In ultra-endurance sports, simply consuming large quantities of carbohydrates isn't enough to maximize performance; athletes must also be able to assimilate them efficiently. Carbohydrate assimilation capacity refers to how easily these sugars are hydrolyzed to cross the intestinal barrier, where they can be metabolized by the liver and/or stored as glycogen in the muscles. This assimilation capacity is crucial for avoiding gastrointestinal discomfort and ensuring a stable energy supply throughout the duration of the effort.
This article explores the importance of carbohydrates for performance, as well as nutritional strategies to optimize the assimilation of these macronutrients.
Carbohydrates: essential fuel for performance and recovery
For ultra-endurance athletes, carbohydrates are the number one source of energy. Stored as glycogen in the muscles and liver, these reserves are limited and are quickly depleted during exertion.
They will be just as essential and crucial for performance during exertion as they are around exertion:
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Initial carbohydrate availability : To start the effort with the greatest possible energy reserves, it is essential to optimize glycogen stores before exercise. This requires a gradual and appropriate increase in carbohydrate intake over the days leading up to the race. Without this adaptation, the athlete risks experiencing significant fatigue from the very beginning of the event.
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Carbohydrate intake during exercise : Sufficient and regular carbohydrate consumption throughout the exercise allows the athlete to provide the body with the preferred energy substrate in order to maintain a good level of intensity, limit the use of glycogen reserves and thus delay the fatigue felt.
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Post-exercise glycogen resynthesis : Optimal recovery depends on the speed of energy reserve resynthesis. To restore glycogen stores, it is necessary to consume carbohydrates post-exercise. The closer carbohydrate intake is to the end of exercise, the more important it is to choose carbohydrates with a high glycemic index that are rapidly absorbed (such as a recovery drink).
Assimilation capacity: a physiological constraint in ultra-endurance
The ability to assimilate carbohydrates varies from one athlete to another and depends on several factors:
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Gut training : Athletes can train their digestive system to tolerate large amounts of carbohydrates during exercise. This gut training helps reduce the risk of gastrointestinal problems and also allows them to assimilate increasingly higher carbohydrate intakes.
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The type of carbohydrates consumed : Glucose and fructose use different intestinal transporters. This difference allows, by combining these two types of carbohydrates, for increased fuel consumption during exercise. Maltodextrins, on the other hand, are rapidly absorbed, making them ideal for prolonged exertion.
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The duration and intensity of the effort : The intestine's capacity to absorb carbohydrates can be severely tested during intense exercise, due to the redistribution of blood flow to the muscles at the expense of the digestive system. In ultra-endurance sports, it is therefore essential to adjust carbohydrate intake and distribute it evenly to avoid overloading the digestive system and to maximize assimilation capacity.
Adjust intake according to the intensity and duration of the effort.
Depending on the duration and intensity of the effort, the quantity and type of carbohydrates consumed should be adjusted to optimize assimilation and performance:
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Short, high-intensity efforts (< 1 hour) : For this type of effort, carbohydrate intake is not necessary during exercise. However, muscle glycogen stores will be crucial, so it will be necessary to optimize energy reserves beforehand.
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Prolonged low- to moderate-intensity efforts (> 1.5 hours) : Since glycogen reserves are limited, carbohydrates must be supplied from the start and throughout the effort to minimize the use of these reserves and prevent fatigue. Carbohydrate intake per hour of exercise will vary from 30 to 90g depending on the factors discussed previously.
Optimize absorption to prevent digestive problems
Ultra-endurance athletes often experience digestive issues during exercise. To avoid these problems and improve nutrient absorption, several strategies can be implemented:
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Spreading carbohydrate intake : To minimize the risk of digestive problems during exercise, it is essential to distribute carbohydrate consumption throughout the event to maintain a good energy level without being limited by assimilation capacity.
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Choose easily digestible energy sources (and test them beforehand) : Isotonic drinks, fruit compotes, gels, and energy bars, properly dosed and adapted to the effort, are designed to facilitate assimilation. Drinks containing maltodextrin and fructose are particularly beneficial because they allow for faster absorption without overloading any intestinal transporters.
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Adjust the concentration of drinks according to climatic conditions : During periods of intense heat, it may be advisable to reduce the carbohydrate concentration of drinks to avoid dehydration due to excessively high osmolarity. Under normal conditions, a concentration of approximately 30 to 60 g of carbohydrates per liter is optimal.
The importance of the recovery phase for future assimilation capacity
Post-exercise recovery is fundamental to replenish glycogen stores, but also plays a role in adapting assimilation capacity for future efforts.
An intake of 1 g of carbohydrates per kg of body weight within 30 minutes post-exercise, then every two hours, optimizes the resynthesis of energy stores and will train the body to assimilate larger quantities of carbohydrates.
Conclusion
To perform well in ultra-endurance sports, it's not enough to simply consume large quantities of carbohydrates; the body must also be able to assimilate and utilize them efficiently. By adjusting intake according to the intensity of the effort and by improving assimilation capacity through intestinal training, athletes can maximize their performance, delay fatigue, and prevent digestive problems.
The capacity for assimilation thus becomes a pillar of the nutritional strategy in ultra-endurance, allowing athletes to make the most of every gram of carbohydrates consumed.
