Andrew Jagim Ph.D, CSCS
Runners, cyclists, and other endurance athletes are constantly looking for ways to improve their performance. A commonly used strategy is the use of nutritional supplements to “boost” energy and enable them to perform longer and or harder before fatigue sets in. The majority of energy used during endurance events is derived from carbohydrates. Carbohydrates can be stored in the liver and skeletal muscle as glycogen. When exercise lasts longer than 60 minutes, glycogen stores begin to deplete. Without the number one supplier of energy during exercise, fatigue will soon follow. An easy way to help maintain carbohydrate levels, slow down the rate of glycogen depletion and aid in performance is to consume a carbohydrate/electrolyte solution. Ideally this beverage should be a 4-8% carbohydrate solution, with an ideal consumption rate of 8-12 oz every 10-15 min (around 30-60 grams of carbohydrates total). This should help maintain carbohydrate levels within the body and help delay the onset of fatigue. The most common food sources of carbohydrates used typically include: sports beverages, crackers, bananas, carbohydrate gels, and bread. Regardless of which type of carbohydrate used, the main goal is to help supplement the body with additional sources of energy during exercise. 
Another important and often overlooked ergogenic aid during endurance events is water. During exercise in the heat, sweat rates of up to 1.5-2 L/hr have been reported. This can quickly lead to dehydration and ultimately a drop in performance. Every 1% of your body weight lost as sweat results in an increased heart rate of 7 beats per minute, which can put additional stress on the cardiovascular system during exercise. It’s been estimated that a 4% loss can result in a 48% decrease in endurance capacity. Therefore the number one priority during long distance events (especially in the heat) should be hydration.
A number of studies have also shown that caffeine ingestion can significantly improve endurance capacity as well. Caffeine ingestion can increase fat mobilization (up to 18%) in the blood and allow it to be burned as fuel. This allows carbohydrate stores to last longer and essentially “spare glucose” which can also delay the onset of fatigue. Studies have shown increases of up to 20% in performance following the ingestion of caffeine. Doses of 3 to 9 mg per kg of bodyweight or a total of 250mg have been shown to be the most effective.
For additional information:
- Ivy, J., Costill, D., Fink, W., & Lower, R. (1979). Influence of caffeine and carbohydrate feedings on endurance performance. Med Sci Sports. 11(19), 6-11. http://www.ncbi.nlm.nih.gov/pubmed/481158
- Kreider, R., Leutholtz, B., Katch, F., & Katch, V. (2009). Exercise & Sport Nutrition. Nutrient Timing. p. 93-120.