Creatine Supplementation

Creatine is marketed as "nature's muscle builder" and "the most legitimate sports supplement around." . Supplement labels state that "creatine is converted to phosphocreatine, which is important for short energy bursts such as sprinting and weight lifting" and that "depletion of phosphocreatine can result in muscle fatigue and fading muscle power." Claims are also made that supplementation increases muscle body mass.

One teaspoon of powder contains 5 grams (g) of creatine monohydrate. The recommended daily dose is 1-2 teaspoons dissolved in 8 ounces of water or sweetened beverage. Manufacturers and distributors suggest a five- to seven-day loading phase with intake of 10-20 g (2-4 scoops) daily to fill up the muscle. The maintenance phase of 5-10 g/day is recommended before and/or immediately following a workout. This protocol is claimed to increase creatine muscle stores by 20-50%.

Role In Muscle Contraction

To meet the demands of a high-intensity exercise, such as a sprint, muscles derive their energy from a series of reactions involving adenosine triphosphate (ATP), phosphocreatine (PCr), adenosine diphosphate (ADP), and creatine. ATP, the amount of which is relatively constant, provides energy when it releases a phosphate molecule and becomes ADP. Creatine supplements increase the storage of PCr, thus making more ATP available to fuel the working muscles and enable them to work harder before becoming fatigued.

Sources

The body's pool of creatine can be replenished either from food (or supplements) or through synthesis from precursor amino acids. Dietary sources include beef, tuna, cod, salmon, herring, and pork . The normal dietary intake of creatine is 1-2 g/day, although vegetarians may consume less . Dietary creatine is absorbed from the intestines into the bloodstream. If the dietary supply is limited, creatine can be synthesized from the body stores of the amino acids glycine, arginine, and methionine.

The maximum amount of creatine the body can store is about 0.3 gram per kilogram of body weight . Athletes with high creatine stores don't appear to benefit from supplementation, whereas individuals with the lowest levels, such as vegetarians, have the most pronounced increases following supplementation. Without supplementation, the body can replenish muscle creatine at the rate of about 2 g/day .

Although creatine is a natural component of food, the amount of food required to supersaturate the muscle with PCr may not be feasible. It may be beneficial to avoid caffeine if taking creatine supplements. One study showed that caffeine diminished strength gains seen with creatine use.


Adverse Effects

Creatine supplementation often causes weight gain that can be mistaken for increase in muscle mass. Increasing intracellular creatine may cause an osmotic influx of water into the cell because creatine is an osmotically active substance . It is possible that the weight gained is water retention and not increased muscle. The retention of water may be connected to reports of muscle cramps, dehydration, and heat intolerance when taking creatine supplements.

Creatine is classified as a "dietary supplement" under the 1994 Dietary Supplement Health and Education Act and is available without a prescription. Creatine is not subjected to FDA testing, and the purity and hygienic condition of commercial creatine products may be questionable.