And that's what we mean by an interconvertible form. We can go from phosphorase B to phosphorylase A bidactivity of phosphorase kinase, but this requires ATP molecules. Now let's discuss when phosphorase B predominates and when phosphorase A actually predominates in our body. So let's discuss low energy charge conditions. Remember that energy charge, loosely speaking is simply the ratio of ATP to A and P inside our cells. And so if we have low energy charge values within our skeleton muscle cells, we have a low ATP concentration relative to A and P. And what that means is our cells want to produce more ATP molecules and so they want to break down glycogen to glucose to use the glucose via glycolysis to form ATP.