What is stored in muscle cells as glycogen?

Glycogen is a form of stored glucose that is primarily found in muscle and liver cells. When the body has an excess amount of glucose, particularly after consuming carbohydrates, it converts this glucose into glycogen through a process called glycogenesis. The stored glycogen can then be broken back down into glucose when the body requires energy, especially during physical activities or periods of fasting. This process, known as glycogenolysis, allows for a quick source of energy when needed.

In essence, muscle cells store glycogen as a readily available energy reserve that can support muscle contraction and general bodily functions during times of increased energy demand, such as exercise.