Creatine (guanidine-acetic acid) is a nitrogenous organic compound found in all types of muscle tissue.(1) 98% of total Cr is contained in skeletal muscle, of which 40% is free Cr and 60% is phosphocreatine. It is also synthesized endogenously by the liver, kidney and pancreas from the precursor amino acids arginine, glycine and methionine.
It is obtained predominantly from the ingestion of meat, fish or liver which contain about 5g/kg. Although endogenous synthesis (replaced at 2g per day ) is adequate to maintain normal levels in individuals on a Cr-free diet, vegetarians are reported to have slightly lower basal levels of Cr compared to individuals who consume meat daily. Cr and PCr are degraded into creatinine, filtered in the kidneys by diffusion and excreted in the urine.(5)
"PC serves a major role in energy metabolism, specifically as a donor of phosphate for energy production. The maintenance of ATP during rapid increases in energy demands is met by breakdown of PCr. The only known enzymatic reaction involving Cr and PCr is the reversible Cr kinase reaction, which is controlled by CKP (creatine kinase)."
PC depletion occurs faster than glycogen depletion and as exercise continues, the high ATP demands are met primarily by anaerobic glycolysis. PCr depletion occurs rapidly at the onset of all-out exercise.
The concentration of PCr appears to correlate with the development of force and my contribute to fatigue. Type II muscle fibers posses higher initial levels and greater rates of utilization of PCr and glycogen the Type I muscle fibers. PCr recovery seems to be slower in Type II fibers. The greater loss and slower recovery of PCr and glycogen following high-intensity exercise in Type II muscle fibers very likely contribute to the reduction in force during high-intensity exercise, as these muscle fibers are predominantly recruited in this type of activity.
Athletes take creatine in the hope of increasing and prolonging energy for anaerobic activities. Evidence that intramuscular stores can be increased by ingesting Cr date back to 1926. The supplement used by athletes is creatine monohydrate which is a synthetic, odorless and tasteless white powder. Creatine ingestion will not increase the muscle creatine content above the body's natural limit which is 5.0g/kg of muscle.(1) "The ergogenic effect of Cr ingestion is most likely a result of increased preexercise availability of Cr and PCr and enhanced PCr resynthesis during recovery from exercise. Therefore, athletes involved in activities that are predominantly anaerobic in nature (high-intensity, short duration) are most likely to benefit from Cr supplementation."
The idea of delaying fatigue and achieving a high force production for a longer period of time has wide athletic applications. There is evidence that supplementation with Cr monohydrate, 20-25g/day for 5-6 days may be of benefit to athletes.
Greenhaff, et al. had 12 physically active but not highly trained subjects perform knee extensions on Cybex isokinetic dynamometer. There was a 1 minute recovery period between each bout of 30 muscle actions. Results revealed the Cr supplemented group was able to significantly reduce the decline in muscle peak torque production. This was attributed to an increased availability of PCr.
Balsom et al. had 16 males perform ten 6 second bouts of high-intensity cycling at 140 revolutions/minute with 30 second rest periods. During the second half of each bout the Cr group was better able to maintain the pedal frequency. This was attributed to an acceleration of PCr resynthesis during the recovery periods, resulting in a higher PCr concentration prior to each single exercise bout.
Ernest et al. supplemented 4 strength trained men with 20g Cr/day for 28 days and showed and increase in 1RM bench press and repetitions performed at 70% of 1RM.
Several other studies corroborate these findings.
Individuals with lower basal levels of muscle Cr tend to gain the largest increases in muscle Cr (as much as 30%) and more likely to increase performance versus someone with already high concentrations of muscle Cr. Muscle Cr may stay elevated for greater than one month. Once the tissue levels have been elevated by prior Cr supplementation (20-25g/day for 5 days), the dosage may be reduced to 3g/day to maintain elevated stores in the muscle.
Increased Cr and PCr levels attenuate ATP degradation during high-intensity muscular activity. This is likely a result of an increased rate of ATP resynthesis from ADP. This increased availability of PCr as an energy source may decrease the usual dependence on anaerobic glycolysis for resynthesis of ATP. Thus, the accumulation of lactate in delayed, allowing the muscle to generate a high force for an extended time.
Increases in performance during intermittent exercise are most likely explained by a greater availability of PCr in the Type II muscle fibers as a result of higher rates of resynthesis during recovery.
The weight gain in subjects was probably due to an increase in total body water; however, an increase in LBM cannot be ruled out.(5)
The only side effect in the literature is an increase in body mass.(5) Anecdotal evidence points to two side effects: muscular cramping due to dehydration and gaseousness.
Study done on running in which 20 athletes completed both of two testing sessions 1 week apart wherein they sprinted three 60m distance trials. For seven days subjects in the treatment group ingested 25g/day of creatine monohydrate. Results indicated that there were no statistically significant effects on velocity between the treatment and non-treatment groups.(4)
Creatine Safety: A Physicians Prospective by Dr. Lynn Myers MD
Dr. Lynn Myers is regarded as one of the countrys foremost experts on creatine. He has been interviewed by CNN Sports, heard on ESPNs "One On One Sports". Dr. Myers has addressed the National Wrestling Coaches Association as a special guest speaker on nutrition. Dr. Myers is a practicing pathologist and Director of Research and Development for NuCare, an Oklahoma company that makes a creatine chewing gum and a chewable creatine wafer. Dr. Myers is available for interviews.
There is now little doubt, when you study the scientific literature and talk to athletes, that creatine improves certain types of athletic performance. This is especially true in power sports such as football, baseball and wrestling that require short-term explosive muscle contraction. Creatine increases muscle mass, strength, explosive power, and stamina. Because of this creatine is our nation's most popular sports supplement.
A recent study found that 48% of Division 1 NCAA male athletes take or have taken creatine. Last year, an estimated that six to eight million pounds were consumed in the United States. Although creatine has been widely used in the U.S. since 1992, and many scientific articles attest to creatines safety, some still caution that creatine has not been used long enough to determine its possible long-term side effects.
Others seem opposed to creatine supplementation purely for philosophic reasons. A typical example of this often-expressed view is a French food safety expert who recently stated that creatine "is contrary to the rules, spirit and significance of sport."
As a pathologist with a lifetime of experience in solving medical puzzles, I have learned the value of reviewing the scientific literature for myself and ignoring rumors and half-truths.
Creatine is a protein made from amino acids. Our body makes one gram each day from protein. We also eat about one gram of creatine each day from meats such as beef, chicken or fish. Creatine is not a source of energy in itself, but stores energy you get from your food. Creatine acts like uncharged battery. When creatine is charged with energy from food, it becomes the major energy source for immediate muscle contraction. When extra creatine is taken to supplement the creatine consumed in meats and produced in our body, still more energy is available for muscle contraction.
Just as medical science learned what vitamins do in the body by studying vitamin deficiencies, we learn about creatine by studying creatine deficiency disorders. Two examples help us to understand creatines role in the body.
First in animal studies, researchers have blocked creatine uptake into the muscle cells from the blood. The result is a loss of fast-twitch (type 11) muscle fibers. This is the type of muscle cell that is first called into action in power sports as football, baseball and wrestling.
Secondly, several naturally occurring creatine deficiencies have been found in children. Because of a genetic defect, these children can not make creatine in their bodies. As a result they have low creatine levels with muscle loss and weakness. Creatine supplementation strengthens these children. Both these examples help us understand that creatine is necessary for healthy, strong muscle.
In times past, hunters such as the American Plains Indians, African Tribes, and Eskimos ate huge amounts of meat. During the winter season, they sometimes consumed an all-meat diet. Since meat contains about one gram of creatine per each half pound, these hunters easily consumed 3-5 grams of creatine per day. Remarkably this creatine dosage is similar to that recommended today by many scientists. Since mankind began and remained a hunter for thousands of years, it seems highly unlikely that heavy consumption of meat containing creatine is dangerous.
While creatine is "new" to many in the U.S., it is not "new" to the rest of the world. The Russians and other Eastern Block countries used creatine as a sport supplement for at least 20 years. Recently I spoke to a Russian Sports scientist who candidly told me that the Russians never found any injurious effects while using creatine.
In the West creatine has been manufactured and sold as a sport supplement for about nine years. Creatine was used by successfully in the West in the 1992 Olympics. As creatine began to be readily available in the United States many bodybuilders began taking creatine in massive amounts. Thinking that if a little is good, more must be better they took twenty, forty and even sixty grams of powder a day, all without injurious effect on their health. If creatine were as dangerous as some would have you believe these human "guinea pigs" would have clearly demonstrated serious side-effects. This has not been the case.
During the past few years medical scientists and physicians have begun experiments to learn if creatine can be used to treat various medical disorders. In these carefully done studies under close medical supervision, doctors have not reported any injurious creatine effects on the body. On the contrary, many of these studies show promise that creatine can be helpful in preventing or slowing certain disorders such as Lou Gehrigs Disease, Huntingtons Disease, and Parkinsons Disease.
The American College of Sports Medicine hosted a roundtable discussion by several top scientists interested in creatine. They reported in their abstract that "there is no definitive evidence that creatine supplementation causes gastrointestinal, renal, and/or muscle cramping complications." 1
Despite all the rumor and speculation that we have all heard over the past few years, I find no credible evidence that creatine supplementation is harmful in anyway to our health. On the contrary, an ample amount of creatine is absolutely necessary for healthy muscle and other cellular function.
Med. Sci. Sports Exerc. 2000 Mar; 32 (3): p. 706-17
Effects of Long-term Creatine Supplementation on Liver and Kidney Functions in American College Football Players.
Mayhew DL, Mayhew JL, Ware JS.
Exercise Science Program at Truman State University, Kirksville, MO 63501 and the Athletic Department at Truman State University, Kirksville, MO.
The purpose of this study was to determine the effect of long-term Cr supplementation on blood parameters reflecting liver and kidney function. Twenty-three members of an NCAA Division II American football team (ages = 19-24 years) with at least 2 years of strength training experience were divided into a Cr monohydrate group (CrM, n = 10) in which they voluntarily and spontaneously ingested creatine, and a control group (n = 13) in which they took no supplements. Individuals in the CrM group averaged regular daily consumption of 5 to 20g (mean SD = 13.9 5.8 g) for 0.25 to 5.6 years (2.9 1.8 years). Venous blood analysis for serum albumin, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, bilirubin, urea, and creatinine produced no significant differences between groups. Creatinine clearance was estimated from serum creatinine and was not significantly different between groups. Within the CrM group, correlations between all blood parameters and either daily dosage or duration of supplementation were nonsignificant. Therefore, it appears that oral supplementation with CrM has no long-term detrimental effects on kidney or liver functions in highly trained college athletes in the absence of other nutritional supplements.
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