Other than energy, the next most important nutritional component for athletes is adequate carbohydrate consumption. Carbohydrate is stored in the body as glycogen. Glycogen stores are limited (liver: ~ 80– 100 g and skeletal muscle: 300–400 g) and operate as a main source of fuel for up to a few hours during moderate to high-intensity aerobic exercise (e.g., 65– 85% VO2max). Carbohydrate (as blood glucose and muscle glycogen) has the advantage of generating more ATP per volume of oxygen (O2) compared to fat.
Importantly, as glycogen levels decline, the ability of an athlete to maintain exercise intensity and work output also decreases while rates of tissue breakdown increase. Generally, exhaustion of liver and muscle carbohydrate stores is associated with:
Fatigue
Reduced work
Impaired concentration
That’s why carbohydrates are a crucial component of an athletes’ diet.
The simplest guideline to maximize endogenous glycogen stores is for a high-performance athlete to consume appropriate amounts of carbohydrate. Appropriate amounts are relative to the intensity and volume of training.
Recommendations from the Academy of Nutrition and Dietetics (AND), Dietitians of Canada (DC), the American College of Sports Medicine (ACSM) and International Society of Sports Nutrition (ISSN) are summarized below. For the complete positions and recommendation, you can check the references listed at the end.
The recommendations for carbohydrate consumption for athletes are listed below. Exercise duration is listed within parentheses.
Carbohydrates
Daily requirements
5-7 g/kg/day (1 h/day)
6-10 g/kg/day (1-3 h/day)
8-12 g/kg/day (≥4 h/day)
Pre-exercise
6 g/kg/day (<90 min)
10-12 g/kg/day (>90 min) + 1-4 g/kg (1-4 h prior to event)
During exercise
30-60 g/h (<2,5 h)
60-70 g/h (>2,5 h)
90 g/h (>2,5 h if tolerable)
Post exercise
8-10 g/kg/day (first 24 h)
1-1,2 g/kg/h (first 3-5 h) or 0,8 g/kg/h + protein (0.3 mg/kg/h) or caffeine (3 mg/kg)
It should be noted that athletes often fail to meet recommended amounts of energy and carbohydrate; consequently, personalized strategies to replenish carbohydrate stores are important to prepare for maximal performance in the next competition. In addition, gastrointestinal discomfort is a main issue that the professional dietician should deal with.
References:
Kerksick, C. M., Arent, S., Schoenfeld, B. J., Stout, J. R., Campbell, B., Wilborn, C. D., Taylor, L., Kalman, D., Smith-Ryan, A. E., Kreider, R. B., Willoughby, D., Arciero, P. J., VanDusseldorp, T. A., Ormsbee, M. J., Wildman, R., Greenwood, M., Ziegenfuss, T. N., Aragon, A. A., & Antonio, J. (2017). International society of sports nutrition position stand: nutrient timing. Journal of the International Society of Sports Nutrition, 14, 33. https://doi.org/10.1186/s12970-017-0189-4
Vitale, K., & Getzin, A. (2019). Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. Nutrients, 11(6), 1289. https://doi.org/10.3390/nu11061289