Glycogen is stored in skeletal muscles and the liver and is of great importance as a primary source of energy for muscle contractions, especially during high intensity exercise.
It is considered the main storage form of glucose and is found mainly in the liver and muscles, with the kidneys and intestines adding minor storage sites.
It is a complex carbohydrate (polysaccharide) made of glucose units that are released when it is digested, broken down or metabolized, and makes an energy reserve that can be quickly mobilized to meet a sudden demand for glucose, but one that is less compact than the energy reserves of triglycerides .
Glycogen is a very large branched glucose homopolymer containing about 90% alpha-1,4-glucosidic linkages and 10% alpha-1,6 linkages.
The glycogen stored within the muscles can only be used locally by the muscle that it is stored in.
Muscle glycogen lacks the enzyme needed to allow it to pass into the blood stream and it is this lack of enzyme that means muscle glycogen can only be used by the muscle it is stored in.
Now the glycogen stored in the liver is different that in muscle in that it can pass into the blood stream.
The ability of liver glycogen to go into the blood stream means that the liver can give its glycogen to the rest of the body via the bloodstream.
The muscles can store about 1 - 2 percent in glycogen and the liver can store about 8 - 10 percent.
Even thought the liver can hold a greater percentage of glycogen compared to the muscles, the muscles still hold more in total because there is a lot more muscle mass then liver mass.
Glycogen is a very important energy source for the body, and is again the primary energy source.
So for all those who may be trying to burn fat remember that your body will burn glycogen way before it starts to burn fat stores.
So you should design a training plan that tries to deplete the glycogen stores before you even start your cardio.