American Fitness Professionals & Associates

By Jeff EdmundsThe purpose of this article is simply to inform the reader of the basic principles and foundations behind creatine and its supplementation. Its popularity is evident and likely a result of the fact that, short of macronutrients, it is one of the most researched exercise nutrition supplements to date; this compound actually has been shown in well-controlled scientific studies to be quite effective in producing desired results, unlike many, many other “supplements” widely available to the
unwary athlete these days. I do not discuss more advanced research nor supposed detriments and myths associated with creatine supplementation, as this will cross beyond the scope of a basic explanation of this compound and its effects. I will address these issues in another section. 

A Brief Description

Creatine is a naturally occurring, key component of the energy compound creatine phosphate, whose importance in muscle contraction has been apparent since the early 1900’s (1). Creatine synthesis initiates in the kidney, where two amino acids, arginine and glycine, react to form guanidinoacetate (an amidine group is reversibly transferred from arginine to glycine to form this acid). This compound is transported to the liver, where a methyl group is irreversibly transferred from -adenosylmethionine to guanidinoacetate to form methyl guanidine-acetic acid, otherwise known as creatine. Once synthesized, creatine is transported to the blood stream and enters the muscle tissue by an active
mechanism against a concentration gradient, depending on extracellular sodium ions and metabolic energy (2). In the muscle, it is phosphorylated by adenosine triphosphate (ATP), forming creatine phosphate, or phosphocreatine. I bother to describe this process in relative detail so the origin of this compound is clear - it is a purely natural substance that the body already makes (endogenous) from
existing internal constituents. 

Function: The Creatine Phosphate Energy Pathway

When a muscle becomes active (i.e., it contracts), phosphate groups from adenosine triphosphate (ATP) molecules are liberated, and the resultant energy is used to fuel the movement (forming adenosine diphosphate, ADP); however, the free ATP pool in muscle tissue can suffice only for a very short period. Thus, during contractile activity, creatine phosphate transfers a phosphate group
(catalyzed by magnesium ions and creatine kinase) to ADP, thereby reforming ATP, providing further energy for muscular activity. What does all this scientific “mumbo-jumbo” mean? Simple. Creatine phosphate is basically an essential storehouse for energy, which provides for muscular contraction to continue past the handful of seconds ATP allows; without it, we would be severely limited in our ability to sustain extended periods of intense physical activity.

Creatine Supplementation

It has been hypothesized that supplementing the diet with additional creatine may enhance muscular contraction (at least for short periods) and therefore performance. Basis for this lies within the assumption that additional creatine will be added to the existing pool in the muscle, which will allow for more creatine phosphate to be produced (resynthesized) and eventually be drawn upon for
energy during intense muscular action. Due to the nature of creatine’s function, it can be assumed that enhancing its muscular pool concentration will noticeably affect only those activities that rely heavily upon this anaerobic energy pathway.

In other words, endurance activity, which relies primarily on aerobic methods of energy production, will not benefit from creatine supplementation. Studies performed examining creatine’s ergogenic effects on endurance activity have shown this to be true (3). It can also be extrapolated in a limited fashion from existing studies that creatine supplementation is most effective in improving
performance in activities with particular rest-to-work ratios. Since an accelerated rate of creatine phosphate resynthesis in the muscle is frequently suggested as the primary mechanism to explain exercise performance improvement following creatine supplementation (4), ingestion of this compound may only be significantly effective during activities with uneven rest-to-work ratios. For example, running has a rest-to-work ratio of approximately 1:1, meaning the rest phase is roughly equal to that of the work phase. Exercises such as football, basketball, rowing, or weight lifting have greater ratios (at least 2:1).

Since greater time is spent in the rest phase during the latter activities, it can be assumed that greater creatine resynthesis will occur, allowing more room for benefit, according to this hypothesis.

While it is possible to obtain sufficient creatine in the diet, it would be necessary to consume approximately 2.4 pounds of raw beef per day to receive an average maintenance dose of creatine (5 grams) (heating severely reduces creatine’s bioavailability) (5). It is necessary to “load” the muscle with exogenous creatine for a period of time in order to sufficiently saturate you body’s capacity.
A relative recommendation for a typical loading phase would be to consume 285 mg/kg body weight/day (usually spaced into 5 equal servings) for 5 to 7 days (6). A more general recommendation would be to consume 5 grams, 4 to 5 times per day for 5 to 7 days. This has been shown to be sufficient in “maxing out” the muscles’ creatine phosphate storage ability, after which a maintenance dose schedule of 28.5 mg/kg body weight/day, or more generally 2 to 5 grams/day, should be undertaken to sufficiently sustain these elevated muscle creatine pools. Intake of this compound at this rate has indeed been shown to increase muscular strength during brief, intense exercise during numerous controlled trials (7,8).

It has also been noted that creatine supplementation increases muscular water retention (dubbed “cell volumizing”), likely due to fluid being transported into the cells with creatine (the immediate weight gain experienced with initial creatine supplementation is due to this water retention)(9). This is not standard water retention, as the fluid actually is contained within the cells, and therefore is much less likely to fluctuate as extracellular fluid does. Intracellular water accumulation promotes a fuller look to the muscles, in contrast to the puffy, bloated appearance associated with extracellular retention.

It has been noted that only ~20% of subjects who ingest creatine alone have an increase in muscle content approaching the maximal total concentration of 160 mmol of creatine/kg dry muscle (6). In fact, around 20 to 30% of people do not respond to creatine supplementation at all (

However, it has been shown that individuals who ingest creatine in solution combined with simple carbohydrates (~370 g/day), such as with a juice or sport drink, can increase their muscle creatine accumulation by 60%, including those who do not respond to solitary creatine consumption (10, 11). This may be attributed to the enhanced insulin flux associated with simple carbohydrate ingestion. Insulin shuttles carbohydrates (and fatty acids) into muscle cells, and it can be assumed creatine is taken up much more efficiently with greater quantities of this hormone circulating.

Conclusion

While clearly not everything is known about creatine or its supplementation, a plethora of support suggests it to be a safe, relatively inexpensive, and effective supplement when used appropriately. No long-term examinations of creatine ingestion have been completed (though I believe such testing is currently under way), so it is obviously impractical to definitively suggest this compound’s
extended effects or detriments on the body and/or performance. However, it can, at this point, be relatively safely predicted that this is one sport nutrition supplement that indeed enhances intense muscular action with negligible-to-non-existent side effects.

It should be noted that I strongly advise that any individuals with renal    insufficiency or omplications of this nature not participate in the use of this supplement.   

References

1. Hunter, A. (1922). The physiology of creatine and creatinine. Physiology Reviews, 2: 586-599.
2. Guimbal, C. and Kilimann, M. W. (1993). A Na+-dependent creatine transporter in rabbit brain, muscle, heart, and kidney. The Journal of Biological Chemistry, 286(12): 8418-8421.
3. Engelhardt, M. Neumann, G., Berbalk, A., and Reuter, I. (1998). Creatine supplementation in endurance sports. Medicine and Science in Sports and Exercise, 30(7): 1123-1129.
4. Terrillion, K. A., Kolkhorst, F. W., Dolgener, F. A., and Joslyn, S. (1997).
The effect of creatine supplementation on two 700-m maximal running bouts. International Journal of Sport Nutrition, 7(2): 138-143.
5. Passwater, R. A. (1997). Creatine: Enhancing muscular function, this safe, natural dietary supplement helps athletes achieve better performance and strength quickly. Keats Publishing, Inc.: New Canaan, CT.
6. Greenhaff, P. L. (1997). The nutritional biochemistry of creatine. Journal of Nutritional Biochemistry, 8: 610-618.
7. Greenhaff, P. L., Casey, A., Short, A., H., Harris, R., Soderlund, K., and Hultman, E. (1992). Influence of oral creatine supplementation on muscle torque during repeated bouts of maximal voluntary exercise in man. Clinical Science, 84: 565-571.
8. Earnest, C. P. Snell, P. G., Rodriguez, R., Almada, A. L., and Mitchell, T. L.
(1995). The effect of creatine monohydrate ingestion on anaerobic power indicies, muscular strength, and body composition. Acta Physiol Scand, 153: 207-209.
9. Harris, R. C., Soderlund, K., and Hultman, E. (1992). Elevation of creatine in resting and exercised muscle of normal subjects by creatine supplementation. Clinical Science, 83: 367-374.
10. Green, A. L., Simpson, E. J., Littlewood, J. J., Macdonald, I. A., and Greenhaff, P. L. (1996). Carbohydrate ingestion augments creatine retention during creatine feeding in man. Acta Physiol Scand, 158: 195-202.
11. Green, A. L., Hultman, E., Macdonald, I. A., Sewell, D. A., and Greenhaff, P. L. (1996). Carbohydrate ingestion augments skeletal muscle creatine accumulation during creatine supplementation in man. American Journal of Physiology, 271: E821-E826.