What is Creatine?
When we told our friends that we were writing a book on creatine, some of them had quizzical responses. "You're writing on creating? Creating what?" "Is it an herb?"

Creatine is a nutrient that is naturally found in our bodies. It is made from a combination of the three amino acids arginine, glycine and methionine. Creatine helps provide the energy our muscles need to move, particularly movements which are quick and explosive in nature. This includes the types of motion involved in most sports. Approximately 95 percent of the body's creatine supply is found in the skeletal muscles. The remaining five percent is scattered throughout the rest of the body, with the highest concentrations in the heart, brain and testes. (Sperm is chock-full of creatine!)

The human body gets most of the creatine it needs from food or dietary supplements. Creatine is easily absorbed from the intestinal tract into the bloodstream. When dietary consumption is inadequate to meet the body's needs, a limited supply can be synthesized from the amino acids arginine, glycine and methionine. This creatine production occurs in the liver, pancreas and kidneys.

How Does Creatine Work?
Creatine is an essential player in one of the three primary energy systems used for muscle contraction. It exists in two different forms within the muscle fiber: as free (chemically-unbound) creatine and as creatine phosphate. This latter form of creatine makes up two-thirds of the total creatine supply. When your muscles contract, the initial fuel for this movement is a compound called ATP (adenosine triphosphate). ATP provides its energy by releasing one of its phosphate molecules. It then becomes a different compound called ADP (adenosine diphosphate). Unfortunately, there is only enough ATP to provide energy for about ten seconds, so for this energy system to continue, more ATP must be produced. Creatine phosphate comes to the rescue by giving up its phosphate molecule to ADP, recreating ATP. This ATP can then be "burned" again as fuel for more muscle contraction. (We'll discuss all this in greater detail in Chapter Six.)

The bottom line is that your ability to regenerate ATP depends on your supply of creatine. The more creatine you have in your muscles, the more ATP you can remake. This allows you to train your muscles to their maximum potential. It's that simple. This greater ATP resynthesis also keeps your body from relying on another energy system called glycolysis, which has lactic acid as a byproduct. This lactic acid creates the burning sensation you feel during intense exercise. If the amount of acid becomes too great, muscle movement stops. But if you keep on regenerating ATP because of all the creatine you have, you can minimize the amount of lactic acid produced and actually exercise longer and harder. This helps you gain strength, power and muscle size; and you won't get fatigued as easily.

Creatine has also been shown to enhance your body's ability to make proteins within the muscle fibers. Two of these proteins, actin and myosin, are essential to all muscle contraction. So when you build up your supply of these contractile proteins, you actually increase your muscle's ability to perform physical work. And the more work you do (whether it's lifting weights or running 100-meter dashes), the stronger you become over time.