Theory:
Most of the creatine in the diet comes from meat (an 8-ounce steak might have a gram), but about half of the body’s supply is manufactured in the liver and kidneys. On average, your muscles require about 2 grams of creatine a day (somewhat more for muscular people, a bit less for skinny folks), but more or less depending on your activity level and degree of muscle mass
Creatine is stored in muscle cells as phosphocreatine and is used to help generate cellular energy for muscle contractions. It also may increase the amount of water that each muscle cell holds - thus increasing the size of the muscle (and possibly its function as well). Creatine is used in the body to produce creatine phosphate or CP, which can be thought of as a storage form of quick energy. The function of CP is to regenerate the primary supply of cellular energy - which comes from adenosine triphosphate (ATP). ATP supplies energy for all cells in your body. Upon giving up some of its energy, ATP becomes ADP (diphosphate) and needs to be regenerated back to ATP to do it all over again. CP performs this crucial ATP regeneration step by donating a phosphate group to ADP.
Under conditions where rapid resynthesis of ATP is important - such as during repeated bouts of high intensity exercise - a higher muscle concentration of CP may serve as a reservoir of stored energy and, therefore, enhance performance. Although it has not been studied extensively, there may also be a role for creatine in maintaining muscle mass and preventing the muscle wasting that occurs as a result of old age and in chronic conditions such as AIDS and heart failure.
Scientific Support:
Creatine is one of the new breed of dietary supplements - those based on sound scientific theory and backed up by well-controlled studies. At this writing, at least 20 published articles exist to support the efficacy of creatine supplements in improving performance in high intensity, repeated bout activities. Creatine supplements do not appear to enhance physical performance, however, among subjects performing lower intensity endurance activity such as cycling or running.
A number of studies on creatine and athletic performance have clearly shown that its benefits are limited to anaerobic sports such as like weight lifting, sprinting and jumping. No direct performance benefit of creatine has been shown for endurance athletes. Although increased muscle mass could conceivably enhance endurance performance, the weight gain from water and muscle weight may even result in a decline in performance.
The benefits of creatine are likely to be due to an increased ability to train harder - thus increasing strength. This might be good news to athletes who are training intensely, but it means that creatine alone would probably have very little effect on the muscle mass of sedentary individuals.
A significant gain in physical performance in high-intensity exercise has been shown with creatine doses of 20 to 30 g/day, but more recent research is indicating that similar performance benefits are possible with much lower doses in the range of 2-5 grams/day (though benefits may take longer to be noticed).
Taking very large doses of creatine daily seemed to increase the strength of muscular dystrophy patients' muscles by about 10 percent. Although that may be considered a relatively small gain it may be very important to that person who can now pick up a glass of water. Ten grams of creatine per day for 5 days followed by 5 grams per day for another week have produced increases in muscle strength in the legs, hands and feet of patients with muscular dystrophy. Such patients usually have lower creatine levels than healthy people, so boosting muscle stores may help augment cellular energy production and support muscular contraction.
Safety:
Because of its effects on muscle strength and size, creatine is often confused with anabolic steroids. Steroids, which mimic the effects of the male sex hormone testosterone, can result in a wide variety of adverse side effects such as acne, hair loss, testicular shrinkage and psychological problems. Although the long-term effects of prolonged creatine use has not been examined, no obvious adverse effects have been linked to use of creatine as a dietary supplement. Side effects reported anecdotally include gastrointestinal distress, nausea, dehydration and muscle cramping - but none of these effects have been documented in scientific studies.
Although no serious side effects have been scientifically verified in subjects using relatively brief (less than 4 weeks) creatine regimens, there are anecdotal reports of muscle cramping associated with the creatine supplements. Some athletes have reported muscle cramps, muscle tears and dehydration. A cautionary note is also advised, for people with kidney disorders and for those at risk for dehydration (such as exercise in extreme heat or during cutting weight for wrestling or lightweight crew).
Value:
Consumers spent well over $200 million on creatine supplements last year. Creatine has become one of the hottest sports supplements for one major reason - it works. Creatine appears to be effective in specific situations - those activities which are high-intensity and require short bouts of repeated activity (e.g. weight lifting and football). Athletes in other sports may achieve a significant indirect benefit, as creatine supplements may allow more intense levels of weight training, with strength and power benefits transferring to the sport.
Dosage:
The most common regimen for creatine supplementation follows a two-phase cycle with a 5-10 day loading phase (20-25 g/day) followed by a variable length maintenance phase (2-5 g/day) to maintain muscle saturation. It is unclear, however, whether the loading phase is actually needed to achieve the same end result. Creatine absorption appears to be enhanced when the supplement is taken with a high-carbohydrate drink such as fruit juice.
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