Summary.Creatine isused in muscle cells to store energy for sprinting and explosiveexercise. Athletes can increase the amount of creatine in muscle bytaking creatine supplements. Although some studies report noergogenic effect, most indicate that creatine supplementation (e.g.20 g per day for 5 to 7 days) increases sprint performance by 1-5%and work performed in repeated sprints by up to 15%. These ergogeniceffects appear to be related to the extent of uptake of creatine intomuscle. Creatine supplementation for a month or two during traininghas been reported to promote further gains in sprint performance(5-8%), as well as gains in strength (5-15%) and lean body mass(1-3%). The only known side effect is increased body weight. Moreresearch is needed on individual differences in the response tocreatine, periodic or cyclical use of creatine, side effects, andlong-term effects on endurance.
Reviewers' comments
Creatine is an amino acid, like the building blocks that make upproteins. Creatine in the form of phosphocreatine (creatinephosphate) is an important store of energy in muscle cells. Duringintense exercise lasting around half a minute, phosphocreatine isbroken down to creatine and phosphate, and the energy released isused to regenerate the primary source of energy, adenosinetriphosphate (ATP). Output power drops as phosphocreatine becomesdepleted, because ATP cannot be regenerated fast enough to meet thedemand of the exercise. It follows that a bigger store ofphosphocreatine in muscle should reduce fatigue during sprinting.Extra creatine in the muscle may also increase the rate ofregeneration of phosphocreatine following sprints, which should meanless fatigue with repeated bursts of activity in training or in manysport competitions.
So much for the theory, but can you get a bigger store of creatineand phosphocreatine in muscle? Yes, and it does enhance sprintperformance, especially repeated sprints. Extra creatine is thereforeergogenic, because it may help generate more power output duringintense exercise. In addition, long term creatine supplementationproduces greater gains in strength and sprint performance and mayincrease lean body mass. In this article I'll summarize the evidencefor and against these claims. I'll draw on about 42 refereed researchpapers and four academic reviews to make conclusions regarding theergogenic value of creatine supplementation. In addition, I'llprovide 25 references to studies published in abstract form, whichreport the most recent preliminary findings on creatinesupplementation.
The daily turnover of creatine is about 2 g for a 70 kg person.About half of the daily needs of creatine are provided by the bodysynthesizing creatine from amino acids. The remaining daily need ofcreatine is obtained from the diet. Meat or fish are the best naturalsources. For example, there is about 1 g of creatine in 250 g (half apound) of raw meat. Dietary supplementation with synthetic creatineis the primary way athletes "load" the muscle with creatine. Dailydoses of 20 g of creatine for 5-7 days usually increase the totalcreatine content in muscle by 10-25%. About one-third of the extracreatine in muscle is in the form of phosphocreatine(Harris, 1992;Balsomet al., 1995).
Extra creatine in muscle does not appear to increase the restingconcentration of ATP, but it appears to help maintain ATPconcentrations during a single maximal effort sprint. It mayalso enhance the rate of ATP and phosphocreatine resynthesisfollowing intense exercise (Greenhaff etal., 1993a;Balsom et al., 1995;Casey et al., 1996).
There is some evidence that not all subjects respond to creatinesupplementation. For example, one study reported that subjects whoexperienced less of a change in resting muscle creatine (<20mmol/kg dry mass) did not appear to benefit from creatinesupplementation (Greenhaff et al.,1994). However, more recent studies indicate that taking creatinewith large amounts of glucose increases muscle creatine content by10% more than when creatine is taken alone(Green et al., 1996a;Green et al., 1996b). Consequently,ingesting creatine with glucose may increase its ergogenic effect.
Researchers first investigated the ergogenic effects of short-termcreatine loading. In a typical study, a creatine dose of 5 g is givenfour times a day for five to seven days to ensure that musclecreatine increases. A control group is given a placebo (glucose orsome other relatively inert substance) in a double-blind manner(neither the athletes nor the researchers doing the testing know whogets what until after the tests are performed). Most studies haveshown that speed or power output in sprints--all-out bursts ofactivity lasting a few seconds to several minutes--is enhanced,typically by 5-8%. Repetitive sprint performance is also enhancedwhen the rests between sprints don't allow full recovery. In thiscase, total work output can be increased by 5-15%. There is alsoevidence that work performed during sets of multiple repetitionstrength tests may be enhanced by creatine supplementation, typicallyby 5-15%. In addition, one-repetition maximum strength andvertical-jump performance may also be increased with creatinesupplementation, typically by 5-10%. The improvement in exerciseperformance has been correlated with the degree in which creatine isstored in the muscle following creatine supplementation, particularlyin Type II muscle fibers(Casey et al.,1996).
Researchers have now turned their attention to longer-termcreatine supplementation. In these studies, a week of creatineloading of up to 25 g per day is followed by up to three months ofmaintenance with reduced or similar dosages (2-25 g per day).Training continues as usual in a group given creatine and in acontrol group given a placebo. Greater gains are now seen inperformance of single-effort sprints, repeated sprints, and strength(5-15%).
Table 1 at the end of this article lists thereferences to positive effects of creatine on performance.Theoretically, creatine may affect performance through one or more ofthe following mechanisms(Table 2): an increasein concentrations of creatine and phosphocreatine in resting musclecells; an increased rate of resynthesis of phosphocreatine betweenbouts of activity; enhanced metabolic efficiency (lower production oflactate, ammonia, and/or hypoxanthine); and enhanced adaptationsthrough higher training loads. Creatine supplementation duringtraining may also promote greater gains in lean body mass (see BodyComposition below).
Not all studies have reported ergogenic benefit of creatinesupplementation(Table 3). In this regard, anumber of equally well-controlled studies indicate that creatinesupplementation does not enhance: single or repetitive sprintperformance; work performed during sets of maximal effort musclecontractions; maximal strength; or, submaximal endurance exercise.What's more, one study reported that endurance running speed wasslower, possibly because of an increase in body mass(Balsom et al., 1993b).
In analysis of these studies, creatine supplementation appears tobe less effective in the following situations: when less than 20 gper day was used for 5 days or less; when low doses (2-3 g per day)were used without an initial high-dose loading period; in crossoverstudies with insufficient time (less than 5 weeks) to allow washoutof the creatine; in studies with relatively small numbers ofsubjects; and when repeated sprints were performed with very short orvery long recovery periods between sprints. It is also possible thatsubject variability in response to creatine supplementation mayaccount for the lack of ergogenic benefit reported in these studies.In addition, there have been reports that caffeine may negate thebenefit of creatine supplementation(Vandenberghe et al., 1996).Consequently, although most studies indicate that creatinesupplementation may improve performance, creatine supplementation maynot provide ergogenic value for everyone.
Although some studies have found no effect, most indicate thatshort-term creatine supplementation increases total body mass, by 0.7to 1.6 kg. With longer use, gains of up to 3 kg more than in matchedcontrol groups have been reported (seeTable 4at the end of this article for references). For example,Kreider et al.(1998) reported that 28 days ofcreatine supplementation (16 g per day) resulted in a 1.1 kg greatergain in lean body mass in college football players undergoingoff-season resistance/agility training. In addition,Vandenberghe et al. (1997) reportedthat untrained females ingesting creatine (20 g per day for 4 daysfollowed by 5 g per day for 66 days) during resistance trainingobserved significantly greater gains in lean body mass (1.0 kg) thansubjects ingesting a placebo during training. The gains in lean bodymass were maintained while ingesting creatine (5 g per day) during a10-week period of detraining and in the four weeks aftersupplementation stopped.
Findings like these suggest that creatine supplementation maypromote gains in lean body mass during training, but we don't yetunderstand how it works. The two prevailing theories are thatcreatine supplementation promotes either water retention or proteinsynthesis. More research is needed before we can be certain about thecontribution each of these processes makes to the weight gain.
In studies of preoperative and post-operative patients, untrainedsubjects, and elite athletes, and with dosages of 1.5 to 25 g per dayfor up to a year, the only side effect has been weight gain(Balsom, Soderlund & Ekblom, 1994). Evenso, concern about possible side effects has been mentioned in laypublications and mailing lists. Before discussing these possible sideeffects, it should be noted that they emanate from unsubstantiatedanecdotal reports and may be unrelated to creatine supplementation.We must be careful to base comments regarding side effects ofcreatine supplementation on factual evidence, not speculation. But wemust also understand that few studies have directly investigated anyside effects of creatine supplementation. Consequently, discussionabout possible side effects is warranted.
Anecdotal reports from some athletic trainers and coaches suggestthat creatine supplementation may promote a greater incidence ofmuscle strains or pulls. Theoretically, the gains in strength andbody mass may place additional stress on bone, joints and ligaments.Yet no study has documented an increased rate of injury followingcreatine supplementation, even though many of these studies evaluatedhighly trained athletes during heavy training periods. Athletesapparently adapt to the increase in strength, which is modest andgradual.
There have been some anecdotal claims that athletes training hardin hot or humid conditions experience severe muscle cramps whentaking creatine, and the cramps have been attributed to overheatingand./or changes in the amount of water or salts in muscle. But nostudy has reported that creatine supplementation causes any cramping,dehydration, or changes in salt concentrations, even though somestudies have evaluated highly trained athletes undergoing intensetraining in hot/humid environments. In my experience with athletestraining in the heat (e.g., during 2-a-day football practice inautumn), cramping is related to muscular fatigue and dehydrationwhile exercising in the heat. It is not related to creatinesupplementation. Nevertheless, athletes taking creatine whiletraining in hot and humid environments should be aware of thispossible side effect and take additional precautions to preventdehydration.
Some concern has been raised regarding the effects of creatinesupplementation on kidney function. The body seems to be able todispose of the extra creatine without any problem(Poortmans et al., 1997). The extra creatineis eliminated mainly in the urine as creatine, with small amountsbroken down and excreted as creatinine or urea. No study has shownthat creatine supplementation results in clinically significantincreases in liver damage or impaired liver function.
It has also been suggested that creatine supplementation couldsuppress the body's own creatine synthesis. Studies have reportedthat it takes about four weeks after cessation of creatinesupplementation for muscle creatine(Vandenberghe et al., 1997) andphosphocreatine(Febbraio et al., 1995)content to return to normal. It is unclear whether muscle the contentfalls below normal thereafter.Although more research isneeded, there is no evidence that creatine supplementation causes along-term suppression of creatine synthesis when supplementationstops (Balsom, Soderlund & Ekblom, 1994;Hultman et al., 1996).
Does creatine supplementation have undiscovered long-term sideeffects? Trials lasting more than a year have not been performed, butcreatine has been used as a nutritional supplement for over 10 years.Although long-term side effects cannot discounted, no significantshort-term side effects other than weight gain have been reported. Inaddition, I am not aware of any significant medical complicationsthat have been linked to creatine supplementation. Furthermore,creatine and phosphocreatine have been used medically to reducemuscle wasting after surgery and to improve heart function andexercise capacity in people with ischemic heart disease(Pauletto & Strumia, 1996;Gordon et al., 1995). Creatine supplementationmay even reduce the risk of heart disease by improving blood lipids(Earnest, Almada & Mitchell, 1996;Kreider et al., 1998). On the basis of theavailable research, I consider creatine supplementation to be amedically safe practice when taken at dosages described in theliterature.
Determining whether creatine supplementation has any short- orlong-term side effects is an area receiving additional researchattention. If there are side effects from long-term creatinesupplementation, an important issue will be the liability of coaches,trainers, universities, and athletic governing bodies who providecreatine to their athletes. Anyone advising athletes to take creatineshould make it clear that side effects from long-term use cannot becompletely ruled out, and that the athletes do not have to take thesupplements. It would be wise to have a formal policy for dosages toreduce the chances of athletes taking excessive amounts.
Creatine supplementation is not banned, but is a nutritionalpractice that enhances performance nevertheless unethical? Anyonepondering this question should consider that creatine supplementationis a practice similar to carbohydrate loading, which is wellaccepted. Some are also concerned that creatine supplementation couldcause a carryover effect, whereby athletes who have learned to takecreatine are more likely to use dangerous or banned substances.Proper education among athletes, coaches, and trainers regardingacceptable and unacceptable nutritional practices is probably thebest way to reduce any carryover.
A typical loading regime for a 70-kg athlete is a 5-g dose fourtimes a day for a week. Thereafter the dose can be reduced to 2 to 5g per day in order to maintain elevated creatine content. Thissupplementation protocol will increase intramuscular creatine andphosphocreatine content and enhance high intensity exerciseperformance. There is now some evidence that taking glucose (100 g)with the creatine (5 to 7 g) increases the uptake of creatine intomuscle (Green et al., 1996a;Green et al., 1996b). Consequently, Irecommend that athletes take creatine with carbohydrate (e.g. withgrape juice) or ingest commercially available creatine supplementsthat combine creatine with glucose. For athletes wanting to promoteadditional gains in lean body mass, I recommend 15 to 25 g per dayfor 1 to 3 months. Although many athletes cycle on or off creatine,no study has determined whether this practice promotes greater gainsin fat free mass or performance than continuous use. More research isneeded here.
Creatine supplements are good value. Creatine is now being soldfor as little as US$30 per kg, or about $0.60 per day when taking 20g per day. Popular sports drinks are more expensive.
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