Even with the right genetic make-up and best training programme, making sure you have the right carbohydrate intake and hydration strategy is crucial for successful race performance.
The body stores energy from carbohydrate in the form of glycogen in muscles and the liver. Muscle glycogen is a readily available energy source for exercising muscles. Liver glycogen is essential in helping maintain blood sugar (glucose) levels, as ensuring a constant supply of glucose prevents effects associated with hypoglycaemia (low blood sugar level) i.e. shakiness, anxiety and reduced concentration.
Once these glycogen stores become depleted, exercise at maximal intensities cannot be maintained. That’s why the body must be supplied periodically with carbohydrates in the right form and at sufficient rates during a prolonged intense endurance session.
"How" does carbohydrate intake during exercise improve performance?
The reasons why carbohydrate intake can improve performance during exercise are very complex. But the two major mechanisms are:
- The function as an energy supplier by maintaining blood glucose concentration and high rates of carbohydrate oxidation when glycogen levels in muscles and liver are low.
- The impact on the brain: for exercise sessions lasting less than an hour, the body’s glycogen stores are not a performance-limiting factor. However, recent research has shown that carbohydrates can improve performance even in those sessions – even without actual ingestion. Simply rinsing the mouth for a few seconds with a beverage containing carbohydrates activates specific receptors in the oral mucous membranes. This stimulates the central nervous system in the brain, which can cause a performance-enhancing effect.
Carbohydrate requirements during competition events
The current recommendations for the optimum carbohydrate intake quantity during competition, based on numerous studies and the IOC Consensus Statement on Sports Nutrition 2010, are listed in the table below:
If glucose alone is provided as the carbohydrate source during exercise, the energy oxidation from carbohydrates is limited to approximately 60 grams per hour. Ingestion of different sources of carbohydrates as for example in C2MAX, can allow more than 60 grams of carbohydrate to be used per hour as a source of energy. Scientific research has shown this special 2:1 ratio of glucose and fructose can supply exercising muscles with more energy for a given time compared to glucose alone and this can lead to an improvement in prolonged exercise performance.
Sebastian Kienle, reigning IRONMAN World Champion, speaks from experience: "The amount of carbohydrates that you take on during the cycle and run can often decide the result of the race." It is important to remember that the highest tolerated carbohydrate intake (in grams per hour) differs widely from person to person. However, it is possible to ‘train’ the gut to adapt to higher amounts of carbohydrate. Tips for targeted preparation for competition: Gradually increase the quantity of carbohydrate intake (in an ideal ratio of sugars) with sports drinks, gels or bars over several days during the training phase before the competition. In the words of Sebastian Kienle, "test your way to your individual maximum and to your personal best strategy".
Conclusion: The optimal amount of carbohydrate intake during competition highly depends on the duration and intensity of the exercise, but must also be tailored according to athlete’s individual tolerance. Train and practise your carbohydrate strategy during training and never try out something new in competition!
© Corinne Mäder Reinhard, Senior EU Sports Nutrition Manager PowerBar. International Olympic Committee post-graduate Diploma in Sports Nutrition
- Burke, L.M, Hawley, J. A, Wong, & S.H, Jeukendrup, A.E. (2011). Carbohydrates for training and competition. J Sports Sci, 29 Suppl 1:S17-27.
- Currell, K. & Jeukendrup, A.E. (2008): Superior endurance performance with ingestion of multiple transportable carbohydrates; Med Sci Sports Exerc, 40:275–281.
- Jeukendrup, A. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med, 44 Suppl 1:S25-33.
- Jeukendrup, A. E. (2011). Nutrition for endurance sports: marathon, triathlon, and road cycling. J Sports Sci, 29 Suppl 1:S91-9.
- Stellingwerff, T., & Cox, G.R. (2014). Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations. Appl Physiol Nutr Metab, 39(9):998-1011.