As we approach the climax of the summer months, a period marked by increased activity, sport and competition, it is important to consider the vital role nutrition plays towards these endeavors. Since scientists first began to explore the relationship between nutrition and performance, we have come to understand that the food choices we make can uniquely improve our potential to perform. The manipulation of glycogen for exercise performance is a great example of the transformative role nutrition plays within the various components of sport performance. The history and current practice of glycogen loading reflects the pervasiveness of this sound nutritional strategy despite a continued rise in scientific developments concerning nutrition strategies aimed at improving exercise and sport performance.
In 1967, researcher Björn Ahlborg delivered a report on the effects of muscle glycogen during prolonged exercise at an annual meeting of the Swedish Medical Society (Ahlborg, Bergstrom, Edelund & Hultman, 1967). In this investigation, Björn and colleagues identified a relationship between diet and muscle glycogen stores and demonstrated that the capacity for prolonged work is directly correlated to the glycogen store in the working muscles (Ahlborg, Bergstrom, Edelund & Hultman, 1967). Their investigation proved to be notable as it demonstrated the ability to manipulate nutrition for the benefit of exercise performance. In particular, results from their study showed that when a low carbohydrate diet is followed by a high carbohydrate diet, glycogen concentrations first decrease in response to the low consumption of carbohydrates and then rebound to double baseline glycogen concentrations. This phenomenon is known as glycogen supercompensation (Jeukendrup & Gleeson,2010).
This particular carbohydrate loading procedure developed by Björn and colleagues in the1960s is still used by athletes today through various methods to help ensure optimal intake of energy substrates, augment muscle glycogen stores, and to ultimately improve potential for high performance in exercise and sport (Zydek, Michalczyk, Zajac,& Latosik, 2014). Through the investigation of the purpose, methods and current use of glycogen loading techniques we will learn that increasing our understanding regarding the demands of sport and exercise as well as the specific physiologic responses established through strategic manipulation of nutrition is critical for improving exercise performance at a high level. Additionally, this growth in perspective regarding glycogen loading may help us to appreciate the value it can play within a multifaceted and periodized approach to athletes year-round for the purpose of greater exercise and sports performance.
In order to understand the value of glycogen loading to exercise and performance we must first understand the importance of carbohydrates to exercise and performance. The carbohydrate macronutrient is one of the most important sources of fuel for the body during physical activity and at rest. This highly versatile macronutrient is one of the first options for energy needs during various types of activities and intensities and is considered a key fuel for the brain and central nervous system (Williams & Rollo, 2015). Carbohydrates are stored in the form of glycogen in both skeletal muscles and in the liver. On average a person stores about 500 grams of glycogen in their muscles and 100 grams of glycogen in their liver (Jensen, Rustad, Kolnes, & Lai, 2011). Our ability to exercise at a given intensity depends on the capacity of our skeletal muscles to rapidly replace energy (in the form of ATP) used to support all of the energy-demanding processes during exercise. The two metabolic systems that generate energy, or ATP, in skeletal muscle are described as ‘anaerobic’ and ‘aerobic’.
During both anaerobic activity or high intensity activities and aerobic activity or relatively lower intensity activities the production of energy in the form of ATP is fueled in part by the breakdown of glycogen. For instance, during a high intensity activity or an anaerobic activity such as a 6 second sprint, muscle glycogen contributes to about 50% of energy production (Williams & Rollo, 2015). However, as the duration of activity begins to increase and/or the intensity levels begins to decrease, the metabolic system that drives energy production within the body shifts from a mostly anaerobic to aerobic process. Moreover, during aerobic activities or relatively lower intensity and longer duration activities such as long distance running the degradation of glycogen is a slower and less reliant process as compared to its role in anaerobic activities. Despite the diminished role in energy production, glycogen breakdown produces 12 times more ATP during aerobic activities as compared to anaerobic activities (Williams & Rollo, 2015).
The availability of this stored form of carbohydrate has been shown to impact the performance of prolonged sub-maximal, moderate and/or intermittent high-intensity exercise activities greater than 90 minutes. Carbohydrate availability also contributes to an important role in the performance of brief or sustained high-intensity work (Hargreaves, 1996). Through a special process of carbohydrate consumption known as carbohydrate loading, individuals can maximize muscle glycogen stores (as well as beyond normal levels) and thus improve their potential to perform optimally in endurance exercise and events lasting longer than 90 minutes (Beck, Thomson, Swift, & von Hurst, 2015). This process of carbohydrate or glycogen loading can help to delay the onset of fatigue (by approximately 20%) and result in a performance increase of of 2%–3% (Beck, Thomson, Swift, & von Hurst, 2015).
It is important to note that the process of carbohydrate loading is also termed glycogen supercompensation. This term results from findings which show that when carbohydrate loading involves a depletion phase (produced by 3 days of intense training and/or low carbohydrate intake) followed by a loading phase (3 days of reduced training and high carbohydrate intake) glycogen concentrations rebound to super-physiological levels or levels greater than normal. This method is understood as the classical supercompensation protocol. Researchers have also demonstrated that protocols designed to increase muscle glycogen concentrations can be enhanced to a similar level without a glycogen-depletion phase (Sherman, Costill, Fink, & Miller, 1981).
In fact, over the years researchers have continued to produce various protocols which can be used for the process of glycogen loading and/or glycogen supercompensation. Listed below is an example of a glycogen loading protocol used for athletes preparing a week or more in advance for an exercise event or sport competition with a duration greater than 90 minutes.
In addition to the classical supercompensation protocol researchers have demonstrated that glycogen loading can be achieved with a 1 to 2 day modification of the diet and ingestion of carbohydrates at a rate of 10 grams per kilogram of body mass per day as well as a change in training loads (Zydek, Michalzzyk, Zajac & Latosik, 2014). Some researchers have shown that combining physical inactivity with a high intake of carbohydrate enables trained athletes to attain maximal muscle glycogen contents within only 24 hours suggesting that glycogen loading can take place within a 24 hour period (Bussau, Fairchild, Rao, Steele, & Fournier, 2002).
Nonetheless, the practice of glycogen loading has been shown to increase levels of glycogen within muscle and can remain elevated for a number of days. Authors note that athletes following a supercompensation cycle can experience at least 3 days of elevated glycogen levels (Goforth, Arnall, Bennett, & Law, 1997). This elevated response can provide athletes enough time to rest and recover from physical activity and also allow for significantly high levels of glycogen to be maintained in preparation for a specific exercise or sport event. Athletes interested in improving muscle glycogen stores must be aware that the process of carbohydrate loading rests on appropriate consumption of carbohydrates as well as proper amounts of vitamins, minerals and water.
Glycogen loading is a powerful example of how nutrition is increasingly recognized as a key component of optimal exercise and sport performance. As our understanding of the demands of sport and exercise as well as the science and practice of sports nutrition develops we will continue to see notable examples of the far reaching and positive impact nutrition provides to exercise and sport.
In addition, it may be useful to view certain nutrition strategies such as glycogen loading as part of a larger systematic approach to nutrition aimed at improving certain areas related to exercise performance during specific periods. Authors call this strategic aim to obtain adaptations in support of exercise performance through the combined use of nutrition and exercise training (or nutrition only) nutrition periodization (Jeukendrup, 2017).
With the rise of nutrition programs and diets such as the ketogenic diet, “train low, compete high” along with long established nutrition programs such as “glycogen loading” or “supercompensation” it is increasingly important for athletes, coaches, nutritionists and performance specialists to recognize the multifaceted ways in which nutrition planning can help deliver both long term and short term benefit and ultimately result in the production of greater potential and high performance for a given athlete.
Ahlborg, G., Bergstrom, J., Edelund, G., Hultman, E. (1967). Muscle glycogen and muscle electrolytes during prolonged physical exercise. Acta Physiologica Scandinavica, 129-142.
Beck, K. L., Thomson, J. S., Swift, R. J., & von Hurst, P. R. (2015). Role of nutrition in performance enhancement and postexercise recovery. Open Access Journal of Sports Medicine, 6, 259–267.
Bussau, V., Fairchild, T., Rao, A., Steele, P., & Fournier, P. (2002). Carbohydrate loading in human muscle: An improved 1 day protocol. European Journal of Applied Physiology, 87(3), 290-295.
Goforth., H. W., Arnall., D. A., Bennett., B. L., & Law., P. G. (1997). Persistence of supercompensated muscle glycogen in trained subjects after carbohydrate loading. Journal of Applied Physiology, 82(1), 342-347
Jensen, J., Rustad, P. I., Kolnes, A. J., & Lai, Y.-C. (2011). The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin Sensitivity by Exercise. Frontiers in Physiology, (2) 112.
Jeukendrup, A. E. (2017). Periodized Nutrition for Athletes. Sports Medicine (Auckland, N.z.), 47(Suppl 1), 51–63.
Jeukendrup, A. E., & Gleeson, M. (2010). Sport nutrition. Champaign, IL: Human Kinetics.
Sherman, W., Costill, D., Fink, W., & Miller, J. (1981). Effect of Exercise-Diet Manipulation on Muscle Glycogen and Its Subsequent Utilization During Performance. International Journal of Sports Medicine,02(02), 114-118.
Williams, C., & Rollo, I. (2015). Carbohydrate Nutrition and Team Sport Performance. Sports Medicine (Auckland, N.z.), 45(Suppl 1), 13–22.
Zydek, G., Michalzzyk, M., Zajac, A., Latosik, E. (2014) Low- or high-carbohydrate diet for athletes? Trends in Sport Sciences, 2(4), 207-212.