depleted glycogen stores, helping to prevent hypoglycaemia.
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This article was written by our Nutritionist Bobby Garlington.