Caffeine is one of the most recognized and used ergogenic aids worldwide due to its effects on improving performance in various sports disciplines, with numerous meta-analyses indicating an improvement in endurance, muscular endurance, strength, power, etc.
In most cases, doses of 3-6 mg/kg of caffeine exert their performance benefits through various mechanisms. One of them is as an antagonist of the adenosine receptor (Figure 1), improving muscle activation, reducing the sensation of fatigue and pain. It is known that all these benefits, along with its main side effects, depend on various polymorphisms at the genetic level that influence metabolism and its action at the level of adenosine receptors (CYP1A2, AHR, and ADORA2A). In addition to other variables such as habituation to the consumption of this substance, method of intake (gum, drink, capsule…), dose, sex, menstrual cycle, nutritional status and training, timing (time of intake) and other factors at the epigenetic level.
FIG. 1 Brain-level effect of caffeine (adapted from examine.com)
A potential mechanism that is currently little explored is whether the bitter taste of caffeine mediates some of its ergogenic effects, since previous research has shown that bitter tastes (such as that of quinine) have the ability to improve performance, and this effect is mediated by bitter taste receptors in the mouth and upper gastrointestinal tract, although this may not occur at the same time.
In this way, some authors emphasize the possibility of an improvement in performance just as occurs in other similar strategies such as the use of menthol or rinsing with carbohydrates, where it seems that the sweet taste stimulates regions at the brain level through receptors in the oral cavity.
Some of the considerations of all this are that the intake of caffeine in liquid form (so that it has the same bitterness as quinine) is complicated to ingest due to its low palatability. On the other hand, sports drinks with caffeine or coffee do not have enough bitterness to provoke such responses at an ergogenic level.
Furthermore, it must be ingested and it is not enough to simply rinse the mouth, since there are receptors at the level of the digestive tract that may even be more important than those in the mouth. With all this, we find quite a few controversies in the limited existing literature, ruling out the direct improvement of performance with only rinses with caffeine solutions, even though there are adenosine receptors in the mouth and this substance can be absorbed through the oral membrane.
However, the explanation for all of this could be the limited time (10 sec) that caffeine is in the oral cavity versus at the intestinal level (45 min), so there would not be enough time to increase the caffeine concentration in plasma just by using rinses.
On the other hand, other studies dedicated to evaluating reaction time, tasks at the cognitive level, and their function during activity performance have indeed concluded with beneficial effects.
Another point to add would be the knowledge of interindividual variation in the ability to detect bitter flavors, which translates into the fact that the main ergogenic potential from a standardized dose of caffeine is due to differences in taste response (there are genetically predisposed individuals 'TAS2R GENE' with a higher number of receptors and greater sensitivity to bitter taste). Finally, it seems that some of the performance-enhancing effects of caffeine could be driven by mere expectation or placebo (since, if you give an athlete something bitter and they associate the taste with caffeine, knowing that caffeine improves performance, it will improve their performance without knowing that you have given them something that does not contain that substance).
In conclusion, according to the authors regarding this hypothesis and along with other unresolved issues concerning the use of caffeine in sports, they suggest that it is tempting to believe that we know everything about caffeine as a performance enhancer, while there is still a long way to go. Simply by uncovering some of the complexities surrounding the use of this substance, we have the potential to further improve the performance of our athletes in the coming years.
BIBLIOGRAPHY
- Pickering C. Are caffeine's performance-enhancing effects partially driven by its bitter taste? 2019;131(April).
- Pickering C, Grgic J. Caffeine and Exercise: What Next? Sport Med [Internet]. 2019;49(7):1007–30.
- Southward K, Rutherfurd-Markwick K, Badenhorst C, Ali A. The Role of Genetics in Moderating the Inter-Individual Differences in the Ergogenicity of Caffeine. Nutrients. 2018;10(10):1352.
- Pickering C, Kiely J. Are the Current Guidelines on Caffeine Use in Sport Optimal for Everyone? Inter-individual Variation in Caffeine Ergogenicity, and a Move Towards Personalised Sports Nutrition. Sport Med. 2018;48(1):7–16.
- Grgic J, Grgic I, Pickering C, Schoenfeld BJ, Bishop DJ, Pedisic Z. Wake up and smell the coffee: Caffeine supplementation and exercise performance – An umbrella review of 21 published meta-analyses. Br J Sports Med. 2019;1–9.
AUTHOR
Marcos Rueda Córdoba
- Graduate in Human Nutrition and Dietetics (UGR) and Official Master's in Nutrition in Physical Activity and Sport (UCAM). ISAK I Anthropometrist, Content creator and specialized courses in sports nutrition through online and in-person platforms. Teacher at Grupo San Valero (San Jorge University, Zaragoza)
- In-person Nutrition Consultation in Granada and online
