An athlete in heavy endurance training should maintain a daily carbohydrate intake that is approximately what percentage of his/her total energy intake?

30% carbohydrate intake is characteristic of low-carbohydrate dietary patterns suited for sedentary or low-activity lifestyles, not heavy endurance training demands.

55% carbohydrate intake may be adequate for moderate recreational activity but falls below the 60-70% range recommended for athletes in heavy endurance training.

Heavy endurance training rapidly depletes muscle and liver glycogen, requiring approximately 60-70% of total energy intake from carbohydrates to support training and recovery. A value of 65% falls squarely within this recommended range and reflects ACSM and sports nutrition guidelines for high-volume endurance athletes. Adequate carbohydrate intake at this level helps prevent glycogen depletion, reduce fatigue, and support adaptation.

85% carbohydrate intake is excessively high and would leave insufficient caloric proportion for adequate dietary fat and protein, impairing recovery and hormonal function.