The Creatine Factor
Creatine monohydrate burst onto the nutrition scene a few years back and its popularity has been quite a phenomenon. It has been called the ultimate ergogenic aid. As a supplement, creatine is believed to exert its influence by increasing muscle creatine and phosphocreatine concentrations, creating a higher rate of ATP resynthesis, resulting in a delay in an onset of muscle fatigue and a facilitated recovery during repeated rounds of high intensity exercise.
Approximately 95% of the body's total creatine/phosphocreatine (also called phosphorylcreatine) pool is found in muscle, with more being located in skeletal muscle than in smooth muscle. Tissues that contain creatine are: skeletal muscle, heart muscle, all smooth muscles, sperm and neural tissue, including the brain. On the average, there are about 120 grams of creatine/phosphocreatine in a typical 70-kilogram male. Of this, 72 to 80.4 grams exist as the phosphocreatine form in resting muscle. Consider the fact that this amount generates enough ATP to contract the muscles in exercise for about four seconds.
Creatine and phosphocreatine undergo irreversible cyclization and dehydration to form creatinine at a rate of approximately two grams of creatinine per day in the typical adult male. This would then represent the amount of creatine that must be gotten from dietary sources or endogenous synthesis to sustain the body supply of creatine and phosphocreatine on a daily basis. The endogenous synthesis of creatine takes place in the liver and kidney, and this creatine is then released into the bloodstream to be actively taken up by the muscle cells. Glycine, arginine and methionine are the three amino acids used in the synthesis of creatine. The body can produce from 1 to 2 grams of creatine per day.
According to Clark's review (Nutrition 14:322-324, 1998), the supplementation of creatine at a rate of 2 to 5 grams per day will increase muscle creatine and phosphocreatine. Dosing at a rate of 20 grams per day for two weeks has lead to marked increases in muscle creatine, which can be maintained with a continued daily dose of five grams. The ingestion of 20 to 30 grams of creatine per day for up to three weeks has been seen to increase muscle creatine about 20%. The general finding has been that 20 grams per day is the loading dose that is used for a period of 6 to 14 days (depending on the study you read) and a maintenance dose of five grams per day is continued throughout the training period. It has been found by Green, et al, that creatine uptake occurs best with a low-fat, high carbohydrate diet. About 70% of the population who have taken creatine demonstrated increases in total muscle creatine. Individuals who have low muscle creatine at the start of a creatine supplementation program get the most striking increases in muscle creatine
A single dose of five grams of creatine raises plasma levels to a peak in one hour, with a return to pre-supplement levels seen in about five hours. This would indicate that the serum half-life of creatine is about two hours. According to the laws of pharmacokinetics, this would give the dose studied of supplemented creatine a serum life span of about 14 hours in the body. Typically, this is determined by multiplying the serum half-life by a factor of seven, provided the administered agent is following first-order kinetics. As mentioned earlier, under normal circumstances the body will turnover about two grams of creatine/phosphocreatine per day. Creatine retention is maximal (about 32%) in the first two days of supplementation. Caffeine may negate the effects of creatine supplementation by inhibiting the resynthesis of phosphocreatine. It has been reported