WHAT IS CREATINE? Creatine is an energy-rich metabolite found mostly in muscle. It is like a rechargeable battery that powers intense exercise. At rest, it becomes “charged” with phosphate groups to form creatine phosphate. These phosphate groups come in handy when, during intense exercise, ATP (adenosine triphosphate) loses phosphate to become ADP (adenosine diphosphate). Creatine phosphate supplies ADP with the phosphate it needs to be “recharged” to ATP so that exercise may continue.