I’m not sure why, but I feel a responsibility to address this.
ATP is the primary source of energy for all metabolism that occurs within the body. It is the energy currency, if you will. There are three primary energy systems that contribute to the production of ATP:
This discussion involves only the phoshopcreatine (PCr) system.
An ATP molecule is an adenosine bonded to three phosphates. ATPase catalyzes the reaction that breaks down ATP into ADP, an inorganic phosphate and energy, which is used to perform all energy-requiring processes.
ATP ===(ATPase)===> ADP + Pi + energy
One way that ATP stores can be restored is via the PCr system. Creatine Kinase (CK) catalyzes the reaction that creates ATP (and creatine) from PCr and ADP:
PCr + ADP ===(CK)===> Cr + ATP
The PCr system predominates during short, high-intensity activities (i.e. sprinting, the early portion of a weight-lifting set, etc.) and at the beginning of any activity.