What is Creatine?
Creatine is a chemical that is normally found in the body, mostly in muscles but also in the brain. It is commonly found in the diet in red meat and seafood. Creatine can also be made in the laboratory (see our list of best creatine supplements).
Creatine is most commonly used for improving exercise performance and increasing muscle mass in athletes and older adults. There is some science supporting the use of creatine in improving the athletic performance of young, healthy people during brief high-intensity activity such as sprinting. Because of this, creatine is often used as a dietary supplement to improve muscle strength and athletic performance. In the U.S., a majority of sports nutrition supplements (see pre-workout supplements), which total $2.7 billion in annual sales, contain creatine.
Creatine is allowed by the International Olympic Committee, National Collegiate Athletic Association (NCAA), and professional sports. However, the NCAA no longer allows colleges and universities to supply creatine to their students with school funds. Students are permitted to buy creatine on their own and the NCAA has no plans to ban creatine unless medical evidence indicates that it is harmful. With current testing methods, detection of supplemental creatine use would not be possible.
In addition to improving athletic performance, creatine is also taken by mouth for creatine deficiency syndromes that affect the brain, chronic obstructive pulmonary disease (COPD), congestive heart failure (CHF), depression, diabetes, fibromyalgia, Huntington’s disease, disease that cause inflammation in the muscles (idiopathic inflammatory myopathies), Parkinson’s disease, diseases of the muscles and nerves, multiple sclerosis, muscle atrophy, muscle cramps, breathing problems in infants while sleeping, head trauma, Rett syndrome, an eye disease called gyrate atrophy, inherited disorders that affect the senses and movement, schizophrenia, muscle breakdown in the spine, and recovery from surgery. It is also taken by mouth to slow the worsening of amyotrophic lateral sclerosis (ALS, Lou Gehrig’s disease), osteoarthritis, rheumatoid arthritis, McArdle’s disease, and for various muscular dystrophies.
People apply creatine to the skin for aging skin.
Creatine’s Effect on Performance
“The majority of studies focusing on creatine supplementation report an increase in the body’s’ creatine pool”
“There is a positive relationship between muscle creatine uptake and exercise performance”
“Significant increase [observed] in strength performance after 12 weeks creatine supplementation with a concurrent periodized heavy resistance training protocol”
“It is regularly reported that creatine supplementation, when combined with heavy resistance training leads to enhanced physical performance, fat free mass, and muscle morphology”
“Usually, consumers do not report any adverse effects, but body mass increases”
Responders vs. Non-Responders
“Conflicting results can be explained by the possibility that the supplemented groups were formed by a greater amount of non-responders”
“Responders showed the greatest percentage of type II fibers followed by quasi responders and non-responders”
“There was evidence of a descending trend for responders to have the highest percentage of type II fibers”
Check out our list of best creatine supplements
Full Excerpt on Non-Response vs. Response
Syrotuik and Bell  investigated the physical characteristics of responder and non-responder subjects to creatine supplementation in recreationally resistance trained men with no history of CM usage. The supplement group was asked to ingest a loading dosage of 0.3 g/kg/d for 5 days. The physiological characteristics of responders were classified using Greenhaff et al  criterion of >20 mmol/kg dry weight increase in total intramuscular creatine and phosphocreatine and non responders as <10 mmol/kg dry weight increase, a third group labeled quasi responders were also used to classify participants who fell in between the previously mentioned groups (10-20 mmol/kg dry weight). Overall, the supplemented group showed a mean increase in total resting muscle creatine and phosphocreatine of 14.5% (from 111.12 ± 8.87 mmol/kg dry weight to 127.30 ± 9.69 mmol/kg dry weight) whilst the placebo group remained relatively unaffected (from 115.70 ± 14.99 mmol/kg dry weight to 111.74 ± 12.95 mmol/kg dry weight). However when looking at individual cases from the creatine group the results showed a variance in response. From the 11 males in the supplemented group, 3 participants were responders (mean increase of 29.5 mmol/kg dry weight or 27%), 5 quasi responders (mean increase of 14.9 mmol/kg dry weight or 13.6%) and 3 non-responders (mean increase of 5.1 mmol/kg dry weight or 4.8%). Using muscle biopsies of the vastus lateralis, a descending trend for groups and mean percentage fiber type was observed. Responders showed the greatest percentage of type II fibers followed by quasi responders and non-responders. The responder and quasi responder groups had an initial larger cross sectional area for type I, type IIa and type IIx fibers. The responder group also had the greatest mean increase in the cross sectional area of all the muscle fiber types measured (type I, type IIa and type IIx increased 320, 971 and 840 μm2 respectively) and non-responders the least (type I, type IIa and type IIx increased 60, 46 and 78 μm2 respectively). There was evidence of a descending trend for responders to have the highest percentage of type II fibers; furthermore, responders and quasi responders possessed the largest initial cross sectional area of type I, IIa and IIx fibers. Responders were seen to have the lowest initial levels of creatine and phosphocreatine. This has also been observed in a previous study  which found that subjects whose creatine levels were around 150 mmol/Kg dry mass did not have any increments in their creatine saturation due to creatine supplementation, neither did they experience any increases of creatine uptake, phosphocreatine resynthesis and performance. This would indicate a limit maximum size of the creatine pool.
In summary responders are those individuals with a lower initial level of total muscle creatine content, greater population of type II fibers and possess higher potential to improve performance in response to creatine supplementation.
Buffered Creatine (Kre-Alkalyn)
“Neither manufacturers recommended doses of KA (1.5 g/d) or KA with equivalent loading (20 g/d for 7-days) and maintenance doses (5 g/d for 21-days) of CrM promoted greater changes in muscle creatine content”
“There was no evidence that supplementing the diet with a buffered form of creatine resulted in fewer side effects than CrM”
Creatine Side Effects
“Gastrointestinal disturbances and muscle cramps have been reported occasionally in healthy individuals, but the effects are anecdotal”
“Liver and kidney dysfunction have also been suggested on the basis of small changes in markers of organ function and of occasional case reports, but well controlled studies on the adverse effects of exogenous creatine supplementation are almost nonexistent”
“We did not find any adverse effects on renal function”
“Creatine (/ˈkriːətiːn/ or /ˈkriːətɪn/) is a nitrogenous organic acid that occurs naturally in vertebrates and helps to supply energy to all cells in the body, primarily muscle. This is achieved by increasing the formation of adenosine triphosphate (ATP). Early analysis showed that human blood is approximately 1% creatine, and the highest concentrations are found in animal blood, brain (0.14%), muscle (0.50%), and testes (0.18%). The liver and kidney contain approximately 0.01% creatine.
Creatine was identified in 1832 when Michel Eugène Chevreul isolated it from the basified water-extract of skeletal muscle. He later named the crystallized precipitate after the Greek word for meat, κρέας (kreas).
Apart from its pharmacological effects, creatine content (as a percentage of crude protein) can be used as an indicator of meat quality.
In solution, creatine is in equilibrium with creatinine. Creatine is a derivative of the guanidinium cation.”