Creatine supplementation

Increased creatine and PCr concentrations have been achieved by giving creatine orally. The creatine dose used was 20 g daily for 4—5 days, administered in repeated 5 g doses. Muscle creatine increased by 20-40% above the preadministration content and the PCr increased by 8-15% (Harris et al., 1992). Torque generation by the knee extensor muscles was measured during five repeated bouts of 30 isokinetic MVCs, with 2 min rest periods between bouts. The exercise protocol was performed four times, before and after placebo or creatine supplementation. The total peak torque production increased significantly in all five bouts of maximal... 

Figure 4. Ten bouts of high intensity cycle exercise, each with a duration of 6 sec and with 30 sec rest periods between bouts were performed on a given day. The entire exercise protocol was performed on four separate days by each subject (n = 8), before and after placebo and creatine supplementation. Mean power output was 882 watts. Upper panels (A1 and B1) demonstrate mean revolutions per min during the 0-4 sec period of each bout and the lower panel (A2 and B2) during 4-6 sec of each bout. The left panels (A1 and A2) show results before (o) and after (x) placebo and the right panels (B1 and B2) before (o) and after (x) creatine supplementation. The study was performed in a double blind manner.

Creatine supplementation has been shown to increase the rate of PCr resynthesis in the recovery period after ischemic exercise (Greenhaff et al., 1993a). This could be attributed to an acceleration of oxidative phosphorylation by increased free creatine content available to the mitochondrial fraction of the creatine kinase enzyme, as previously suggested (Bessman and Fonyo, 1966). 

Balsom, P.D., Ekblom, B., Soderlund, K., Sjodin, B., Hultman, E. (1993). Creatine supplementation and dynamic high intensity intermittent exercise. Scand. J. Med. Sci. Sports (in press). 

Greenhaff, P.L., Bodin, K., Harris, R.C., Hultman, E., Jones, D.A., McIntyre, D.B., Sbderlund, K., Turner, D.L. (1993a). The influence of oral creatine supplementation on muscle PCr resynthesis following muscle contraction in man. J. Physiol. 467, 75 (Abstract). 

Harris, R.C., Soderlund, K., Hultman, E. (1992). Elevation of creatine in resting and exercised muscle of normal subjects by creatine supplementation. Clin. Sci. 83, 367-374. 

Whether it is possible to raise carnosine levels in human brain is unknown. One study in rats has shown that oral administration of chicken extract (a major source of carnosine in humans too) did provoke an increase in brain carnosine levels a single dose of the chicken extract led to an increase in carnosine levels within 30 min in plasma, but 1 or 2 h duration were required for increased levels of carnosine to be observed in the cerebral cortex, hypthalamus, and hippocampus (Tomonaga et ah, 2007). It is uncertain whether these effects result from direct uptake of the carnosine from plasma or a consequence of de novo synthesis. In a study using senescence-accelerated mice (SAMP8), it was found that oral supplementation with creatine provoked, at 25 weeks of age, a transient 88% increase in muscle carnosine content, accompanied by a 40% increase in anserine content, which coincided with an improvement in resistance to contractile fatigue (Derave et ah, 2008). At 60 weeks, no differences were detectable between the creatine-supplemented and control animals in terms of their muscle... 

Derave, W., Jones, G., Hespel, P., and Harris, R. C. (2008). Creatine supplementation augments skeletal muscle carnosine content in senescence-accelerated mice (SAMP8). Rejuvenation Res. 11, 641-647. 

Creatine (Cr) is one of the most widely used supplements for muscle performance enhancement. Creatine supplementation may result in an increase in muscle total Cr relative to PCr. Brault et al. investigated the ratio of PCr to total Cr (TCr=PCr+Cr) in a group of adult men using P... 

J. J. Brault, T. F. Towse, J. M. Slade and R. A. Meyer, Parallel increases in phosphocrea-tine and total creatine in human vastus lateralis muscle during creatine supplementation. Int. J. Sport Nutr. Exerc. Metab., 2007,17,624-634. 

Oral creatine supplements first gained popularity among athletes in the early 1990s following the publication of a Karolinska Institute study that found that subjects who took creatine supplements experienced a significant increase in total muscle creatine content. In theory, increased creatine stores would increase PCr stored in the muscles, which would in turn provide a larger power supply for anaerobic muscle activity and exercise (short bursts of exercise which don t require oxygen). 

Creatine was thrust onto the global athletic scene in 1992 when British sprinters Linford Christie and Sally Gunnel won Olympic gold in Barcelona after reportedly training with the aid of creatine supplementation. Since that time, a number of clinical studies have looked at both the ergogenic (output enhancing effect) and therapeutic benefits of creatine. 

Creatine monohydrate, the most popular form of off-the-shelf creatine supplementation, is an odorless, white, water-soluble powder. Its chemical name is N-(ammoimmomethyl)-N-methylglycine monohydrate. 

Creatine is sold in powdered, liquid, tablet, capsule, and chewing-gum formulations. The most popular formulation of creatine is creatine monohydrate, which is also the creatine formula that has been most extensively tested in clinical studies. Pure creatine monohydrate is a white, odorless, crystal powder with a faintly sweet taste. Other variations of creatine supplements are available, including creatine citrate and creatine phosphate. However, the clinical data on the effectiveness of these formulas is limited. 

Individuals who face extended bedrest or immobilization in order to recover from surgery may also benefit from creatine supplementation. One study, which looked at knee surgery patients in rehabilitation, found that subjects who received creatine intravenously during their recovery gained leg strength faster than those who did not. Further research published in the Archives of Physical Medicine and Rehabilitation in 2002 found that creatine supplementation improved upper body exercise capacity in patients with cervical spinal cord injuries. 

In other animal research, clinical studies have demonstrated that creatine inhibits the growth of solid tumors in rats. No data on the effects of creatine supplementation on cancer in humans had been published as of early 2002. 

Finally, creatine supplements may be useful in the treatment of heart problems. Creatine has improved exercise capacity in patients suffering from congestive heart failure, and lowered blood cholesterol in animal studies. Limited study of creatine s effect on blood cholesterol levels in healthy humans has had mixed results, with one study reporting a positive impact and another reporting no effect at all. Further research is needed to determine if creatine is beneficial in improving blood cholesterol and preventing atherosclerosis. 

Does creatine cause cancer In early 2001, the media was abuzz with reports that creatine had been linked to cancer. The story stemmed from a report issued by France s Agency of Medical Security for Food (AFSSA), which claimed that creatine posed a potential carcinogenic risk for users and urged all sports governing bodies to institute a ban of the substance. The report was allegedly based on a review of the available scientific research on creatine supplementation. But was the real science lost in translation ... 

There are no known long-term psychological effects from creatine supplementation. However, at least one study has linked the use of performance-enhancing supplements to an increased incidence of health risk behaviors. The 2001 study, which surveyed approximately 500 men and women between the ages of 17 and 35, found that study participants who took ergogenic nutritional supplements such as creatine were more likely to get drunk, drink and drive, and become involved in physical confrontations. However, since the research was limited by the fact that it involved a very specific population (subjects were new recruits entering military service), further study is needed to determine if ergogenic aids such as creatine are directly linked to an increase in these behaviors. 

However, study results have been mixed as to exactly for which activities creatine has an ergogenic effect. For example, studies involving stationary cycle sprints have demonstrated positive performance enhancing results for creatine, but it is still unknown whether these results can be consistently reproduced in actual competition outside of the laboratory. In addition, some cycling studies have not shown any significant benefit to creatine supplementation. 

Creatine supplements. Pliolo by Mark Duncan. APAVide World Photos. Reproduced by permission. 

What do home run king Mark McGwire, French tennis champ Mary Pierce, international soccer star Zinedine Zidane, British sprinter Linford Christie, and NFL tight end Shannon Sharpe all have in common All have spoken openly to the media about their use of creatine supplements in athletic training. 

Anyone with existing kidney disease, or with health conditions that put them at high risk for kidney problems (such as diabetes) should avoid creatine supplements. 

Some athletes using creatine supplements for training have reported muscle cramping and gastrointestinal distress (i.e., diarrhea, stomach cramps, vomiting), particularly with loading doses. At this time, all reports are... 

Creatine supplementation causes water retention by muscle tissue, which may be the source of muscle cramps. It has also been theorized that athletes who experience this side effect have a fluid or electrolyte imbalance due to dehydration. In some cases, adequate water intake may eliminate the muscle cramping. 

Some of the SN/AEMS incidents involved creatine monohydrate that was mixed with or taken with other supplements and substances, so it is difficult to determine to what extent creatine played a role in these reactions. There have also been anecdotal case reports of hypertension (high blood pressure) and elevated liver enzymes in athletes taking creatine supplements. 

Dehydration may also be a risk for creatine users. Creatine causes skeletal muscle to absorb intercellular fluid from bodily tissues and into the muscle where it is retained. For this reason, athletes who are already losing fluid during physical activity may be further dehydrated by creatine supplementation. 

In other independent tests, ConsumerLab.com, a privately held U.S. company that specializes in laboratory analysis of nutritional and herbal supplements for purity, strength, and truth in labeling, found that 15% of creatine supplements tested did not meet industry standards for creatine content, purity, and label claims. 

The data on the long-term health effects of creatine supplementation is extremely limited. However, at least one animal study has found that creatine caused a decline in kidney function in rats with existing renal (kidney) disease. In addition, published case reports have indicated that creatine can cause further renal impairment in people with pre-existing kidney disease. However, several studies of healthy athletes have shown that both short-term and extended creatine supplementation had no effect on kidney function. 

Creatine is not recommended for use by individuals with kidney problems, or by anyone at risk for kidney disease (such as those with a family history of kidney problems or diabetes). Again, further controlled clinical studies are needed to determine the long-term impact and safety of creatine supplement use on human renal function. 

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