The phosphorylation status of creatine, reflecting the cell's energy state, changes dynamically with cellular energy demand, such as during exercise.

“what determines the phosphorylation status of creatine about 120 grams how much of it has an inorganic that just completely unrelated from the synthesis that's a matter of the energy state of the cell so just like ATP gets used when you use energy creatine phosphate in when you're in so instead of do we have an enzyme so the way that you know for example like AMPK is a great surrogate for ATP adp a MP right it really gives you a sense of the energetics do we have similar enzymes that give us a sense of C P versus C creatine phosphate versus creatine I don't think there's an analogous enzyme but there's a completely analogous energy state so when you're exercising for example your ATP levels go down your aim peak levels go up your creatine phosphate levels go down your creatine levels go up when you recover everything reverses”