INDIANAPOLIS — The American College of Sports Medicine (ACSM) has released a study that provides new information about the well-known technique of carbohydrate loading for improved performance. The results were published in the June 2002 issue of Medicine & Science in Sports & Exercise(r). Based on the familiar carbohydrate-loading regimen of two to six days of reduced-intensity exercise and high-carbohydrate consumption for attainment of high muscle glycogen levels, and on the knowledge that the rates of glycogen synthesis are very high during recovery from maximal intensity exercise, the present study sought to determine whether combining a short bout of high-intensity exercise with one day of high carbohydrate intake would result in the same or similar muscle glycogen levels. Athletes could then achieve carbohydrate loading for performance more quickly, without the deconditioning that often accompanies the classic two-to-six day regimen.

"There is evidence that carbohydrate loading increases endurance and performance because of high glycogen levels," said Paul A. Fournier, Ph.D., from the Department of Human Movement and Exercise Science at the University of Western Australia. Fournier, lead researcher on the study, said "Athletes who don't want to disrupt their normal training protocol are at a disadvantage, and we saw the need to develop a carbohydrate-loading regimen that would facilitate high glycogen levels within a shorter time period."

To determine whether a one-day high-carbohydrate intake after a short bout of high-intensity exercise would lead to the attainment of these high glycogen levels, the researchers designed a study that started with seven endurance-trained men, the average age of whom was 22 years. After dietary analysis, they were trained on an appropriate exercise protocol, carbohydrate supplementation, and the exercise equipment to be used. After muscle biopsy for a baseline, the subjects performed sprint cycling at 130 percent of VO₂ peak. The subjects then ingested 12 grams per kilogram of lean body weight over the next 24 hours, including maltodextrose-enriched beverages.

The researchers' histochemical and biochemical analyses indicated a large increase in plasma lactate levels as a result of the high intensity exercise, followed by a large increase in muscle glycogen stores caused by the ingestion of carbohydrates. Overall, a relative increase of 82 percent took place, and all types of muscle fiber were involved. The researchers concluded that their study showed for the first time that it is possible to accumulate supranormal muscle glycogen levels within only 24 hours by feeding athletes concentrated carbohydrates after a three-minute bout of high-intensity exercise.

In addition to the fact that the subjects were exercise-trained, the researchers note several mechanisms that may explain the high initial rates of muscle glycogen synthesis. A transient rise in blood glucose and insulin levels usually accompanies early recovery from high-intensity exercise; the body also resynthesizes significant amounts of glycogen from high lactate levels at this stage of the recovery period; and the regulation of two enzymes known as glycogen synthase and glycogen phosphorylase. It also remains to be seen in further study whether the high rate of glycogen depositon occurs throughout the 24 hours following the exercise bout or are restricted mainly to the first few hours. The regimen described is, however, an improvement over the two-to-six day regimen, if only because it will be easier to maintain and thus lead to improved athletic endurance and performance.

The American College of Sports Medicine is the largest sports medicine and exercise science organization in the world. More than 18,000 International, National and Regional members are dedicated to promoting and integrating scientific research, education and practical applications of sports medicine and exercise science to maintain and enhance physical performance, fitness, health and quality of life.

NOTE: Medicine & Science in Sports & Exercise(r) is the official journal of the American College of Sports Medicine, and is available from Lippincott, Williams & Wilkins at 1-800-638-6423. For a complete copy of the research paper (Vol. 34, No. 6, pages 980-986) or to speak with a leading sports medicine expert on the topic, contact the Department of Communications and Public Information at 317-637-9200. Visit ACSM online at www.acsm.org.

The conclusions outlined in this news release are those of the researchers only, and should not be construed as an official statement of the American College of Sports Medicine.

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