Caffeine is a performance enhancing drug. If you’ve been following my articles over the last couple of years, you’ll no doubt be aware of that, because I write about it a lot. Athletes, of course, know that caffeine has the potential to enhance their performance, which is why many of them consume it prior to training and competition. Additionally, the World Anti-Doping Agency (WADA) know that caffeine is a performance enhancing drug and are, rightly, concerned about the abuse of caffeine in sport.
Table of contents
- Caffeine usage trends in sport
- Overview of research on caffeine and performance
- Key questions about caffeine and performance
- What are the wider, non-direct influences of caffeine on performance?
- How does genotype affect caffeine’s ergogenic effects?
- How does time of day affect caffeine’s ergogenic effects?
- Does training status alter caffeine’s ergogenic effects?
- Do men and women experience the same performance benefits from caffeine?
- Does habitual caffeine use alter its ergogenic effects?
- How should caffeine be utilized within repeated competitive bouts?
- Does caffeine modify training adaptations?
- How should caffeine be consumed?
- What is the optimal dose of caffeine?
- How does caffeine interact with other ingredients to influence performance?
- To what extent do placebo and expectancy explain caffeine’s ergogenic effects?
Alongside its performance enhancing effects, caffeine has the ability to harm health, having been linked to chronic issues, such as cardiovascular disease and hypertension, as well as more acute problems, such as cardiac issues, anxiety, and hyper-stimulation. As a result, caffeine was banned in competition above doses of 12 mg/mL until 2004, when the ban was removed. Very few athletes failed doping tests for caffeine (although it did happen), in part because to achieve that caffeine dose, very high concentrations of caffeine would have to be consumed. As caffeine is typically maximally ergogenic at doses of 3-6 mg/kg, this is the range most often consumed by athletes; intakes at this dose appear to correlate with urinary caffeine concentrations of 2-5 mg/mL, suggesting that doses above 12 mg/kg would have to be consumed to reach WADAs previous upper limit. Consuming this much caffeine in practice is quite difficult—the most I’ve ever consumed is 6 mg/kg, and that had some pretty nasty side effects—and, additionally, there appear to be no extra performance enhancing effects of caffeine once you exceed 6 mg/kg. Since caffeine was removed from the banned list, WADA have periodically had it placed on a monitoring list in order to determine use in athletes.
Interestingly, previous research suggested that athletes consumed similar amounts of caffeine between 2004 and 2008 as they did when caffeine was banned, suggesting that any ban was, for the most part, unnecessary. However, until a recent paper, published in the journal Nutrients earlier this year, we had no additional data regarding the use of caffeine by athletes. The latest paper throws some further light on the use of caffeine by athletes, suggesting that its use may be on the rise. To find this out, the researchers, supervised by esteemed caffeine researcher Juan Del Coso, analyzed all urine samples submitted to the antidoping lab in Madrid in the years 2004, 2008, and 2015. These samples were collected at national and international competitions held in Spain in the study years; this is important to point out, because it means that the majority of the athletes are likely to be Spanish, although there will undoubtedly be international athletes within the subjects. Overall, the researchers analyzed 7488 urine samples for their caffeine concentrations. What they found was that the median urine concentration in 2009—0.9 mg/mL—was significantly higher than the median values in 2004 and 2008; 0.7 mg/mL for both years. This suggests that, in general, athletes are consuming more caffeine. This could be for a number of reasons, but it’s likely down to an increased awareness of caffeine’s ergogenic effects, alongside the increasing number of sports supplements that contain caffeine, and the lack of any limit imposed on its use by WADA. The highest urine concentrations were found in cycling, rowing, and athletics. Interestingly, in 2008, just over 31% of samples did not contain detectable amounts of caffeine; in 2015, this number had dropped to 24.3%, demonstrating that more athletes than ever are consuming caffeine prior to competition.
There’s some added nuance to the data. At present, WADA considers caffeine concentrations above 6 mg/mL as worthy of monitoring. As mentioned earlier, such a dose is likely above the concentration that can enhance performance, and yet around 5% of athletes in the analysis from 2015 reached this threshold, although this was down from 6% in 2004. In general, the median caffeine concentration was higher in males (0.9 mg/mL) than females (0.8 mg/mL), although 65% of all urine samples with a concentration above 10 mg/mL were from females—even though females only made up around 25% of the testing pool. As a result, it’s clear that females are more likely to be consuming the largest relative doses of caffeine. The authors of this paper speculate that this is down to differences in body mass between males and females. Although researchers and nutritionists tend to think of caffeine in terms of mg/kg (e.g. 3 mg/kg), caffeine tends to be consumed in an absolute dose (e.g. 80 mg in a 250ml can of energy drink). As males tend to be heavier than females, for the same absolute caffeine dose, females are consuming a greater relative dose. For example, a can of Red Bull contains 80mg of caffeine. For an 80kg male sprinter, this is 1 mg/kg. For a 60kg female sprinter, this is 1.5 mg/kg. Add in multiple doses of this energy drink, or pre-workout, or caffeine tablets, and it’s clear to see that the scope for large caffeine doses is much higher in females.
Whilst the findings of this study demonstrate that more athletes are consuming caffeine pre-competition as a means to enhance their performance, it isn’t able to tell us about their use of caffeine pre-training, which would be an important next step for any research to explore. However, it is clear that athletes are becoming more aware of the performance enhancing effects of caffeine, and appear to be consuming slightly more of it, as a means of improving performance.
So, what does all this mean for researchers? The effects of caffeine on performance are well established and well replicated, as a recent umbrella review that I was an author on, published in the British Journal of Sports Medicine, shows. This has been established at meta-analysis level, which represents the highest level of the evidence hierarchy. Meta-analyses demonstrate that caffeine has the ability to enhance 1RM strength, vertical jump height, power output, isokinetic peak torque, muscular endurance, and aerobic endurance performance. Alongside these meta-analyses, there are additional systematic reviews which demonstrate caffeine’s performance enhancing effects on power-based sport, sport-specific endurance, and resistance exercise.
One area where the performance enhancing effects of caffeine are slightly less clear is that of sprint and repeated sprint performance; two meta-analyses have reported no effect of caffeine on these exercise types. However, individual studies, using either caffeine-containing energy drinks, or caffeine alone, suggest that caffeine has the potential to enhance performance here too. Because the performance enhancing effects of caffeine are so well established, in a recent paper, which I authored alongside Jozo Grgic (who authored the BJSM paper mentioned earlier), we suggested that there is potentially only limited benefit from further studies exploring whether standard caffeine intakes (i.e. 3-6 mg/kg/bodyweight, consumed ~60 minutes prior to exercise) enhance sporting performance. Instead, exploring the contexts and nuances of caffeine’s use might represent a more promising area for further research, allowing us to better help athletes tailor and personalize their use of caffeine to best suit their own individual make-up and needs.
Tailoring caffeine usage has been an area of particular interest to me and covered in several articles I have put together for HMMR Media:
- Are there non-responders to caffeine?
- Measuring caffeine consumption is harder than you think
- Individualizing pre-competition caffeine use
- Finding the right caffeine intake for performance
- Does Regular Caffeine Use Reduce Its Performance Enhancing Effects?
There are many questions still unanswered in this area, which I detail below.
Whilst we typically think of caffeine as a way to enhance physical performance, it also affects the brain, having a number of acute cognitive benefits. This is especially true in sleep deprived individuals; research in military troops shows that caffeine can improve attention, memory, and mood—alongside improvements in physical performance—following periods of sleep restriction, which are common during military operations. This has also been shown in the general public, and, more recently, this research has spilled over into sport. In a group of rugby players, researchers, led by Christian Cook, showed that caffeine doses of both 1 and 5 mg/kg, either alone or with creatine, reduced the loss of performance in terms of skill following deliberate sleep restriction; an important finding given that an athlete’s sleep can be reduced before important competitions due to anxiety, or during periods of multi-day competitions due to difficulty in sleeping post-competition. Caffeine also has the ability to enhance skill-based performance in non-sleep deprived subjects, suggesting that it has important psychological, as well as physical, performance benefits. These two aspects are also linked, as mental fatigue has been shown to impair physical, sport-specific, and cognitive ability in athletes; as a result, caffeine’s ability to reduce the impact of this mental fatigue is one of the ways in which it can enhance performance.
These wider aspects of caffeine deserve further exploration. Caffeine has the potential to increase anxiety, which is important for athletes to know; prior to important competitions, when anxiety is higher, athletes may need to reduce their pre-competition caffeine dose in order to reduce their anxiety. Conversely, if athletes are competing in a lower-level of competition than normal, the use of caffeine may increase their arousal similar to that of a more important competition, enhancing performance. Further research should hopefully give us some answers as to how best to use caffeine in this regard.
Returning to sleep, caffeine has the ability to increase the time taken to fall asleep, and also reduce the quality of that sleep. This effect lasts for longer than you might think, with one study showing that 400 mg of caffeine, consumed 6 hours before bed, disrupted sleep quality, reduced time spent asleep, and increased the time it took to fall asleep. This is obviously important to athletes consuming caffeine prior to taking part in an evening competition. A study in elite rugby players showed that caffeine intake prior to an evening rugby match increased the time taken to fall asleep, and reduced sleep duration and quality. There might also be a carry over here; if it takes an athlete longer to fall asleep, and reduces their sleep quality, what effect does this have on their post-competition recovery? This becomes even more important during multi-day competitions; for example, during the Olympic Games 100m runners are required to run their heats on one day, followed by the semi-final and final on the other. Might caffeine ingestion prior to the heat reduce sleep quality that night, negatively affecting performance in the semis and final the next day? It seems likely that it would, but we also have to remain pragmatic; if an athlete needs caffeine’s performance boost to qualify for the semi-finals, then it seems logical for them to still consume caffeine prior to the heats.
Caffeine might also affect recovery, both from training and competition. A recent review article suggested that cafestol and caffeic acid, two ingredients of coffee, might enhance muscle glycogen recovery, although this early research needs to be replicated. It has also been suggested that caffeine might reduce DOMS following resistance training. Conversely, caffeine might delay autonomic recovery following exercise. Further research in this area should help us better understand what, if any, effect caffeine has on post-exercise recovery, better informing our use of this ergogenic aid.
In 2017, I authored a paper exploring the inter-individual effects of caffeine on performance, detailing how research suggests that two genes, CYP1A2 and ADORA2A, might affect how ergogenic an individual finds caffeine. CYP1A2 encodes for an enzyme called Cytochrome P450 1A2, which is responsible for metabolizing caffeine. Variation in this gene appears to alter how much of this enzyme you can produce; individuals with the AA genotype tend to produce more, and as such metabolize caffeine quicker than AC and CC genotypes; as a result, they’re often termed “fast metabolizers”. A study from last year, with 100 subjects, showed that 4 mg/kg of caffeine enhanced endurance performance in AA genotypes, had no effect in AC genotypes, and actually made performance worse in CC genotypes. Other studies have reported similar results, although others show either no effect, or the opposite effect. As such, we need further research, especially with increased sample sizes (similar to that in the Guest study) to determine the true effect of CYP1A2 on caffeine’s ergogenic effects. Additionally, as I wrote last year, it strikes me as unlikely that caffeine cannot enhance performance in CC genotypes; perhaps they just need a different dose, or to consume caffeine a greater amount of time prior to exercise.
Other genetic variants will no doubt affect caffeine’s ergogenic effects. One promising gene for study is ADORA2A, which encodes for a type of adenosine receptor. A single study suggests that TT genotypes appear to find caffeine more ergogenic, although more research is certainly required to replicate this finding. Additionally, there is the potential for variation in genes found within the serotonin, dopaminergic, adenosine, and adrenergic systems (such as HTR2A, DRD2, COMT, AMPD1, ADRB1, ADRB2 and ADRB3) may affect the performance benefits each individual may gain from caffeine; hopefully further research will shed additional light on this.
As anyone who has travelled across time zones and suffered the associated jet lag will know, our bodies have an ingrained circadian rhythm. We’re now starting to better understand how this rhythm might affect performance, with research suggesting that strength and power appears to peak in the evening. Athletes often have to train, and even compete, in the morning; can caffeine be a way to offset this circadian variation in performance?
A few studies have explored this. Mora-Rodriguez and colleagues demonstrated that caffeine ingestion prior to a morning session increased performance to that of an evening session, and, in a second study, enhanced performance in the morning but not the evening. This has also been shown in terms of aerobic endurance performance. Given that we know caffeine is an effective aid in limiting the effects of jet lag, and can even possibly help in retraining the body’s circadian rhythm, it does seem possible that caffeine may assist in offsetting any circadian rhythm-based loss of performance; hopefully further research will better help us to understand this area.
An early research paper, published in 1992, explored whether caffeine’s ergogenic effects varied between trained and untrained subjects. In that study, both trained and untrained swimmers consumed caffeine or placebo prior to a swimming time trial, and only the trained swimmers demonstrated a performance improvement with caffeine ingestion. A similar study, this time in cyclists, reported that experienced trainers showed a performance improvement with caffeine, whilst merely “active” individuals did not.
The reasons for this potential variation in performance benefits between trained and untrained subjects is currently unclear. In her seminal caffeine review, Louise Burke suggested that trained individuals likely exhibit less natural variation in performance, and so, as a result, find caffeine ergogenic, whilst in untrained subjects the larger natural performance variation obscures any performance benefit from caffeine. Additionally, one of the ways that caffeine works is by binding to adenosine receptors—this is why variation in ADORA2A, which encodes for an adenosine receptor, might impact performance. Some studies suggest that trained individuals have an increased number of adenosine receptors, which might be another mechanism through which trained subjects see increased performance benefits from caffeine.
However, other results from research in this area suggest that training status doesn’t affect caffeine’s ergogenic effects, which is why we need more research here; by better understanding this, we can tailor our advice to active individuals depending on their training status.
The vast majority of the research around caffeine in sport has utilized male subjects. One of the potential reasons for this is that females may experience differences in caffeine metabolization speed at different stages of their menstrual cycle, or through oral contraceptive use, representing a potential confounder for researchers to control for, increasing the difficulty of deriving firm conclusions. Whilst a number of studies clearly show that caffeine is ergogenic for females, it’s not clear whether caffeine is as ergogenic for females as it is for males.
Earlier this year, a group of researchers from Australia recruited both males and females to a study, giving them either 3 mg/kg of caffeine or placebo 90-minutes prior to a cycling performance test. Both males and females exhibited roughly the same size of improvements from caffeine (around 4%), suggesting that caffeine affects males and females to the same extent, although we need further research to explore this further and confirm these early findings.
Late last year, I authored a paper titled What should we do about habitual caffeine use in athletes? In that paper, my co-author John Kiely and I examined the research around the impact of regular caffeine use on caffeine’s subsequent ergogenic effects. This is obviously an important consideration for athletes; if they regularly consume caffeine pre-training, does this limit the performance improvement they might see from caffeine pre-competition? Overall, we found that there were very few studies in this area, and we came to a tentative conclusion; that regular caffeine intake appears not to negatively affect the pre-competition performance enhancing effects of caffeine, provided that the pre-competition caffeine dose is higher than the habitual dose.
A more recent study has shed some additional light on this. Here, the authors recruited eleven subjects, three women and eight males, into a randomized, double-blind, placebo-controlled, cross-over experimental design. The subjects underwent two identical protocols, therefore acting as their own controls, which, because the subject is their own control, removes common confounders such as genetic variation and differences in environment. Both protocols were twenty days in duration; in one, subjects ingested 3 mg/kg of caffeine per day, and in the other a placebo. On three occasions each week, the subjects underwent a maximal cycle test, along with a 15 second all out cycle sprint. The results showed that, when compared to placebo, caffeine enhanced performance in the exercise tests on each day it was consumed. However, the size of the improvements from caffeine were reduced as the experiment progressed. On day one, caffeine had a “large effect” on exercise performance when compared to placebo (effect size [ES] = ~1.7), whilst on day 6, this had reduced to an ES of 1, and the further degraded to around 0.7 by day twenty, which is termed as a “moderate” effect size. These results held true both for the maximal cycle test, and the sprint cycle test. As such, whilst regular caffeine intake does not appear to remove caffeine’s ergogenic effects, it does appear to reduce them, at least in this study.
So, does regular caffeine use affect its performance enhancing effects? At present, it’s difficult to say for sure, which is why it’s important to research this area further – especially as athletes tend to also consume caffeine outside of exercise contexts, such as in social situations via coffee, tea, or soft drinks.
In caffeine research, the most common type of design is for subjects to consume caffeine about 60 minutes before a single exercise test, in which the researchers determine whether or not caffeine enhanced performance. However, this doesn’t necessarily mimic what athletes have to do in real life; in many cases, athletes are required to have two competitive bouts very close together. In my career, for example, it was a fairly frequent occurrence to have the semi-final and a final of a race within an hour or so of one another, especially at Grand Prix meetings. Because the half-life of caffeine is around 4 hours—much longer than the break between competitive bouts—it remains unclear whether a second dose of caffeine would be advantageous in these situations. Furthermore, because caffeine can enhance performance, there is the potential that fatigue might be higher following the first competitive bout, reducing performance in the second bout. These aspects are poorly explored and understood, as identified by Louise Burke in an excellent 2017 paper.
A small handful of studies have explored this. In one, researchers found that ingestion of 5 mg/kg of caffeine before morning exercise did not negatively affect the performance benefits seen following ingestion of 2.5 mg/kg six hours later. Interestingly, performance was also maintained if caffeine was not ingested prior to the second exercise bout, suggesting that re-dosing was perhaps unnecessary. A more recent study explored the effects of single (either 10 mg/kg or 4 mg/kg) or repeated (5 x 2 mg/kg) caffeine doses on five simulated wrestling performances separated by 45-180 minutes. The 10 mg/kg caffeine dose only improved performance in the first bout; the 4 mg/kg dose had no ergogenic effect; whilst the repeated dosing strategy enhanced performance in four out of the five performance tests. Given these conflicting results, and the lack of research in this area, further research would hopefully be very fruitful.
Because caffeine can enhance performance, there is the potential that it might assist in increasing the improvements seen from a training program. In short, we just don’t know. We know that, acutely, caffeine can increase the training load carried out in a resistance training session, which suggests that, if this improvement were maintained across sessions, that training adaptations would be greater, but whether or not this is maintained is unclear. Further research here would be hugely impactful, both for athletes—where training improvements are likely linked to performance benefits—but also for the general public, where increases in training adaptations could well have a large effect on the risk of various different types of diseases.
Typically, if we look at caffeine research, caffeine is consumed in its anhydrous, powdered form, most often in a capsule or tablet. Again, this doesn’t necessarily mirror how athletes utilized caffeine in practice, which can include coffee, caffeinated energy drinks, caffeinated energy bars and gels, and caffeinated gum, as well as some more experimental methods, such as caffeinated nasal sprays. Some more recent research has explored caffeine mouth rinses, where the caffeine itself is not ingested. As such, there are a multitude of different methods by which caffeine can be ingested; whilst most are not that well explored, each brings their own separate nuance and context regarding their use.
The best research article to date on the topic of alternative methods of caffeine ingestion was published in 2018, and authored by Wickham and Spriet. In their review, the authors summarized research on many of the different methods in which caffeine can be ingested, demonstrating the often limited evidence behind each. For example, only two studies had explored the use of caffeinated gels on performance, which, whilst promising, require further work to determine the optimal dosing and timing strategies. This latter point is important, as caffeine consumed through many of this alternative forms is often absorbed quicker than powdered caffeine; for example, caffeinated chewing gum can increase plasma caffeine concentrations in around 15 minutes. This could be useful when a rapid caffeine hit is required, such as during the half-time period in team sports, and other non-ingestion methods, such as a caffeine mouth rinse, might be effective at reducing some of the negative gastro-intestinal effects of caffeine during exercise. As research in this area develops, hopefully more specific guidelines for each type of caffeine ingestion method can be developed.
Coffee deserves a special mention, as it represents the method of caffeine ingestion utilized by most of the world’s population on a daily basis. Coffee appears to be ergogenic, which is unsurprising given its caffeine concentration, but the question is whether it is as ergogenic as caffeine in isolation. In an early review, Trevor Graham, when summarizing the results of five studies, concluded that coffee was “probably inferior to caffeine as an ergogenic aid”. However, more recent research suggests this might not be the case; here, researchers reported that both caffeine on its own, and caffeinated coffee, both standardized to deliver a caffeine dose of 5 mg/kg, were similarly effective in improving aerobic endurance exercise; similar results have been reported for strength and sprint performance. As such, it appears that caffeine and coffee are equally effective, providing the dose is matched. However, there are some practical considerations surrounding the use of coffee as the method of consuming caffeine. Firstly, to get a dose of around 5 mg/kg of caffeine from coffee, it’s likely that an average male would have to consume around 4-5 cups of coffee, which is a lot of liquid. An additional complication is that the dose of caffeine within coffee is highly variable, differing both between blends and brands, and within the same brand across time. As such, it’s difficult to know what caffeine dose you’re actually getting from coffee, although this is a problem that affects many caffeinated products. Furthermore, coffee tends to be consumed whilst warm, which could affect thermoregulation, especially during exercise in hot temperatures, and represents a practical issue; coffee has to transported to the competition venue in a container that maintains its temperature, and requires access to boiling water to prepare. As such, coffee is perhaps impractical for use as the main source of caffeine ingestion, especially around competition, although for athletes in a more relaxed training environment, it still could be useful.
Whilst it’s clear that caffeine enhances performance, a logical additional question to ask is “what is the optimal caffeine dose to use?” At present, it appears that we don’t have a clear answer to this question. In general, it appears that very high doses of caffeine (i.e. above 9 mg/kg) offer no additional performance benefit compared to doses of around 6 mg/kg, so it isn’t a case of more caffeine is better; in a study comparing 3, 6 and 9 mg/kg of caffeine, only the lower two doses enhanced performance in an endurance test. Furthermore, there appears to be no difference in performance with doses of 3 and 6 mg/kg when it comes to endurance performance. When it comes to high intensity exercise, however, the results are less clear. One study showed that 5 mg/kg was more effective than 2 mg/kg at increasing torque, whilst another demonstrated that 9 mg/kg enhanced contraction velocity to a greater extent than 3 and 6 mg/kg. Conversely, a recent study showed that doses of 2, 4 and 6 mg/kg were equally effective at improving lower body strength when compared to placebo, whilst for upper body strength, only a dose of 6 mg/kg was effective.
One of the problems here is that the individuals comprising these studies likely had different genotypes, which, as discussed earlier, might affect the optimal caffeine dose. Additionally, different exercise types might rely on different caffeine mechanisms to enhance performance, and these mechanisms may require a different dose of caffeine in order to occur. As a result, the optimal caffeine dose is likely to be individual and task specific; there can be no one-size fits all recommended dose. This is why further research exploring the impact of individual factors on caffeine’s ergogenic effects is important; by understanding these factors, we can do a better job of personalizing an individual’s caffeine strategy.
Whilst the ergogenic effects of caffeine are well-established, caffeine is often co-ingested with additional ingredients, such as, in the case of sports drinks, carbohydrates and taurine. These additional ingredients may themselves have ergogenic effects; for example, carbohydrates are a well-established ergogenic aid, and a recent review reported improvements in endurance performance following ingestion of a single taurine dose. However, relatively few studies explore the effects of ingestion of multiple ergogenic aids together on performance. In seeking to understand the combined effects of multiple ingredients, ideally studies should compare each ingredient individually to placebo, and then the effects of combined ingestion compared to ingestion of each ingredient in isolation. Recently, Louise Burke reviewed studies meeting such criteria and conducted in athletes, reporting conflicting results. For example, when caffeine and phosphate were combined, the ergogenic effects were smaller than when phosphate was consumed in isolation, although in both these studies, caffeine, when consumed in isolation, was determined to offer no ergogenic benefit, which is a potential confounder. When combined with beetroot juice, the ergogenic effects of caffeine were potentially reduced, whilst the results surrounding caffeine and bicarbonate co-ingestion are conflicting. Additionally, in a recent meta-analysis on caffeine-containing energy drinks, it was concluded that such drinks improved performance across a variety of exercise modalities, although the authors identified taurine, and not caffeine, as they key ergogenic ingredient in this case, a result replicated elsewhere.
It’s clear that a better understanding of the combined ergogenic effects of caffeine and other co-ingested ingredients is important, especially given the wide availability and use of multi-ingredient energy drinks and supplements; although such investigations are methodologically challenging, greater insights in this area will lead to more informed decisions regarding the use of caffeine-containing multi-ingredient ergogenic aids.
Alongside caffeine’s well-established physical effects, it also exerts beneficial changes in psychological traits, including that of mood, motivation, and determination. As a result, there is the possibility that at least some of caffeine’s ergogenic effects are driven by placebo and expectancy effects. This was demonstrated in an interesting paper from 2006, where researchers recruited six well-trained male cyclists to baseline and experimental 10-km cycle time trials. In the experimental trials, the subjects were informed they were consuming varying doses of caffeine (0 mg/kg [i.e. placebo], 4.5 mg/kg, and 9 mg/kg), whilst, in actual fact, all trials were carried out under placebo conditions. When the subjects believed they had consumed caffeine, they demonstrated a 2.2% increase in mean power compared to baseline, and there was a dose-response relationship in that performance improved to a greater extent when subjects believed they had consumed the higher dose of caffeine. Similar findings have been reported, which were summarized in a recent review. In this review, the authors reported potential expectancy effects of caffeine in 13 out of 17 identified studies, suggesting that if an individual believes they have consumed caffeine, and believes that caffeine is ergogenic, they are likely to experience a performance benefit, even if caffeine has not been consumed. Similarly, the correct identification of placebo appears to reduce performance – i.e., if you know you’ve consumed a placebo as opposed to caffeine, your performance is often worse.
Using this information in practice has obvious practical considerations. The deceptive ingestion of placebo in place of caffeine in athletes may have performance benefits if caffeine increases the risk of performance-limiting negative side effects, such as increases in gastro-intestinal distress or anxiety, but this is only true if the athlete believes they have consumed caffeine. When athletes correctly identify that they have consumed placebo, performance appears to be reduced. As such, the use of such deceptive practices by coaches and/or support staff may backfire. Furthermore, the deceptive administration of placebo is ethically troubling, as athletes likely cannot give true informed consent to such a practice.
The findings of the studies discussed here also have important considerations for future research on caffeine and exercise. Whether an individual believes caffeine can enhance performance may change their exercise performance, irrespective of whether they have actually consumed caffeine. Similarly, the correct identification of administration of caffeine or placebo can modify performance. As a result, researchers should attempt to control for caffeine expectancy in intervention studies, and also collect data as to the effectiveness of their blinding procedure. Further research in this area is crucial to better understand the impact of prior expectancy on caffeine’s ergogenic effects, as well as some of the individual drivers of this expectancy, such as genotype and prior experiences, and, potentially, taste, given that caffeine is a bitter compound and that correct identification via taste may impact performance. As knowledge is this area grows, clearer guidelines on if, and how, to utilize this information in practice may become apparent.
Whilst it’s clear from the research that caffeine can enhance performance—and we know that athletes know this, because they’re taking more than ever—the challenge now is to explore the nuance and contexts surrounding the use of caffeine as a performance enhancer in order to better enhance athletic performance. Some of the aspects identified by Jozo and myself in our paper, and detailed above, should help, especially as more research evolves and develops in this area. There is also an increased need for sports-specific research on caffeine; at present, the majority of caffeine research explores its impact on single physiological traits, such as strength and endurance; future research will hopefully explore how improvements in these areas affects actual performance in specific sports. Research in this area is emerging, with studies exploring the impact of caffeine on basketball, swimming, rugby, soccer and volleyball performance, with hopefully more on the way. As a result, whilst it’s tempting to believe that we know all there is to know about caffeine in sport, this couldn’t be further from the truth, and the next decade of caffeine research promises to be as exciting as ever.