In chemical terms, glycogen is nothing more than a kind of complex carbohydrate – specifically a polysaccharide, i.e., a long-chain polymer of glucose molecules. In biological terms, glycogen forms the principal reserve of carbohydrate storage energy in the body that can be readily mobilized and used as and when a sudden massive need for glucose arises, e.g., during a short-term strenuous activity.
Glycogen is primarily stored in the liver and in the skeletal muscle cells. Though the concentration of glycogen in the muscle cells (1–2%) is much less than that in the liver (8–10%), the total amount of glycogen stored in muscles far exceeds that in the liver because of the much greater mass of muscles in the body.
But how is glycogen energy reserve different from stored energy reserve of triglycerides (stored fats) – another form of stored energy in the body. Well, firstly, glycogen being a carbohydrate is less energy-dense compared to triglycerides – which are fats – but is more readily available for use. Also, glycogen is stored mainly in the liver and the muscles, unlike triglycerides, which are distributed all over the body in the form of subcutaneous body fat.
How does glycogen work as an energy source?
The energy from glycogen is made available by its breakdown (facilitated by the enzyme glycogen phosphorylase) into individual glucose molecules, which is the main energy fuel for the cells. In the liver this process is initiated by glucagon, a hormone produced by the pancreas. Now, the glucagon level is directly related to the blood sugar/glucose level. When your glucose level is low – as a result of which you feel fatigued and devoid of energy – more glucagon is secreted, which in turn instructs the liver to break down glycogen into glucose and pass it into blood in order to restore glucose level back to normal. And when blood glucose level is normal, you start feeling energetic once again. Thus, in addition to providing energy, glycogen also helps regulate blood sugar levels.
In the muscles, however, the breakdown of glycogen is stimulated by muscle contractions, as occurring during workouts. The more intensive the exercise, the more glycogen your muscles will convert into glucose to provide the needed energy, allowing you to continue exercising. However, since the liver can store only a limited amount of glycogen, eventually you will run out of fuel if you don’t replenish your glycogen reserves through proper nutrition.
It may be mentioned that the glycogen stored in the liver can be passed into blood and made accessible to other organs. In contrast, the muscle glycogen can be used only by the muscles, not by other organs, because muscles lack the enzyme that facilitates glucose transport into blood.
The role of glycogen in bodybuilding
Glycogen is the prime fuel for energy in anaerobic bodybuilding exercises like weightlifting and strength training. So, if as a bodybuilder you would like to keep your muscles pumped up all the time with loads of energy during workouts, then you must strive to stockpile your glycogen reserves. Muscle glycogen resynthesis, also known as glycogen supercompensation, by strategically planning the carbohydrate depletion/reloading cycle is the key to building muscle mass and a sculpted body that can fetch laurels in any bodybuilding competition.