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Does carbohydrate loading really "load" on success?



Callie Wade

October 10, 2008


IHSA Girls Cross Country meet, October 2008




In an attempt to sharpen their “competitive edge,” athletes in all sports experiment with various techniques to enhance their performances. In addition to hours of practicing and strategizing each day, trainers, coaches, and competitors alike realize that daily food intake has a major impact on athlete’s success. Diet is particularly important for long distance runners who must sustain high energy levels for long periods of time. This is why distance runners experiment with different regimes, trying to find which one augments performance the most. Many athletes practice “carbohydrate loading” prior to a race. Cross country teams have turned this practice into a tradition of “pasta parties” the night before the race where the whole team gathers to “load” up on carbohydrates in the form of pastas and breads. While this is a great bonding experience for the team and fun for all, does the ingestion of carbohydrates really improve the runner’s performance in the race the next day? Does carbohydrate loading really “load” on success?


What are carbohydrates? What is carb-loading?


            Carbohydrates, most commonly found in pastas, breads, grains, and rice as well as fruits and vegetables are your body’s primary source of energy,” writes the Mayo Clinic, a non-profit group medical practice that strives to provide health services and information to the public. When a person ingests a carbohydrate, the body breaks it down into sugar which moves to the bloodstream and is also “stored in the muscles and liver as glycogen,” (Mayo Clinic). This glycogen in the muscles and blood stream is the body’s fuel for training and competing, as well as everyday activities ( The concentration of glycogen in the muscles depends on the percentage of carbohydrates in a person’s diet, and their training level reports Clyde Williams of the Department of Physical Education, Sports Science and Recreation Management at Loughborough University in the UK (1993). Furthermore, adds Marilyn S. Peterson, author of Eat to compete: a guide to sports nutrition, “athletes with well developed muscles will be able to store more glycogen,” (1996, p. 219).

Glycogen levels in an athlete’s muscles fluctuate during periods of training and rest (Applegate, 1997). Prior to a training session, the glycogen levels in an athlete's muscles are relatively high. Then, as the athlete trains, those stores of glycogen are used to fuel the training and are depleted; the resulting very low glycogen levels cause fatigue (Peterson, 1996). However, original glycogen levels are achieved again, through consumption of more carbohydrates. Carbohydrate-loading attempts increase the muscle’s glycogen storage so as to increase the amount of available energy for competition (Williams, 1993).

Text Box: The Journal of Nutrition, 1997Text Box:  In the past, carbohydrate loading required training to exhaustion in order to deplete the glycogen storage in the muscles, followed by three days of a low carbohydrate diet. Then, the athlete would consume a high carbohydrate diet for the three days leading up to the competition (Williams, 1993). The idea was that by extremely depleting the glycogen in the muscles for three days, when the athlete did return to eating carbs, he or she could store more glycogen, hence, collecting more fuel for the event.

However, as with any extreme diet regime, there were some potential side effects. Many times, athletes practicing this traditional carb-loading gained water weight because water is retained in the muscles with the carbohydrates (Peterson, 1996). Additionally, many athletes who over-loaded experienced flatulence and loose stools (May Clinic, 2006). Others found that their abdomen distended due to the increase in fiber ingestion (Peterson, 1996). These side effects as well as general discomfort during the low –carb days resulted in the fading out of the traditional practice fading out (Mayo Clinic, 2006).

Running Times

Now, most athletes practice “a modified method which is safer and equally effective at increasing muscle glycogen. The most important factor influencing glycogen storage stores is to consume 50-60% of calories from carbohydrates on a daily basis,” writes The Health Central Network, an organization that acts as a central location for health information on the wed ( Rather than manipulating their systems to deplete and then over-restore carbohydrates, this new method ensures that the muscle glycogen concentrations are consistently high (Peterson, 1996). But does this practice really enhance athlete performance?


What do the studies show? The experts are finding…

The first scholars to delve into the effects of carbohydrate loading on athletic endurance were Jan Karlsson and Bengt Saltin of the Department of Physiology at Gymbastik – och Idrottshogskolan, in Stockholm Sweden. In 1971, they asked the question as to whether or not high muscle glycogen levels prior to exercise improve “running speed as well as endurance capacity” (Williams, 1996, p. 46). The researchers took two groups of subjects, both of which ran a 30 km cross-country race. The first group followed a carbohydrate-loading diet while the other ate a normal, mixed diet prior to the race. Then, three weeks later they reversed the roles and group one ran the race after following a normal, mixed diet while group two practiced carbohydrate loading. The results showed that the high carbohydrate diet did not improve the runner’s speed at the beginning of the race, but rather allowed him or her to “maintain an optimum pace longer,” (Williams, 1996, p. 46).  Regardless, “the best performance (shortest work time), which was between 114 and 163 minutes, was obtained by all subjects in the race preceded by the special diet,” (Karlsson et al. 1971, p. 203). Also, this study showed that the runners’ muscle glycogen levels were depleted after the race at the exhaustion point. Finally, the researchers concluded, “that the enhanced capacity for prolonged exercise after a carbohydrate-enriched diet was due to an increase in muscle glycogen stores,” (Karlsson et al. 1971, p. 203).

Text Box: Journal of Applied PhysiologyLater, in 1988, J. Brewer, C. Williams, and A. Patton published a study in the European Journal of Applied Physiology that demonstrated positive results on performance from the practice of carbohydrate loading. This study took 30 runners, broke them up into three groups, and had each group run on a level treadmill at about 70% of their peak oxygen consumption (VO2) until exhaustion, after having eaten their normal, mixed diet (Brewer et al., 1988). Then, after supplementing their diets with protein, complex carbohydrates, or simple carbohydrates, the groups repeated the run. The results showed that the running times from the first run to the second for the complex carbohydrate group improved by 26% and by 23% for the simple carbohydrate group (Brewer et al., 1988). In contrast, the running times of the control group did not improve after their diet had been supplemented with protein and fat. The results of this study allowed for two conclusions. First, that carbohydrate loading did indeed improve performance times. Secondly, it showed that “supplementing normal diets with simple carbohydrates, such as confectionery products, is as effective in restoring muscle glycogen as are complex carbohydrates (Williams, 1993, p. 45).

However, not all study results have been so supportive of carbohydrate loading. In 1990 several researchers in Denmark, headed by Klavs Madsen, collaborated on a study similar to the one above, to test the effect that carbohydrate loading has on endurance running capacity (Madsen et. al, 1990). In this study, three female and three male well-trained runners ran on a level treadmill until exhaustion after eating their normal mixed diets. Then the researchers increased their muscle glycogen concentrations by 25% through consumption of carbohydrates and again had them run on a level treadmill until exhaustion. Time to exhaustion for the first trial was 70 minutes and 77 minutes for the second trial. This 10% increase in times is not significant enough to conclude that the carbohydrate loading had a great impact on the runners’ performance (Willimas, 1993). Also, when the researchers measured the average muscle glycogen levels in the runners after both trials, the values were not low enough to be the cause of fatigue; both trials resulted in approximately 25% decrease in muscle glycogen concentration. One possible flaw of this study was that runner’s maximum performance could have been prohibited by the catheters and biopsies used to obtain the necessary data. Finally, this study concluded that running does not deplete muscle glycogen levels as much as other sports, for example, cycling, and that carbohydrate loading does not appear to improve the endurance capacity of distance runners (Madsen et al., 1990, Williams, 1993).

Then in 1992 William M. Sherman, J. Andrew Doyle, David R. Lamb, and Richard H. Strauss of Ohio State University in Columbus, Ohio, performed another study on the effects of carbohydrate diets on “muscle glycogen and performance in runners and cyclists,” (Sherman et al., 1992, p. 27). This study took thirty-six volunteer subjects and had them participate in seven consecutive days of training sessions while maintaining either a high carbohydrate diet or a moderate carbohydrate diet. The training sessions included exercise for one hour at 75% peak oxygen consumption (VO2) and five, one-minute sprints (Sherman et. al, 1992). Then, on the seventh day, the subjects cycled or ran to exhaustion at 80% peak oxygen consumption. The results showed that those following the high carbohydrate diet maintained their muscle glycogen levels until the end and that the muscle glycogen levels of those following the moderate carbohydrate diet fell by about 30-36% (Sherman et al., 1992). However, all the subjects completed the training sessions and there were no differences in times. These results support the idea that high carbohydrate diets allow the muscles to sustain glycogen levels throughout training but do not connect these high levels to enhanced performance.


What does this mean for me? What this means for you…

            As shown in the above sampling of studies, there has been much research into this issue of the effects of carbohydrate loading on athletic endurance. Karlsson and Saltin and Brewer et al.’s findings lead us to believe that carbohydrate loading greatly enhances endurance performance while the evidence of Madsen et al. and Sherman et al. shows otherwise. Nevertheless, one fundamental idea that all of the above researchers agree on is that carbohydrate consumption increases the stores of glycogen in the muscles and that carbohydrates are the body’s main source of energy for physical activity. From there they disagree on whether or not higher levels of muscle glycogen concentration  lead to enhanced running performance. Ultimately, “more research specifically related to running needs to be conducted to confirm the results of these studies,” (Hawley et al, 2000, p. 557).

Text Box: Road RaceHowever, some conclusions can be drawn from these ambiguous results. Runners can conclude that moderate to high carbohydrate consumption is necessary during training to replenish glycogen in the muscles. Regardless of whether or not it sharpens their “competitive edge,” researchers do know that glycogen is depleted during training and carbohydrate consumption can replenish that (Williams, 1996). Also, rather than make generalizations about carbohydrate loading, individual runners need to experiment with what works for them as a competitor, until researchers discover more definitive answers, keeping in mind the potential side effects of “overloading” on carbohydrates, discussed earlier.

Thus, although the experts have mixed reviews about the effectiveness of carbohydrate loading on running performance, moderate to high carbohydrate consumption during training and prior to race day will assure that glycogen levels in the muscles are high and ready to provide fuel for the race if indeed that does enhance performance. Hence, in a way, the “pasta party” tradition is just that, a tradition; however, regardless of if the runner believes that it will help them to shave off an extra minute or two in their race, it is a great way for teams to replenish their muscle glycogen together.



Literature Cited


Brewer, J., Williams, C., & Patton, A. (1988). The influence of high carbohydrate diets on endurance running performance. European Journal of Applied Physiology, 57, 698-706. Retrieved October 8, 2008, from Google Scholar.


Hawley, J. A., Schabort, E. J., & Noakes, T.D. (2000). Distance Running. In R. J. Maughan (Ed.), Encyclopedia of Sports Medicine (Vol. 7, pp. 550-561). Oxford: Blackwell Science Ltd.


The HealthCentral Network (2005). Nutrition recommendations for athletic performance. Retrieved October 3, 2008, from


Karlsson, J., & Bengt, S. (1971). Diet, muscle glycogen, and endurance performance. Journal of Applied Physiology, 31(2), 203-206. Retrieved October 8, 2008, from Google Scholar.


Madsen, K., Pedersen, P. K., Rose, P., Richter, E. A. (1990). Carbohydrate supercompensation and muscle glycogen utilization during exhaustive running in highly trained athletes. European Journal of Applied Physiology, 61, 467-472. Retrieved October 8, 2008, from Google Scholar.


Mayo Clinic (2006). Carbohydrate loading: can your diet boost your athletic performance?. Retrieved October 3, 2008, from


Peterson, Marilyn S. (1996). Eat to compete: a guide to sports nutrition. St. Louis: Mosby.


Sherman, W. M., Doyle, J. A., Lamb, D. R., & Strauss, R. H. (1992). Dietary carbohydrate, muscle glycogen, and exercise performance during 7 d of training. The American Journal of Clinical Nutrition, 57, 27-31. Retrieved October 7, 2008, from Google Scholar.


Williams, C. (1993). Carbohydrate needs of elite athletes. In A.P. Simopoulos & K.N. Pavlou (Eds.), Nutrition and Fitness for Athletes. World Review of Nutrition and Dietetics (vol. 71, pp 34-60). Basel: Karger.




The Journal of Nutrition: Applegate, E.A., & Grivetti, L.E. (1997). Search for the competitive edge: a history of dietary fads and supplements. The Journal of Nutrition. Retrieved October 8, 2008, from Google Scholar.


IHSA Girls Cross Country 2008:





Journal of Applied Physiology:


Road Race:


Running Times:




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