Specifics of carbohydrate metabolism under sport-specific aerobic workloads

Dr.Biol., Professor O.V. Dobrovolsky1
Dr.Med., Professor E.E. Achkasov1
Dr.Med., Professor M. Bernardi2
Y.S. Romanenkova1
E.K. Kochetkova1
1I.M. Sechenov First Moscow State Medical University under Ministry of Health of Russia (Sechenov University), Moscow
2University of Rome La Sapienza, Rome, Italy

Keywords: carbohydrate barrier, carb-up, glycogen, athlete, muscles.


Introduction. It is known that the glycogen level rise results in an increase of its reserves in the muscles and higher endurance in long-distance running sports. In the meantime, as proved by recent studies one should avoid an extreme carbohydrate diet [2].The two main energy sources during muscle activity are fats (triglycerides) and carbohydrates (glycogen and glucose) accumulated in the body. The ratio between oxidizable carbohydrates and fats is determined by the aerobic power rate: the higher the relative work power, the more efficient the production of energy by oxidizable carbohydrates and, accordingly, the smaller the energy contribution of oxidizable fats to the total energy supply of the working muscles [3].

Objective of the study was to analyze the most effective and presently popular diets prioritizing carbohydrate loading (carb-up).

Results and discussion. The theoretical analysis revealed the most effective carbohydrate nutrition practices.

  • Olboard Method is based on hard high-intensity pre-competitive training, during which glycogen stores are depleted. Then follows a 2-5-day low-carb diet. After this, carbohydrate intake increases significantly – up to 70-85% of total callorage, sometimes up to 600g of carbohydrates, for 1-2 days only to achieve glycogen supercompensation.

According to the modern approach to carb-up, athletes need to reduce the amount of consumed carbohydrates gradually - to the level of 45-65% within 2-3 weeks preceding the competitions. The last 72 hours before the competitions is a carb-up stage, during which the amount of consumed carbohydrates increases by approximately 25%, or to the level equivalent to 8-12 g of carbohydrates per 1 kg of the athlete's weight [10].

In order to consume such a large amount of carbohydrates during the day, an athlete needs to make it a rule to eat high-carb foods, which is scarcely convenient and feasible. It is Gatorade (a mixture of glucose and sucrose in water at a 6% solution) that became the first sports nutrition product. It was created by a team of scientists at the University of Florida and is considered the product that laid the foundation of the global sports nutrition market: energy gels, energy chewing gums and energy bars [6].

  •  Taper’s High Carbohydrate Intake method. The so-called "Taper" (by the name of a French doctor who was the first to suggest this diet) or CSM (carbohydrate saturation method), which provides for certain dietary and training restrictions during preparation for competitions, became widespread as a physical means to improve working capacity half a century ago. In 1981, S. Brown and D. Graham cited the Olympic champion in marathon running F. Shorter, who believed that this method would help improve the competitive result by approximately 3 minutes [1].

The researchers also found that only a small part of athletes consciously measure out carbohydrates in doses. It turned out that around 60% of athletes eat high-protein food before the competitions [8].

Total carbohydrate nutrition is based on the classical studies conducted in the 70s with the use of biopsy aimed to measure muscle glycogen and the ratio between its reserves and the type of nutrition, as well as duration of physical work [11].

  • "Fat Adaptation" concept. Trained athletes keep a low-carb, high-fat diet for up to 2 weeks during their regular training, and start to restore carbohydrates straight after (by taking a high-carb diet, gradually reducing it within 1-3 days before significant competitions). As opposed to an isoenergy carbohydrate diet, this "periodic dieting" protocol contributes to an increases of the fat oxidation rate in the body and muscles for the same time interval, while reducing the muscle glycogenolysis rate during submaximal exercise. It should be noted that these metabolic shifts, that facilitate fat oxidation, retain even in terms of recovery by means of endogenous carbohydrate stores and their increased exogenous availability [5].

The precise time period for optimal fat uptake and carbohydrate rebalancing is not yet determined and may vary for different athletes. It may take time to identify the optimal scheme for each athlete [9].

Glucose compensation during endurance exercises is a widely accepted measure to help athletes, if used correctly, but there is a risk of dehydration or insulin response if too much undigested glycogen is released. Since liquid carbs are absorbed faster, they can prevent the insulin response and, thus, arriving carbohydrates are converted into glycogen more rapidly [6].

It is often suggested in literature that carbohydrate nutrition is dangerous. Based on the study of individual cases, there have arisen concerns about possible cardiac arrhythmias, an increase in the blood serum triglyceride content and muscle fiber braking due to excessive glycogen level [7].

According to Costill D.L. et al., none of these fears has ever been confirmed. Moreover, the long-term monitoring of the functional state of people diagnosed with excessive glycogen content has not revealed any problems of this kind. Therefore, to determine the possibility of damage to the muscle tissue or other risks, it is necessary to conduct a follow-up study [4].

Conclusion. Despite the lack of researches indicating beneficial effects of carbohydrate nutrition on athletes involved in sports where continuous (1-2 hours) physical effort is required, it has also become popular among athletes in more intensive sport disciplines of shorter duration such as football, hockey, and middle-distance running. Many authors believe that glycogen supercompensation extends its normal stock, though this has not been proven yet.


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Corresponding author: dobol@mail.ru


It is known that the glycogen level rise results in an increase of its reserves in the muscles and higher endurance in long-distance running sports. In the meantime, as proved by recent studies an extreme carbohydrate diet should be avoided. The present study analyzes the available literature on the issues of carbohydrate diets in long-distance running sports; and considers the role of carbohydrate barrier for competitive progress in sports. The study makes a special emphasis on the most effective and presently popular diets prioritizing carbohydrate loading (carb-up) including classical carbohydrate systems, Taper’s High Carbohydrate Intake method, Olboard method etc., with a detailed analysis of the pros and cons of every diet. The study considers the diets in detail with reasoning for inclusion of different hydrocarbons, fats and proteins, with a special emphasis on the sport-specific hydrocarbon additives. Practical applications of the above methods shall take into consideration the glycogen-driven muscular energy supply mechanism. The authors give and analyze the evidence showing that the hydrocarbon barrier overcoming technologies are much more important for the medium-class athletes than for the elite ones.