This blog will hopefully stop you making the big mistake far too many marathon runners make! Race nutrition is an aspect of marathon nutrition many leave until too late. Many only start thinking about it close to the marathon but this is a big no no! This is far too late. You need to start now.
The main cause of fatigue in exercise over 60 min is depleting energy stores. Our body mainly uses carbohydrate and fat for energy. Although we use a mix of both energy sources, carbohydrate is the dominant source as it is more readily converted to energy than fat. We generally have a small amount of glucose circulating in the blood, with most being stored in the muscle and liver as glycogen. However, here lays the problem. We only have enough stored carbohydrate to last about 90 min of exercise compared to fat where energy stores should theoretically power a runner for at least 1300kms! This could lead us to thinking we should rely less on carbs and become more proficient at using fat for energy!
It may seem to make sense but the importance of carbohydrate in exercise performance has been reported as early as 1939 (1), and one should not ignore the endless number of studies since that prove carbohydrate taken during prolonged exercise increases time to exhaustion.
In simple terms, when glycogen stores become depleted, your muscles and brain run out of fuel, making us feel exhausted and drained. In an ideal scenario, if we take carbs when on the move we minimise this depletion by keeping the blood sugar level up, keeping stores a plenty and energy levels flowing.
The longer we can keep our stored carbohydrate, the better we will be fuelling when we race. If we can keep our blood sugar levels topped up, we can keep saving our stored carbohydrate for later in the race. With this in mind, it is important to maintain your energy levels as early as possible in the race. If you are waiting to take your first gel or drink until an hour into your run, your glycogen stores will already be getting low. The key is to start early at about 20 minutes into the race. Although you won’t necessarily be feeling low on energy, topping up the tank from the word go will only benefit you later in the race where fuelling may become harder due to fatigue and potential stomach problems.
The general recommendation to take between 30-60g of carbohydrate per hour during prolonged exercise. These recommendations are based on the fact that the body cannot absorb more than 60g of carbohydrate per hour (1g/min) when taking a single carbohydrate source such as glucose. However, during further prolonged exercise (those of you that run longer than 2.5hrs), if a “multiple” or “dual” carb source is consumed such as maltodextrin:fructose together, we can utilise up to 90g/hr instead of 60g/hr with a single source carb. This is because the two different types of carbs (maltodextrin + fructose) use different intestinal transporters for absorption hence increasing carbohydrate delivery and use. In reality though, this is a large amount of carbohydrate and probably not managed by many, but you can train your gut, so practice in training will see what you can tolerate.
In light of all of this evidence, does it mean that if you can’t manage these amounts all is lost? The answer is no. If you find you really struggle to tolerate anything apart from water at certain points of the race, evidence has suggested that even rinsing the mouth with a carbohydrate drink (without swallowing) could trick you brain into thinking it’s receiving energy and have an improvement on your performance!
Individuality rules! First, experiment and see what works for you. Gels, energy chews, sport drinks, bars, real food…it is personal choice and down to tolerance and taste. Sports products are designed for fast absorption and ease of use but some people dislike them and find real food is the way forward. Sports drinks tick both boxes of fuelling and hydration and are a good base for your fuelling plan. If you are doing a race that provides drinks and food, find out what they are and train with that specific brand. This may mean that you can rely on the pit stops rather than carrying your own. Avoid anything that has high levels of protein or fibre, such as some energy bars, as these will slow down the absorption rate of your needed carbohydrate.
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