As Layne Norton, Ph.D., explains in the article "Creatine: What It Is and How It Works," "Creatine itself is a fuel source." 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 make the connection that causes rapid muscle contractions, ATP does so by "borrowing" a phosphate molecule from phosphocreatine and combining it with another compound, ADP. Only after a muscle has largely used up its phosphocreative storage does it begin to produce ATP from other sources such as glucose or fats.
"The supplementation with creatine serves to increase the creatine reserves and the availability of phosphocreatine in the body and leads to a faster ATP," writes the exercise physiologist Ciaran Fairman in the article "6 Side Effects of Creatine Unmasked". "Conclusion: The more phosphocreatine you have, the more work you can do before fatigue sets it."
A secondary function of creatine is to draw water into the muscle cells to make them hydrated.
"When Muscle Cells There are some things that are hydrated, with the most notable being increased protein synthesis," explains Norton.
As many lifters will testify, the movement of water into the cell can also make their muscles bigger or fuller. [1