The rate of carbohydrate oxidation is one of the main factors that determine performance in endurance sports. During prolonged exercise, the body’s ability to use carbohydrates as an energy source can be the difference between maintaining pace or entering fatigue. But what actually limits this process?
What is carbohydrate oxidation rate
Carbohydrate oxidation rate refers to how quickly the body is able to use ingested or stored carbohydrates to produce energy during exercise.
In endurance activities, especially at moderate to high intensities, carbohydrates are the primary energy source. However, this process is not unlimited and depends on several physiological factors.
Main factors that limit carbohydrate oxidation
Intestinal absorption capacity
One of the main bottlenecks is the intestine. There is a limit to how much carbohydrate can be absorbed per hour.
Transporters such as SGLT1 and GLUT5 are responsible for absorbing glucose and fructose. When only one type of carbohydrate is consumed, absorption tends to reach saturation more quickly.
For this reason, combining different types of carbohydrates can increase absorption rate and, consequently, energy availability.
Gastric emptying
Before being absorbed, carbohydrates need to leave the stomach. This process can be influenced by high carbohydrate concentration, dehydration, and exercise intensity.
When gastric emptying is reduced, energy delivery is also compromised.
Muscle utilization capacity
Even when carbohydrates reach the bloodstream, they still need to be used by the muscles.
Factors such as training status, mitochondrial density, and metabolic adaptations directly influence this capacity.
Trained athletes are able to oxidize more carbohydrates per hour than untrained individuals.
Glycogen availability
Muscle and liver glycogen stores are also key factors.
As exercise duration increases, these stores are depleted, increasing reliance on carbohydrate intake during activity.
When this intake is insufficient, performance decline becomes inevitable.
Inadequate nutritional strategy
Consuming too little carbohydrate or consuming it at the wrong times directly limits carbohydrate oxidation rate.
Additionally, lack of gut training can reduce tolerance to higher carbohydrate intake during exercise.
Practical application in endurance
In practice, understanding carbohydrate oxidation rate helps optimize nutritional strategies.
Athletes can oxidize around 60 g of carbohydrates per hour from a single source. When combining different carbohydrate sources, this can increase to 90 g per hour or more.
Intake should be distributed throughout the exercise, and strategies should be tested during training, not only on race day.
Factors such as temperature, intensity, and individual characteristics must also be considered.
Conclusion
Carbohydrate oxidation rate depends not only on intake, but on the entire process of digestion, absorption, and muscle utilization.
Intestinal absorption, gastric emptying, training adaptations, and nutritional strategy are key factors in maintaining energy supply during exercise.
For this reason, well-planned and individualized strategies are essential to optimize performance in endurance events.
Reference
Podlogar, T., Wallis, G. A. (2022). New horizons in carbohydrate research and application for endurance athletes. Sports Medicine. Available at: https://link.springer.com/article/10.1007/s40279-022-01757-1
