By PCG Nutritionist Namrita Kumar
Energy to fuel endurance exercise mainly comes from carbohydrate and fat sources. As intensity increases during endurance exercise, fuel oxidation crosses over from predominantly fat oxidation to a higher percentage of carbohydrate oxidation.
By implementing sound training and nutrition practices, physiological adaptations over time should result in higher fat oxidation at a higher percentage of maximal aerobic capacity; BUT, carbohydrate remains an essential and important energy source when the goal is to complete a distance as quickly as possible, (e.g. in a bike race)!
Stored glycogen (endogenous carbohydrate) and carbohydrate supplements (exogenous carbohydrate) are the primary source for carbohydrate oxidation to sustain higher intensity performance during a competition. If glycogen stores are relatively full going into a race and the event is < 60 minutes long, little to no carbohydrate intake is required during the event itself. There is evidence that even rinsing carbohydrate in the mouth (without ingesting) may improve performance when the body does not have to rely on exogenous carbohydrate supplementation to meet the demands of the race.
If the event is between 1-2 hours in duration, it's a good idea to supplement with ~30 to 60 grams of carbohydrate per hour (120-240 calories per hour). When approaching ingestion rates of ~60 grams carbohydrate per hour, it's best to use a blend of carbohydrate sources such as glucose-fructose or maltodextrin-fructose to reduce the likelihood of GI distress during the race. Also, include plenty of training sessions to adapt the GI tract to ingesting this rate of carbohydrate intake at race intensity.
If the event is longer than 2.5 to 3 hours, carbohydrate blends of ~90-110 grams per hour (360-440 calories per hour) can be beneficial to performance. A carbohydrate blend is essential at this high rate of intake, as is training the GI tract to process the rate of carbohydrate ingestion at race intensity.
The longer the race and the lower the intensity of race pace, the more solid food (low-fat, low-fiber) may be introduced into a race fueling plan.