<Tr> <Td> </Td> <Td> This article needs more medical references for verification or relies too heavily on primary sources . Please review the contents of the article and add the appropriate references if you can . Unsourced or poorly sourced material may be challenged and removed . (June 2015) </Td> <Td> </Td> </Tr> <P> Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in humans, animals, fungi, and bacteria . The polysaccharide structure represents the main storage form of glucose in the body . </P> <P> Glycogen functions as one of two forms of long - term energy reserves, with the other form being triglyceride stores in adipose tissue (i.e., body fat). In humans, glycogen is made and stored primarily in the cells of the liver and skeletal muscle . In the liver, glycogen can make up from 5--6% of the organ's fresh weight and the liver of an adult weighing 70 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) and the skeletal muscle of an adult weighing 70 kg can store roughly 400 grams of glycogen . The amount of glycogen stored in the body--particularly within the muscles and liver--mostly depends on physical training, basal metabolic rate, and eating habits . Small amounts of glycogen are also found in other tissues and cells, including the kidneys, red blood cells, white blood cells, and glial cells in the brain . The uterus also stores glycogen during pregnancy to nourish the embryo . </P> <P> Approximately 4 grams of glucose are present in the blood of humans at all times; in fasted individuals, blood glucose is maintained constant at this level at the expense of glycogen stores in the liver and skeletal muscle . Glycogen stores in skeletal muscle serve as a form of energy storage for the muscle itself; however, the breakdown of muscle glycogen impedes muscle glucose uptake, thereby increasing the amount of blood glucose available for use in other tissues . Liver glycogen stores serve as a store of glucose for use throughout the body, particularly the central nervous system . The human brain consumes approximately 60% of blood glucose in fasted, sedentary individuals . </P>

Which two forms of energy do muscles produce