As I’ve described in a
previous article on this site, 60-70 percent of an athlete’s diet should be
comprised of carbohydrate calories where the sport involves repeated bouts of
all-out effort and for long distance events. For these events. For these events
carbohydrate energy represents the predominant energy source for maximum
sustained power. Carbohydrate depletion during these events is known to hasten
the onset of fatigue and to hinder performance capabilities. As a result
athletes should be aware of effective carbohydrate repletion techniques as a
means of optimizing their performance. Prior to exercise a carbohydrate rich
meal should be consumed 3-4 hours before the game or training session. Thirty
minutes prior to exercise 10-20 grams of fructose sugar mixed with 20-25 ounces
of water can also maximize carbohydrate availability and utilization, enhancing
during prolonged exercise events has also been shown to improve performance.
Numerous studies have demonstrated increased exercise time to fatigue, power
output during exercise and improved sprint performance following prolonged
exercise when carbohydrate is ingested during exercise. Carbohydrates ingested
during intensive or prolonged exercise are able to maintain blood sugar more
effectively, thereby providing an immediate source of carbohydrate energy to the
exercising muscle. As a result this strategy spares the rapid breakdown of liver
carbohydrate, which is then able to provide blood sugar for a longer period of
time during the event. Indeed, a recent report has observed a 59% reduction in
liver carbohydrate (glucose) production during prolonged exercise when
carbohydrate is ingested. This strategy enables the liver to deliver
carbohydrate through the bloodstream as blood sugar, thus the exercising muscle
uses up its own carbohydrate stores (glycogen) at a slower rate. Slowing the
depletion rate of muscle carbohydrate stores allows the muscle to work at higher
levels of power for a longer period of time; hence performance improves.
prolonged exercise the muscle breaks down carbohydrates as a source of energy at
a rate of 1-1.5 grams per minute. Based on a number of studies it appears that
athletes need to ingest carbohydrates at a rate that will supply them with
carbohydrates at approximately 1 gram per minute. This can be achieved by the
ingestion of 600 to 1,000 ml/hour of solutions (drinks) containing 6-10%
carbohydrate. This simply means that for every 100 ml water in a sports drink
there should be no more than 6-10 grams of carbohydrate. Any more carbohydrate
than this will slow down the rate of gastric emptying and water absorption into
the bloodstream. Gastric emptying means the rate at which carbohydrates and
fluids pass through the stomach into the small intestine where the maximum
amount of absorption into the bloodstream occurs.
drinks for instance, contain at least 12 grams of carbohydrate per 100 ml of
water and, therefore, are not good sports enhancement beverages.
The popular carbohydrate
sports enhancement drinks in the marketplace all meet the 6-10% carbohydrate
criteria as I have explained it.
As for the type of
carbohydrate that is best to include in a sports enhancement drink during
competition, there is little difference between maltodextrines (glucose
polymers) glucose and sucrose in their metabolic and performance effects during
exercise. However, maltodextrin
solutions tend to be less sweet, and therefore more palatable, than solutions of
only simple sugars. In contrast, fructose ingestion during prolonged exercise
does not improve performance. Fructose is the beverage of choice 30 minutes
prior to exercise, but not during exercise.
As a general guide as to how
to practically apply this information, let me summarize this information in the
following way. During a strenuous
exercise event that will last for more than 60 minutes, consider drinking 5-8
ounces of a carbohydrate based sports enhancement drink every 10 – 15 minutes. This will not only provide the right concentration and type
of carbohydrates to stave off carbohydrate depletion your liver, bloodstream and
exercising muscles, but also provides an optimal strategy to prevent
dehydration. Most of these drinks
(i.e. Gatorade) also provide sufficient sodium and/or potassium to prevent
hyponatremia which is a loss of sufficient sodium (from sweating) to result in a
life-threatening condition involving brain swelling and other complications.
As a rule usually a minimum of 3 to 4 hours of continuous sweating is
required to develop hyponatremia, but it remains a nutritional concern for
certain types of sporting events.
In conclusion the use of
carbohydrate sports drinks is a proven method to enhance athletic performance in
events lasting at least 60-90 minutes, which requires repeated bouts of
explosive power and in long distance events where maintaining optimal speed is
critical to the outcome. Consuming
5-8 ounces of these drinks every 10-15 minutes is the best way to deliver the
optimal amount of carbohydrate to the exercising muscle during intense and
prolonged activity. By the way, colder fluids are absorbed faster than fluids at
room temperature. Thus, colder
beverages are a better choice for optimal carbohydrate and fluid replenishment.
Copyright 1998 Dr. James
Meschino D.C., M.S.
Costill DL, and Hargreaves M.
Carbohydrates nutrition and fatigue. Sports medicine 1992; 13; 2:86-92.
O, Sahlin K, Hagenfeldt L, Wahren J. Influence of glucose and fructose ingestion
on the capacity of long term exercise in well trained men. Clinical Physiology
4: 483-494, 1984.
AR, Coyle EF. Reversal of fatigue during prolonged exercise by carbohydrate
infusion or ingestion. Journal of Applied Physiology 63: 2388-2395, 1987.
AR, Coyle EF. Effect of carbohydrate feedings during high-intensity exercise.
Journal of Applied Physiology 65: 1703-1709, 1988.
AR, Coyle EF. Metabolism and performing following carbohydrate ingestion late in
exercise. Medicine and Science in Sports and Exercise 21: 59-65, 1989.
Coyle EF, Coggan AR, Hemmet MK, Ivy JL. Muscle glycogen utilization during prolonged
strenuous exercise when fed carbohydrate. Journal of Applied Physiology 59:
Coyle EF, Hagberg JM, Hurley BF, Martin WH, Eshani AA et al. Carbohydrate feeding
during prolonged strenuous exercise can delay fatigue. Journal of Applied
Physiology 55: 230-235, 1983.
M, Costill DL, Coggan A, Fink WJ, Nishibata I. Effect of carbohydrate feedings
on muscle glycogen utilization and exercise performance. Medicine and Science in
Sports and Exercise 16: 219-222, 1984.
Ivy JL, Katz AL, Cutler CL, Sherman WM, Coyle EF, Muscle glycogen synthesis after
exercise; effect of time of carbohydrate ingestion. Journal of Applied
Physiology 64: 1480-1485, 1988a.
Ivy JL, Lee MC, Broznick JT, Reed MJ. Muscle glycogen storage after different
amounts of carbohydrate. Journal of Applied Physiology 65: 2018-2023, 1988b.
JB, Costill DL, Houmard JA, Fink WJ, Pascoe DD et al. Influence of carbohydrate
dosage on exercise performance and glycogen metabolism. Journal of Applied
Physiology 67: 1843-1849, 1898a.
R, Paul GL, Seifert JG, Eddy DE, Halaby GA. The effect of glucose, fructose and
sucrose ingestion during exercise. Medicine and Science in Sports and Exercise
21: 275-282, 1989.