Muscles allow you to exercise and move heavy objects and are necessary for basic activities like breathing, pumping blood, and pretty much anything else you do. On a molecular level, muscles work based on the binding, movement, and rebinding of molecules called actin and myosin. This process involves the hydrolysis of ATP to generate energy.

For your muscles to move, myosin first attaches to actin, forming a bridge. At this point, ADP and a phosphate group are attached to the myosin. The myosin bends (this is what actually controls movement), releasing the ADP and phosphate. Then a new ATP molecule binds again, and then the myosin releases the actin. The ATP is then hydrolyzed, putting the myosin back into its original position, at which point the cycle can begin again.