Friday, October 13, 2006
The author would like to highlight from the onset that this review considers caffeine in an ergogenic, or performance enhancing, role within the body. It is not intended to be used as a reference for caffeine prescription nor to reflect the role of caffeine as a dietary substance in the general public, as there are many areas where the effects differ. The author hopes this article will help to further understand the role of caffeine in sport.
Caffeine is so prevalent in modern society that it’s role as an ergogenic (performance enhancing) substance is sometimes overlooked. This article will look at how effective Caffeine is a sports supplement, how it affects the body and the ethical issues surrounding it’s continued use within the sports community. It has recently been removed from the World Anti-Doping Agency’s (WA.D.A) list of banned substances and is only a Controlled Substance by the International Olympic Committee (I.O.C) and the International Cycling Union (I.C.U). W.A.D.A is considering revising it’s decision though, after George Gregan, Australian Rugby Union Captain admitted using caffeine before games and gaining a reported 7% performance increase. As we’ll see later, many factors mean that the limit for caffeine ingestion may not prevent athletes using it or gaining significant benefits from it in competition and training.
Caffeine can be found all around us, in products ranging from beverages to over the counter medications, and it may well be the most widely used stimulant in the world today (1). So what exactly is it? The U.S National Library of Medicine lists it as a Central Nervous system stimulant that is also used in analgesic’s and respiratory system stimulants (2). It is (in scientific terms) part of a group called methylxanthines, drugs often used for respiratory illness due to their vasodilating effects.
Caffeine though is neither a typical nutrient nor is it essential for health…we can all survive without it! It is in fact a socially acceptable, legal drug consumed by all groups in society (1). So if it is non-essential for life, not produced naturally in the body and used for it’s stimulant properties why is it still treated so liberally by sporting bodies?
The answer to this may still be unclear at the end of this review but hopefully it can shed some light on what exactly caffeine does and why and whether or not it works. It is important at this point that we remember that we are considering caffeine in it’s role as a performance enhancing supplement rather than it’s role in cold medications or the everyday diet although you could argue it functions as an ergogenic aid for many there as well.
How does it actually work?
The exact reason why caffeine is such a powerful ergogenic is difficult to pinpoint and is more likely down to several different interactions on the neural and metabolic pathways in the body. Costill et al (7) originally attributed performance increases to a “glycogen sparing” effect, largely due to the increase in fatty acid metabolism that was observed with a general dose of caffeine (330mg). Later studies have investigated caffeine supplementation on a body weight basis, typically using between 3mg and 9mg per kg of body weight. Interestingly a 70kg person would have to ingest around 9mg per kg of body weight to be over the I.O.C legal limit. Many studies have shown clear effects on performance at levels beneath this (3,8,9,10,11,12,13,14).
Caffeine was for this reason originally thought of as an ergogenic aid specific to endurance based events, though recent studies have highlighted that it is not exclusive to this sort of event and can benefit shorter duration activities by reducing perceived exertion, lowering the pain response and increasing mean power output. These effects were seen in studies where the short duration of activity ruled out glycogen sparing as the method of performance increase. It is likely that Caffeine’s role in adenosine receptor antagonism may be key in it’s role as an ergogenic aid. You are probably already familiar with Adenosine as a component of ATP (Adenosine Triphosphate). Without the phosphate, Adenosine itself functions as a neurotransmitter and has been revealed as a key messenger related to sleep, it plays an important part in regulating blood flow and inhibits the release of excitatory neurotransmitters such as Dopamine (15). Caffeine works directly on the receptors for Adenosine, blocking their action on the body. This is certainly likely to play a key part in caffeine’s ergogenic function and it is now clear that glycogen sparing is not the sole (and may not be at all) mechanism by which caffeine can increase performance.
Isn’t it a diuretic?
A lot of the discussion surrounding Caffeine is about the potentially deleterious effects on the body’s hydration levels. Caffeine and methlyxanthines are listed as having a diuretic effect, and Caffeine itself is a potent diuretic (5) However whether or not this is also applies during exercise is unclear with studies by Graham et al (3) and Grandjean et al (4) contradicting this. There does not appear to be any basis for the common concern that caffeine will dehydrate your athletes (6) These findings agree with studies by Falk (16) and Wemple (17) neither of whom reported increased diuresis as a result of caffeine intake.
We should also remember that this is talking about caffeine not coffee! When the two have been compared it was found that the ergogenic effect of caffeine was largely lost when taken in as coffee, therefore we cannot extrapolate the ergogenic effects of caffeine to coffee as it would appear that the many thousands of compounds within coffee serve to negate this effect.
Perhaps one of the most insightful things to take from the study by Grandjean et al was the overall levels of dehydration across all subjects. Subjects in the study consumed an average of 1745mL but 78% of them suffered a loss in body weight through dehydration. Taking this finding in the context of the relationship between fluid and disease* in the body we might be well advised to promote more fluid intake in general for our athletes and our clients!
Of course there are other side effects besides the purported diuretic effects, caffeine can produce restlessness, headaches, insomnia, irritability, muscle twitching and arrythmias (5) These effects vary tremendously among individuals and are important to consider in a sports context where they might well contribute to an increase in state anxiety prior to or during competition.
* Michaud and colleagues conducted a prospective study over 10 years and with 47,909 participants to examine the relationship between fluid intake and disease. They determined that participants consuming over 2391mL per day had a 49% lower incidence of bladder cancer than those consuming under 1398mL.
Depending on your point of view, this is where things are a little less clear. It is well documented that benefits, often significant, can be gained from taking a caffeine supplement. It is also clear that these benefits are very evident at levels below doping regulations. However the widespread use of caffeine in society makes the classification of it complex. Most of us would agree however that taking a pure substance with no purpose other than to gain an advantage over competitors would be unethical. There may also be a deeper issue here, that acceptance of one performance enhancing substance may lead to further abuse of banned substances. Does advocating caffeine use serve to facilitate the path to more dangerous substances? By not making Caffeine a banned substance in competition is the practice of “doping” in sport being condoned? Gregan’s comment’s sparked a debate into this with several prominent figures showing their concern of the message that advocating substance use in sport can send out. Should a sports star who is a hero to many junior athletes promote using substances to increase performance? Or should he be commended for his honesty in highlighting it’s use? The effect of this is yet to be known and is surely difficult to determine but surveys tell us though, that the desire to win in an athlete is powerful, Weinberg & Gould (7) cite studies where 98% of athletes asked said they would take a performance enhancing substance if they would win and not get caught. In another survey the Canadian Centre for Drug Free Sport found that 27% of youths between 11-18 years old had used a caffeine-containing substance for the specific intent of enhancing performance. Are these youngsters therefore at higher risk of being exposed to more dangerous and damaging substances as a result of sports lenience to caffeine?
So the evidence for caffeine is clear, it is a proven and potent ergogenic substance, yet the exact reasons for this still remain somewhat equivocal. It would seem that caffeine exerts it’s effects through several different mediums both peripherally and centrally on nerves and metabolism.
Though initially regarded as an aid to performance in endurance, recent studies have demonstrated an effect across a variety of performance protocols, including short burst activities, this in part appears due to a reduced perception of pain. This review only considered studies where full-text’s were available to try to provide a clear and accurate reflection of research.
Though on several bodies controlled substance list, caffeine has been shown repeatedly to have powerful effects at levels well below the legal limit, and Conway et al (9) highlighted in 2002 that urinary doping tests may not accurately reflect the dose or plasma levels of caffeine, as so much can be dependant on individual sensitivity and the time and type of caffeine dose.
Concerns over dehydration during exercise may be unfounded as it seems that the effects of caffeine on a person at rest are not reflected during exercise, blood pressure for example will be elevated at rest after caffeine but this trend is not reflected during exercise (14).
So as an ergogenic aid, the research shows caffeine to be effective, it is relatively safe to use at levels that improve performance, it’s cheap, readily available and tolerated by most sport governing bodies. It is not without drawbacks, such as the long-term effects of supplementation, ethical issues, and the need for increasing dosage as subjects become more tolerant. These issues, combined with individual sensitivity and side effects such as palpitations, nausea, dizziness, insomnia and tremors continue to keep the debate controversial over Caffeine’s role as an ergogenic aid.
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2. http://www.nlm.nih.gov US National Library of Medicine Website
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