This is important because cells such as brain cells depend almost entirely on glucose for energy. Now, what about skeleton muscle cells? Because not only do liver cells store glucose as glycogen, but our skeleton muscle cells also store the glycogen. 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.