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Fuelling Endurance Performance

Fuelling long distance races, ultra’s and training runs over 4hrs is crucial for performance and can make the difference between finishing a race strongly and a DNF. When you have invested so much time in training the last problem you want in your race or challenge is poor attention to your nutrition strategies that could lead to a lot of problems ranging from stomach issues to complete energy depletion.

As an endurance athlete you have a store of glycogen going into a race if you have tapered and eaten the day and morning before an event. So how long does this store last? When do I need to start eating in a race? What foods can my body tolerate? These are some of the questions that have been running through my head when I try to put together a nutrition strategy for a long race.


Glycogen stores range between 500-800g in the muscles and 80g in the liver (1). This can be rapidly depleted in 2-3hrs of intense racing and the higher the intensity the greater the demand on Glycogen for energy. Starting early and fuelling at regular intervals will keep up with the demands of energy to ensure performance levels do not diminish.


Carbohydrate (CHO) intake should be the primary focus, through fats and protein are important, more on those later. CHO is used by the body as glucose to produce ATP the energy molecule that is crucial in all aspects of biological work, most importantly during an endurance training session or race for muscle contraction. CHO can be absorbed up to as much as 90g/h (with new recent studies and examples of 120g/h (2))  in two forms 60g from glucose and 30g from fructose to allow for gastric emptying and absorption of nutrients (2). Intake level over this number is likely to cause GI distress and stomach issues. Another very important note is that this level of CHO intake may be far to high for individuals for a number of reasons including fitness levels, temperature, palate fatigue, gastric emptying, external stress and oxidative capacity (3). The good news is that you can train your body to tolerate high levels of CHO intake during endurance events. This means training taking on nutrition whilst running and fine tuning this strategy for your race. All nutrition products (bars, chews, gels) with the correct glucose to fructose ratio will absorb into the body to be used for energy and using a mixture of fuel sources is advised to prevent palate fatigue. Another important note is drink fuel mixtures, a concentration of 6-8% is advisable as solutions over 10% can slow gastric emptying and cause GI distress. A good starting point is 40-50g/hr building up to the maximum you can tolerate, you can also make calculations based on body weight 1-1.2g per kg per hour.


Protein taken alongside carbohydrate during exhaustive or muscle damaging exercise can minimise muscle damage and preserve net protein balance. This is important in mountain or trail ultras due to the muscle damage elicited by eccentric muscle contractions due to the extreme vertical challenges the athlete faces. Protein should be taken in small quantities 0.25g/kg/hr along side CHO 1-1.2 g/kg/hr. Fuel forms can be specific sports products or from real food such as a peanut butter and jam sandwich or bagel with Philadelphia and jam.

Fat is used as a fuel source for intensities below 70% VO2 max an intensity that most athletes would complete an ultra-marathon at. Fat is converted to energy using a process called beta oxidation which yields a high net produce of ATP, the molecule used for muscle contraction. Individuals have a highly abundant storage of fatty acids in the body that can be used for fuelling exercise, even the leanest of athletes. Fat intake during exercise must be practiced and may not be tolerable for many, however if you can train your body to take in a small amount of fat during endurance training and use this in races you can open up a nutritionally dense energy source that will fuel low intensity exercise and also keep you feeling satiated. Another important note is per gram fat will give you the most energy, so if you must carry all your nutrition/food including fat sources will help to keep the weight down.

In a practical sense what do macronutrients look like in terms of nutrition product and real food:

Table 1. (5)


Nutrition during training and competitions can seem like a complicated and daunting task to master but is crucial for performance in long distance ultra’s over 4hrs. Start simple and train your body to take in nutrition on the move, this means practicing and developing your fuelling strategy on a weekly basis. Most gels or chews have around 30g of Carbohydrate from a mix of sources so this can be a good way to measure out quantities initially, though you will want to have a good variety of fuelling options especially in long races. Another very important aspect to consider especially in training is under fuelling will likely compromise recovery leading to reduced quality/consistency in your training, illness or injury.  Ultimately if you can build up to 1-1.2g/kg/hr CHO, 0.25g/kg/hr protein and a small amount of fat you will optimise your performance. Remember to mix your CHO fuel sources and use different forms be it bars, gels, chews, drink mix or real food. Do your research, even if this means just looking at the nutritional information on the back of your gels and bars. Train and practise with your nutrition and the quantities you will aim to take on race day, trying new products or quantities will most likely result in poor performance. Take your fuelling as seriously as training and equipment choices and your body will take you a long way.




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