As PhD Lane Norton explains in the article “Creatine: What It Is and How It Works,” “Creatine itself is a source of fuel.” More specifically, the phosphate-bound form of creatine is “the first choice of your body’s energy when performing anaerobic activities, such as lifting weights”.
When your body tries to create a compound that causes fast muscle contractions, ATP, it does this by “borrowing” a phosphate molecule from phosphocreatine and combining it with another compound, ADP. Only after the muscle has largely consumed the supply of phosphocreatine, does it begin to produce ATP from other sources, such as glucose or fats.
“Creatine supplementation is used to increase creatine reserves and the availability of phosphocreatine in the body, which leads to faster ATP formation,” writes physical therapist Ciaran Ferman, Ph.D., in the article “6 side effects of corrupted creatine.” “The bottom line: the more phosphocreatine you have, the more work you can do before fatigue sets it up.”
The secondary function of creatine is to draw water into muscle cells, making them more hydrated.
“When muscle cells are hydrated, several things happen, the most notable of which is an increase in protein synthesis,” explains Norton.
According to many athletes, this action of drawing water into the cage can also make their muscles look bigger or fuller.