Creatine is not an essential nutrient, as it is manufactured in the human body from L-arginine, glycine, and L-methionine. In humans and animals, approximately half of stored creatine originates from food (mainly from meat).
The enzyme GATM is a mitochondrial enzyme responsible for catalyzing the first rate-limiting step of creatine biosynthesis, and is primarily expressed in the kidneys and pancreas. The second enzyme in the pathway GAMT is primarily expressed in the liver and pancreas.
Extensive research over the last decade has shown that oral creatine supplementation at a rate of 5 to 20 grams per day appears to be very safe and largely devoid of adverse side-effects while at the same time, effectively improving the physiological response to resistance exercise, increasing the maximal force production of muscles in both men and women.
Creatine And Athletic Performance
Creatine is often taken by athletes to help as a supplement for those wishing to gain muscle mass (bodybuilding). There are a number of forms but the most common are creatine monohydrate (creatine complexed with a molecule of water). A number of methods for ingestion exist: as a powder mixed into a drink, or as a capsule or caplet. Once ingested, creatine is highly bioavailable, whether it is ingested as the crystalline monohydrate form, the free form in solution, or in meat. Creatine salts easily become the free form when dissolved in aqueous solution.
There is scientific evidence that short term creatine use can increase maximum power and performance in high-intensity anaerobic repetitive work (periods of work and rest) by 5 to 15%. This is mainly bouts of running/cycling sprints and multiple sets of weightlifting. Single effort work shows an increase of 1 to 5%. This refers mainly to single sprints and single lifting of 1-2RM weights. However, some high profile studies show no ergogenic effect at all.
Studies in endurance athletes have been less than promising, most likely because these activities are sustained at a given intensity and thus do not allow for significant intra-exercise synthesis of additional creatine phosphate molecules. Ingesting creatine can increase the level of phosphocreatine in the muscles up to 20%.
Since body mass gains of as much as 1 kg can occur in a week's time, many studies suggest that the gain is simply due to greater water retention inside the muscle cells. Other studies, however, have shown that creatine increases the activity of satellite cells, which make muscle hypertrophy possible. Creatine supplementation appears to increase the number of myonuclei that satellite cells will 'donate' to damaged muscle fibers, which increases the potential for growth of those fibers. This increase in myonuclei probably stems from creatine's ability to increase levels of the myogenic transcription factor MRF4.
The preponderance of evidence suggests that creatine use for egrogenisic purposes in anaerobic athletics is both valid and safe. Statistical data suggests that a dosing of 100mg/kg of bodyweight divided evenly over 3 meals is the safe effective threshold dose for maximum sports performance.
*Note the author could find no meaningful studies elucidating dosage duration data. Author recommends discontinuing creatine usage after 8 weeks and suggests a 4 week interval of non use.