What Happens When Glycogen Is Stored in the Liver and Muscles?

November 27, 2025 •

3 min read

While the total mass of glycogen stored in the muscles is greater than in the liver, these two organs perform very different functions with this energy reserve. Glycogen is the stored form of glucose, created when the body has excess glucose from the carbohydrates you eat. This critical process, known as glycogenesis, serves as a short-term energy reservoir for both the body as a whole and the muscles specifically.

Quick Summary

The body stores excess glucose as glycogen in the liver and muscles. Liver glycogen maintains steady blood sugar for the whole body, while muscle glycogen provides fuel for the muscles during exercise. The breakdown process is tightly regulated by hormones like insulin and glucagon.

Key Points

Divergent Functions: Liver glycogen primarily regulates blood sugar for the entire body, while muscle glycogen serves as an immediate, localized energy source for muscle cells.
Enzyme Difference: The liver can release glucose into the bloodstream because it contains the enzyme glucose-6-phosphatase, which is absent in muscle cells.
Hormonal Control: Insulin promotes glycogen synthesis (glycogenesis) after eating, while glucagon (liver) and epinephrine (muscles) trigger glycogen breakdown (glycogenolysis) when energy is needed.
Storage Capacity: Muscles store approximately three-quarters of the body's total glycogen, although the liver has a higher concentration relative to its mass.
Metabolic Disorders: Genetic defects in glycogen metabolism can lead to glycogen storage diseases (GSDs), causing hypoglycemia or exercise intolerance depending on the affected enzyme.
Athletic Performance: Optimizing glycogen stores through carbohydrate intake is crucial for athletes to fuel intense and prolonged physical activity and ensure proper recovery.

The Core Process of Glycogen Storage

Glycogen is a multibranched polysaccharide of glucose that acts as a short-term energy reserve in animals. After a carbohydrate-rich meal, insulin is released, promoting glucose uptake by cells and its conversion to glucose-6-phosphate, initiating glycogenesis. Glucose-1-phosphate is then added to existing glycogen chains. The branched structure allows for rapid breakdown when needed.

The Divergent Roles of Liver and Muscle Glycogen

Liver and muscles store glycogen, but their functions differ significantly due to a specific enzyme.

Liver Glycogen: The Body's Glucose Bank

The liver stores about 100-120 grams of glycogen, representing 5–6% of its weight, primarily to maintain stable blood glucose for the entire body. When blood glucose drops, glucagon signals the liver to break down glycogen into glucose via glycogenolysis. The liver contains glucose-6-phosphatase, enabling it to release free glucose into the bloodstream. Liver glycogen levels change throughout the day, decreasing during fasting and increasing after meals.

Muscle Glycogen: Fuel for Action

Muscle contains more total glycogen (around 400 grams) but at a lower concentration (1–2% of muscle mass). This serves as a local energy source for the muscle cells. Muscle cells lack glucose-6-phosphatase, so they cannot release glucose into the blood. Glucose-6-phosphate from muscle glycogenolysis enters glycolysis for ATP production during contraction. Muscle glycogen is the main fuel during high-intensity exercise and is stored in distinct locations within muscle fibers.

Comparison Table: Liver vs. Muscle Glycogen


Feature	Liver Glycogen	Muscle Glycogen
Primary Function	Maintains overall blood glucose homeostasis.	Provides immediate energy for muscle contraction.
Glucose Release	Can release glucose into the bloodstream for the entire body.	Glucose is retained for the muscle's own use and is not released into the blood.
Total Storage Amount	Roughly 100-120 grams in an adult.	Approximately 400 grams in an adult.
Storage Concentration	Higher concentration (5–6% of organ weight).	Lower concentration (1–2% of muscle mass).
Regulatory Hormones	Influenced by both glucagon (breakdown) and insulin (synthesis).	Primarily regulated by insulin (synthesis) and epinephrine (breakdown).

The Breakdown of Glycogen: Glycogenolysis

Glycogenolysis breaks down glycogen into glucose subunits when energy is needed. Hormonal signals (glucagon or epinephrine) activate glycogen phosphorylase, which cleaves the α-1,4 bonds, releasing glucose-1-phosphate. A debranching enzyme removes α-1,6 linkages. Glucose-1-phosphate converts to glucose-6-phosphate, which becomes free glucose in the liver or enters glycolysis in muscle.

Health Implications of Glycogen Storage

Glycogen Storage Diseases (GSDs) are inherited disorders affecting glycogen metabolism enzymes. Symptoms vary based on the affected enzyme and tissue. Examples include GSD Type I (liver/kidney glycogen accumulation, low blood sugar) and GSD Type V (muscle glycogen phosphorylase deficiency, exercise intolerance).

Optimizing Glycogen Storage

Athletes optimize glycogen stores by consuming carbohydrates after exercise for muscle glycogen replenishment, often combining carbs and protein. Carbohydrate loading is used before endurance events. A balanced diet with carbohydrates supports daily energy.

Conclusion

Storing glycogen in the liver and muscles is a vital and distinct process. Liver glycogen maintains blood sugar for the whole body, while muscle glycogen fuels muscle activity. These processes are regulated by hormones like insulin and glucagon, ensuring efficient energy management. Understanding these roles is key to comprehending metabolism and nutrition. For more information, consult resources like the National Institutes of Health.

National Institutes of Health

Frequently Asked Questions

Muscle cells lack the enzyme glucose-6-phosphatase, which is necessary to convert stored glucose-6-phosphate back into free glucose. This means the glucose from muscle glycogen is trapped and can only be used by the muscle cell itself for energy.

The primary function of liver glycogen is to maintain stable blood glucose levels. When blood sugar drops, the liver breaks down its glycogen stores and releases glucose into the bloodstream to supply energy to the brain and other organs.

After consuming carbohydrates, your body breaks them down into glucose. Elevated blood glucose triggers the pancreas to release insulin, which signals the liver and muscles to take up the excess glucose and store it as glycogen through a process called glycogenesis.

During a workout, your muscles primarily use their own stored glycogen for fuel. The intensity of the exercise determines how quickly these stores are depleted. The higher the intensity, the faster muscle glycogen is used.

While the liver has a higher concentration of glycogen per weight, the total mass of skeletal muscle in the body is far greater. Therefore, the body stores more total glycogen in the muscles than in the liver.

A glycogen storage disease is a group of rare, inherited metabolic disorders caused by a genetic deficiency in an enzyme involved in glycogen synthesis or breakdown. This can lead to abnormal glycogen accumulation and related health issues.

Glycogen itself does not convert to fat. However, if glycogen stores are completely full and there is still excess glucose from carbohydrate intake, the body can convert this surplus glucose into triglycerides for long-term storage in fat cells.