What process directly supplies your body with energy it needs to change ADP back to ATP?

Answer 1

phosphorylation.

Answer 2

ATP is often considered the energy currency of the cell. It is produced by several mechanisms. In most human cells, the majority of ATP is produced by a process called oxidative phosphorylation, which takes place in the mitochondria. Energy from the breakdown of nutrients is carried by intermediates to the electron transport chain in the inner mitochondrial membrane. This chain produces a proton concentration gradient from the energy provided by the intermediates, with many more protons concentrated in the intermembrane space than in the matrix (innermost compartment) of the mitochondria. This gradient is like pumping water up to the top of a hill. When you let the water flow downhill, it can do work like spinning a watermill. Protons in the intermembrane space flow through a protein in the inner mitochondrial membrane called ATP synthase, which harness the proton gradient to convert ADP to ATP, a higher energy molecule.

ATP is also produced from substrate-level phosphorylation, a process that occurs during glycolysis. This process produces much less ATP per molecule of glucose than the oxidative phosphorylation, but it does not require mitochondria or oxygen. While most cells with access to glucose use this process, some cells like red blood cells can only use glycolysis and substrate-level phosphorylation for ATP production. During substrate-level phosphorylation, the conversion of ADP to ATP is coupled to the oxidation of a glycolysis intermediate.

There are other mechanisms of ATP regeneration as well, such as coupling the reaction to the conversion of phosphocreatine to creatine (as happens in skeletal muscle cells).