What is Glycogen?
When we eat carbohydrates, our body changes it into a form of sugar called ‘glucose’ that can be used for energy. The glucose, in turn, is changed to Glycogen, a form of sugar that can be easily stored by our muscles and liver. It is the predominant storage form of glucose and carbohydrates in animals and humans.
While glycogen is indispensable to athletes, we have a very limited capacity to store it. For example, carbohydrates account for only about 1-2% of total bodily energy stores1. Most of this is stored as glycogen in muscle (80%) and liver (14%), and about 6% is stored in the blood as glucose. Despite its limited storage capacity, glycogen is crucial for energy production at all levels of effort. At rest, muscle glycogen is used for about 15-20% of energy production. At moderate intensities (~55-60% of max) glycogen usage could rise to as much as 80-85%2, and this increases even more at higher exercise intensities.
Research has shown that aerobic endurance is directly related to the initial muscle glycogen stores, that strenuous exercise cannot be maintained once these stores are depleted, and that perception of fatigue during prolonged intense exercise parallels the decline in muscle glycogen3.
The important take home message
Ensure you are optimizing glycogen stores before exercise, maintaining it during exercise, and replenishing it after exercise. The impact of carefully designed nutritional strategies can be monitored via MuscleSound.
- Goodman, MN. Amino acid and protein metabolism. In Exercise, nutrition and energy metabolism, Eds. E.S. Horton, R.L. Tertujn, 89-99. New York: Macmillan.
- Katz A, Broberg S, Sahlin K, Wahren J. Leg glucose uptake during maximal dynamic exercise in humans. Am J Physiol. 251(1 Pt 1):E65-70. 1986
- Ivy, JL. Regulation Of Muscle Glycogen Repletion, Muscle Protein Synthesis And Repair Following Exercise Journal of Sports Science and Medicine (2004) 3, 131-138.