Well, the skeleton muscle cells are responsible primary for actually using the glycogen to break it down to glucose and use that glucose in glycolysis to actually form ATP molecules so that we can carry out different types of voluntary motion, for instance, moving my hand back and forth. So our body also depends on glycogen breakdown during periods of rapid activity, for example, sprinting. And the glucose obtained from glycogen can be used to produce energy under anaerobic conditions. And this is a very important distinction because other sources of energy, for instance fatty acids, depend on oxygen. But in the case of glycogen, we can actually break down glycogen into glucose and produce energy without using oxygen. So glycogen can be stored in two types of cells.