How Protein Builds Carbohydrate Stores & Aids Muscle Recovery
by Edmund R. Burke, PhD
It is well known in the running community that adequate glycogen stores are important for optimizing performance during an extended workout. Research has shown that muscle glycogen stores can decline on consecutive days of training if one does not pay attention to post-exercise carbohydrate and protein consumption. Consequently, adequate glycogen stores are essential not only for optimizing performance during competition, but also for maintaining the quality of training.
Athletes, who wait more than two hours to consume carbohydrates, restore about 50 percent less muscle glycogen than those who consumed carbohydrates during the two-hour period. The difference relates to insulin, a hormone released by the pancreas that is essential for the manufacture of muscle glycogen. Not surprisingly, researchers have focused on enhancing insulin release during recovery. Increasing carbohydrate consumption is one way to stimulate insulin, but the effect of carbohydrate on glycogen storage reaches a plateau.
John Ivy, Ph.D. from the University of Texas and L. J. C. van Loon, Ph.D. from the University of Maastricht, the Netherlands, have shown that protein when combined with carbohydrate almost doubles the insulin response. The ideal ratio of carbohydrate to protein is 4:1 (four grams of carbohydrate to one gram of protein.) This is also a case where more is less. Too much protein (fat has a similar effect) taken in the 0-2 hour post-exercise period slows rehydration and glycogen replenishment. A 4:1 ratio which I call the Optimum Recovery Ratio, or OR2 delivers the benefits of protein without having a negative effect on rehydration.
In the Maastricht University study cyclists depleted their glycogen stores during a vigorous, high intensity cycling workout on three occasions. They refueled with either a placebo, carbohydrate or carbohydrate and protein drink. The researchers then performed a muscle biopsy. Those athletes who took the carbohydrate and protein mix had 100 percent greater stores than those who only drank the carbohydrate. Insulin was also highest in those who consumed the carbohydrate and protein drink.
Recently Dr. Ivy completed a study on a sports drink which contains carbohydrate and protein in a 4 to 1 ratio as well as the amino acid arginine. This study will be presented at the American College of Sports Medicine national meeting. Dr. Ivy found that the drink, Endurox R4, compared to a conventional rehydration drink, increased plasma glucose levels by 17 percent and produced a 92 percent greater insulin response. Most impressively, there was almost a two-fold increase in muscle glycogen storage levels. This study may explain previous reports that Endurox R4 increased exercise performance by 55% in subsequent exercise bouts when compared to a conventional rehydration drink.
Another important nutritive factor in the protein equation is the amino acid arginine. In research published in the International Journal of Sports Nutrition, Drs. Ben Yaspelkis and John Ivy, have shown carbohydrate-arginine supplementation increased muscle-glycogen replenishment by 35 percent more than carbohydrate alone. Arginine, when added to carbohydrate, makes more glucose available for glycogen production by increasing the use of fat, rather than glucose, as an energy source after exercise. Simply put, arginine makes glycogen replenishment more efficient.
This research clearly shows that protein can enhance muscle glycogen replenishment but that is just one part of the protein story. Protein provides amino acids, such as glutamine, necessary to rebuild muscle broken down as a consequence of exercise. For example, at the end of an intense training session the catabolic hormone, cortisol, rises. Cortisol increases muscle protein breakdown. Consuming a carbohydrate/protein drink that contains glutamine immediately after a workout or race can blunt this rise in cortisol thereby reducing protein breakdown. Glutamine is also important for fueling the immune system. Low glutamine stores can suppress the immune system, making you more susceptible to colds and other infections during periods of hard training and competition.
Here's another bit of information that supports the use of a carbohydrate- and protein-containing post-workout drink: amino acids and dipeptides (found in whey protein) significantly increase the absorption of water from the intestines. Therefore, putting protein in your post-workout supplement may not only help replenish glycogen stores, it may also help rehydrate your muscles!
The results of these studies are meaningful for any runner who wants to maintain muscle glycogen stores and protect their muscles and immune system from damage. Protein, especially when consumed in the correct proportion with carbohydrate, is an essential nutritive component in speeding recovery following exercise. Compared to solid foods, a carbohydrate and protein combination drink will also empty quicker from the stomach and help rehydrate the body more effectively. The result - improved running performance on your next workout.
Dr. Edmund Burke is a Professor of Exercise Science at the University of Colorado at Colorado Springs, and author of Optimal Muscle Recovery (Avery Publishing 1999).