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Glycogen is a form of glucose that the body stores in the liver and muscles. The liver has a higher glycogen concentration, but as the liver is much smaller than skeletal muscles, most glycogen is stored in the muscles. The body needs carbohydrates to form glucose and glycogen. When the body doesn't need glucose right away, it stores it as glycogen. When the body needs energy, glycogen gets converted into glucose for quick use by the muscles. Glycogen is, therefore, a vital source of energy during exercise, especially endurance events and high-intensity workouts.
| Characteristics | Values |
|---|---|
| What is it? | A form of glucose that the body stores for energy |
| Where is it stored? | In the liver and skeletal muscles (the muscles attached to bones and tendons) |
| How much is stored? | A normal, healthy 70kg male eating a high-carb diet might have around 600g (2,400 calories) of glycogen in their muscles, and 90g in their liver |
| How is it used? | During exercise, the body uses glycogen as an energy source. Glycogen is also used to power the brain and spinal cord |
| How is it restored? | Glycogen is restored by consuming carbohydrates. Carbohydrate-rich recovery shakes or snacks are recommended within 30-60 minutes of finishing intense exercise |
| How is it depleted? | Glycogen stores are depleted through exercise, especially high-intensity activity. They can also be depleted by not consuming enough carbohydrates |
| What happens when it is depleted? | When glycogen stores are depleted, the body becomes fatigued, sluggish, and may experience mood and sleep disturbances |
| How is it produced? | The body converts glucose to glycogen through a process called glycogenesis. The body breaks down glycogen through glycogenolysis |
| How is it regulated? | The hormones glucagon and insulin regulate blood glucose levels and trigger glycogen to convert to glucose and enter the bloodstream |
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What You'll Learn
Glycogen is a stored form of glucose
Glycogen stored in the muscles is used by the muscles themselves, while glycogen stored in the liver is distributed throughout the body, particularly to the brain and spinal cord. The body uses glycogen as fuel during exercise, and the muscles restore glycogen when enough carbohydrates are consumed. During high-intensity activity, glycogen stores in active muscle cells can be significantly reduced. Glycogen is also supplied to the body through glucose gels and energy chews, which are used by runners to boost their performance during long runs.
The amount of glycogen stored in the body can vary depending on factors such as physical activity levels, energy burned at rest, and diet. For example, a high-carbohydrate diet is key to maximising glycogen stores. Carbohydrate manipulation in the diet can also impact performance, with a low-carb diet potentially stagnating performance improvement.
Glycogen is also important for the regulation of insulin sensitivity. Reduced glycogen content in skeletal muscles increases insulin sensitivity, and the rapid restoration of glycogen content can be important for survival during acute emergencies.
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Glycogen is stored in the liver and muscles
Glycogen is a form of glucose that the body stores in the liver and muscles. It is a fuel source stored in the cytosol of cells, occupying 2% of the volume of cardiac cells, 1%–2% of the volume of skeletal muscle cells, and 5%–6% of the volume of liver cells. The glycogen particles in liver cells can be 10 times larger than those in skeletal muscle cells, with each particle containing over 50,000 glucose molecules.
In humans, glycogen is made and stored primarily in the cells of the liver and skeletal muscle. In the liver, glycogen can make up 5–6% of the organ's fresh weight: the liver of an adult weighing 1.5 kg can store roughly 100–120 grams of glycogen. In skeletal muscle, glycogen is found in a low concentration (1–2% of the muscle mass): the skeletal muscle of an adult weighing 70 kg stores roughly 400–500 grams of glycogen.
Glycogen stored in muscle is primarily used by the muscles themselves, while glycogen stored in the liver is distributed throughout the body, mainly to the brain and spinal cord. The liver glycogen content decreases rapidly during fasting and the liver glycogen content has decreased by 65% after 24 hours of fasting. Muscle glycogen, on the other hand, does not show a major decrease during fasting.
The amount of glycogen stored in the body depends on several factors, including oxidative type 1 fibres, physical training, basal metabolic rate, and eating habits. High-intensity activity, such as repeated sprinting, can quickly lower glycogen stores in active muscle cells. The muscles restore glycogen when sufficient carbohydrates are consumed.
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Muscle glycogen is a vital energy source
During exercise, the body breaks down glycogen through glycogenolysis to fuel muscle cells. The body can quickly deplete glycogen stores during intense and prolonged exercise, especially in active muscle cells. This depletion can lead to feelings of fatigue and sluggishness. Therefore, restoring glycogen through carbohydrate consumption after exercise is essential for recovery and maintaining performance.
The amount of glycogen stored in the body can vary depending on factors such as activity levels, energy expenditure, and diet. A high-carbohydrate diet is crucial for maximising glycogen stores. Carbohydrate-rich meals raise blood glucose levels, prompting the pancreas to produce insulin, which helps cells take up glucose for energy or storage. This process results in the formation of glycogen synthase, an enzyme that links glucose chains.
Glycogen is not only important for athletic performance but also for overall bodily functions. It helps regulate blood glucose levels, and its conversion to glucose provides a quick energy source for muscle cells. Additionally, muscle glycogen may have played a vital role in survival during acute emergencies, providing a rapid energy substrate for "fight or flight" reactions.
In summary, muscle glycogen is indeed a critical energy source, impacting both physical performance and overall physiological functions. Its availability ensures the body has the fuel it needs to sustain activities and maintain homeostasis.
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Glycogen is restored by eating carbohydrates
Glycogen is a form of glucose that the body stores in the liver and muscles. It is a fuel reserve that powers the brain and athletic pursuits, as well as other bodily functions. The body breaks down carbohydrates into glucose, which is then stored as glycogen.
When the body doesn't need glucose right away, it stores it as glycogen. The body can then convert glycogen back into glucose when it needs fuel. This process is called glycogenesis. The body also uses insulin and glucagon to regulate blood glucose levels. Insulin helps the body's cells take up glucose from the bloodstream for energy or storage. When blood glucose levels fall too low, the pancreas releases glucagon, which triggers glycogen in the liver to convert back into glucose and enter the bloodstream.
Glycogen stores can be depleted through exercise, illness, or certain dietary habits. After a workout, it is important to restore glycogen by eating foods that contain carbohydrates. The body can restore glycogen the fastest during the two-hour window right after exercise. It is recommended to eat around 50 grams of carbohydrates every two hours to continue replenishing glycogen levels. If you eat at this rate, it should take about 20 hours to restore all the glycogen you lost.
It is challenging to restore glycogen on a low-carb diet. The body needs an external source of glucose to create glycogen. Without enough carbohydrates, the body won't have enough glycogen, and it will shift into ketosis, using fatty acids as fuel instead. However, some people on low-carb diets ensure they consume enough fat and protein to make up for the lack of carbohydrates.
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Glycogen is important for athletic performance
Glycogen is a form of glucose that the body stores in the liver and muscles. It is the body's predominant source of energy during moderate- to high-intensity exertion. The body breaks down glycogen through a process called glycogenolysis, which it can then use for fuel.
Glycogen is especially important for athletic performance as it is the body's primary source of fuel during exercise. During exercise, the body breaks down glycogen to supply itself with glucose. When muscle glycogen content is high, athletes can spend more time performing at higher intensity levels. For example, soccer players with high muscle glycogen content can spend more time running at moderate to high speeds, and hockey players can skate longer and faster during each shift.
Athletes with low muscle glycogen content will experience a decrease in exertion capacity, as well as an increased risk of overtraining and muscle damage. During moderate- to high-intensity exertion, when glycogen content levels are low, an athlete may enter a catabolic situation (muscle breakdown) where the muscle may “eat itself to feed itself” by increasing the amount of protein and amino acids used for energy. Studies have shown that low carbohydrate diets that cause glycogen depletion are associated with fatigue and a decrease in performance.
Athletes should be educated and encouraged to consume enough carbohydrates to replenish their muscle glycogen stores so that training intensity can be maintained from day to day. Carbohydrate intake should be based on the rates of glycogen depletion and the physical activity being performed.
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Frequently asked questions
Muscle glycogen is the stored form of glucose in the body. It is a fuel source that is stored in the muscles and liver.
The amount of glycogen stored in the muscles varies from person to person. It depends on factors such as body composition, level of activity, and diet. On average, a healthy 70 kg male eating a high-carbohydrate diet might have around 600g of glycogen stored in their muscles.
Glycogen is restored in the muscles by consuming a sufficient amount of carbohydrates. This is especially important after endurance exercises or intense physical activity, as the glycogen stores in the muscles can become substantially reduced.
