Using Carbohydrates to Fuel Endurance Sport

Whether you’re saddling up for a stage of the tour or rolling out with your mates for 100km, fuelling for performance is crucial. Yet despite the many advancements in the area of sports science and nutrition, the two most common questions I get asked are ‘how should I prepare for a big race?’ and ‘what should I eat on the bike?’

Over the next few weeks I will be looking at some of the more popular fuelling regimes and address what the latest research is saying in this area.

Words - Lori Hill     Images - Rosie Price

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The concept of carbohydrate-loading was first seen in the 1960’s when a Swedish exercise physiologist by the name of Gunvar Ahlborg discovered a direct, positive correlation between the amount of glycogen stores in the body and ones endurance capacity.  Interestingly prior to this, while sports scientists and coaches of endurance athletes had been prescribing carbohydrate rich diets to endurance athletes in the days leading up to an event, they were unaware of the mechanisms as to why this aided athletic performance.

Despite Alborg’s findings leading to a more sophisticated carbohydrate loading protocol, sports scientists over the last 5 decades have since made even greater advancements in this area and gone are the days where athletes chow down on a large bowl of pasta and a loaf of white bread in the days before a big race.


In any endurance exercise lasting 30 min or more, the most common contributors to fatigue are dehydration and glycogen depletion, whereas other factors such as gastrointestinal problems, hyperthermia, and hypernatremia (low sodium concentration) can reduce performance and must be considered in any events lasting more than 4 hours.

It is believed that high intra-muscular and liver stores of glycogen are beneficial for endurance activities however; the best way to do this is not via Ahlborg’s traditional super-compensation method, particularly if the event is in excess of 90 minutes. However, the concept of carbohydrate loading, which is centered on maximizing muscle glycogen stores prior to an endurance competition, is one that is very much misunderstood and as a result often misused.

In fact it is not uncommon for athletes to complain about feeling bloated or ‘heavy’ when following a traditional carbohydrate-loading regime, which is primarily due to the water that is stored in the body alongside the glycogen molecules and it is for reason that I do not prescribe this as a solution for my athletes. 

Yet while there has been a shift more recently by some in the industry from carbohydrates to fat oxidation or fat adaption, of which I will address in coming articles, current research continues to demonstrate that an increase of 150-200mmol/kg of glycogen stored in the body, improves optimal performance in endurance events by 2-3 per cent. However, modern day ‘carb-loading’ regimes are more heavily focused on the development of an appropriate taper period coupled with a quality nutrition program that is both high in carbohydrates, protein and fats.


In recent years research in the area of ‘in-race fueling’ has suggested that in prolonged events, lasting 2.5 hours or more, well trained, competitive athletes, should look to increase their intake of carbohydrates to 90g/hr. Additionally research has also shown that a 2:1 glucose/maltodextrin: fructose ratio should also be utilized to promote carbohydrate oxidation.

This new regime not only increases the efficiency of oxidation but also enhances fluid ingestion and has been shown to reduce gastrointestinal (GI) upset, along with improving performance and reducing fatigue. However in events lasting 1-2 hours athletes require substantially less carbohydrates to maximize performance, (30g/hr) yet must continue to utilize to the 2:1 fructose ratio.


The first 1-2 hours post race are critical for an athlete’s recovery for a number of different reasons and with the quantity of carbohydrates needed at this stage varying extensively between individuals, post race glycogen refueling can range anywhere between 5-12g/kg. However, during this time it is important that an athlete consumes some quality HGL (high glycemic load) foods along with some clean protein at a ratio of 4:1.

Following the first 1-2 hours the introduction of more protein and fats is recommended along with antioxidants (sans red wine) to assist in limiting the amount of oxidative stress occurring within the body and to enhance recovery.


Hydration is crucial for keeping levels of electrolytes, sodium, potassium, calcium, magnesium and also carbohydrates topped up. However in addition to this if the body becomes dehydrated the blood becomes viscous, the process of removing of exercise-derived waste products from the body becomes hindered.  Therefore, to prevent dehydration, even during colder months/climates it is critical that you start each race day fully hydrated. The best method is to slowly consume beverages (~5-7ml/kg) around 4 hours prior to start of the race although; it is also important to keep a close eye on your urine colour/smell and if it appears you are still dehydrated consume a further 4ml/kg 2 hours prior to race start.

If you are an athlete who prefers racing on pre-packaged products such as sports drinks and gels, there are several different types of ‘beverages’, which you will need to utilize for different circumstances:

Isotonic: this is what the majority of sports drinks are. They contain the appropriate balance of electrolytes, carbohydrates (fast) and fluids to hydrate the blood (around 5-8%). These drinks quickly restore the lost fluids and minerals along with providing carbohydrates (HGL) for energy production. They are best consumed in the hour post exercise along with during the race, particularly if you are racing in a warm environment.

Isotonic drinks sit in the middle of the absorption spectrum with water being the most readily available and gels being the least absorbable and designed for carbohydrate supply over hydration.

Hypertonic: These are taken during the race as they are primarily intended to supplement the athletes’ diet to provide extra carbohydrates (typically <8% concentration) to top up intra-muscular stores of glycogen.

As these are absorbed more slowly than water they need to be taken with fluids, and while isotonic drinks will enhance this absorption rate, it is important to alternate with water as you can throw out the pressure gradient between the gut and blood which can lead to Gastrointestinal upset.  Gels can also be taken 30-60 minutes prior to racing and in the first hour post race to aid re-fuelling.

Hypotonic: while most sports drinks are isotonic some athletes prefer to utilize hypotonic as they contain much less sugar (around 4%). These drinks provide little carbohydrates but as they are more readily absorbed, when compared to water, they help to rehydrate and quench your thirst. These drinks are more suited to short duration exercise or during the evening to help rehydrate the body (if carb stores are topped up).

Research shows that post race drinks should contain high levels of carbohydrates (HGL) electrolytes and some protein. Consuming beverages that contains a 4 to 1 ratio of carbohydrates to protein is optimal for recovery.