REVIEW OF THE FUNCTION AND EFFECTS OF CREATINE - RESULTS ARE NOT CLEAR CUT
Demant, T. W., & Rhodes, E. C. (1999). Effects of creatine supplementation on exercise performance. Sports Medicine, 28, 48-59.
This article reviews much of the scientific evidence concerning the effects of creatine supplementation. Its abstract is an excellent summary of the topic and is reproduced below.
"While creatine has been known to man since 1835, when a French scientist reported finding this constituent of meat, its presence in athletics as a performance enhancer is relatively new. Amid claims of increased power and strength, decreased performance time and increased muscle mass, creatine is being hailed as a true ergogenic aid. Creatinine is synthesized from the amino acids glycine, arginine and methionine in the kidneys, liver and pancreas, and is predominantly found in skeletal muscle, where it exists in two forms. Approximately 40% is in the free creatine form (Crfree), while the remaining 60% is in the phosphorylated form, creatine phosphate (CP). The daily turnover rate of approximately 2 g/d is equally met via exogenous intake and endogenous synthesis. Although creatine concentration (Cr) is greater in fast twitch muscle fibers, slow twitch fibers have a greater synthesis capability due to their increased aerobic capacity. There appears to be no significant difference between males and females in Cr, and training does not appear to effect Cr. The four roles in which creatine is involved during performance are temporal energy buffering, spatial energy buffering, proton buffering and glycolysis regulation. Creatine supplementation of 20 g/d for at least three days has resulted in significant increases in total Cr for some individuals but not others, suggesting that there are 'responders' and 'nonresponders'. These increases in total concentration among responders are greatest in individuals who have the lowest initial total Cr, such as vegetarians. Increased concentrations of both Crfree and CP are believed to aid performance by providing more short-term energy, as well as increase the rate of resynthesis during rest intervals. Creatine supplementation does not appear to aid endurance and incremental type exercises, and may even be detrimental. Studies investigating the effects of creatine supplementation on short term, high intensity exercises have reported equivocal results, with approximately equal numbers reporting significant and nonsignificant results. The only side effect associated with creatine supplementation appears to be a small increase in body mass, which is due to either water retention or increased protein synthesis." (pp. 49-50)
Implication. The scientific evidence surrounding the effects of creatine supplementation on performance is not supportive of the attributions given in popular culture. There is more folklore surrounding the "knowledge" about creatine and its "benefits", than objectively verified facts.
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