The International Olympic Committee recognizes caffeine as one of five dietary supplements whose ability to enhance exercise performance has been clearly demonstrated. Studies have shown that caffeine consumption at doses between 3 and 6 mg/kg body mass (BM) can improve performance during efforts of varying intensity and duration. This is probably why a study published in 2019 observed that around 76% of athletes used caffeine in competition.
The main mechanism behind caffeine's performance-enhancing effect is its impact on the central nervous system, where it acts as an antagonist on adenosine receptors. This results in an increase in alertness, a reduction in perceived exertion and a decrease in perceived pain during exercise. However, individual reactions to caffeine are highly variable: around 33% of people derive no benefit from it, and some even experience a decline in performance after consuming it.
Moreover, the impact of habitual caffeine consumption on acute responses to caffeine supplementation is also a matter of debate. Some studies suggest that regular caffeine intake may reduce certain physiological responses that are typically observed during exercise immediately after caffeine intake. However, existing research on this subject is not consensual, with some studies supporting this idea and others contradicting it. And these contradictory results may be due to inconsistent definitions of habitual caffeine consumption levels among individuals and/or variations in study design, making it difficult to determine the real impact of regular caffeine consumption on physical and sporting performance. So, if you ingest caffeine daily, will you benefit from its ergogenic effects if you consume it just before a session?
To answer this question and clarify the relationship between regular caffeine consumption and the acute response to exercise following caffeine supplementation, Brazilian researchers carried out a systematic literature review and meta-analysis to determine whether this habitual consumption would influence the immediate effects of caffeine during exercise, and in what proportion.
They analyzed data from 59 studies. These studies had to use a randomized, controlled protocol and had to report participants' habitual caffeine intake. The intervention consisted of one-off caffeine supplementation, in any dose or form (capsule, tablet, drink, coffee or chewing gum), prior to exercise. A total of 1137 people were included in this meta-analysis. Of these, 958 were men and 179 women, with 718 exercising, 400 inactive and 19 classified as elite athletes.
Test efforts performed by all exercisers were classified into 3 categories: endurance (for any effort greater than 30s), strength (for any resistance training exercise) and power (for any anaerobic effort ≤ 30s). The researchers took into account the pre-exercise caffeine dose (< 3 mg/kg BM, 3-6 mg/kg BM and > 6 mg/kg BM) and whether it was lower or higher than the average daily dose of caffeine usually ingested by the participants. Finally, they also took into account the period of caffeine withdrawal before the intervention (< 24 h, 24-48 h, and > 48 h).
The main results of this study show that, overall, caffeine supplementation just before exercise has a weak positive impact on subsequent performance, whether in endurance, strength or power. And this result does not appear to be influenced by participants' usual caffeine intake. These results were equally valid for male and female participants, and for trained and untrained individuals. A positive effect was observed when the acute dose of caffeine was less than or equal to 6 mg/kg BM, but not when it was greater than 6 mg/kg BM. In addition, caffeine was found to have ergogenic effects whether the acute caffeine dose was lower or higher than the usual daily dose ingested by the participants, and irrespective of the caffeine withdrawal period.
It would appear that habitual caffeine intake does not significantly affect the ergogenic effects of acute caffeine supplementation, irrespective of gender or training status. Several studies have already shown that the beneficial effects of caffeine supplementation are similar, whatever the dose. While some research suggests that tolerance may develop with chronic caffeine use, particularly at high doses, this meta-analysis shows that performance gains are consistent whether the dose of caffeine is lower or higher than usual, up to 6 mg/kg BM. However, caution should be exercised when exceeding this dose, as side effects may occur. Overall, habitual caffeine intake may not play as important a role in exercise performance as previously thought, and athletes should be cautious about increasing their caffeine dose before exercise. Further research is needed to explore the effects of very high doses of caffeine on performance.
Whatever the daily dose of caffeine ingested, whatever the gender and whatever the level of exercisers, all benefited equally from caffeine supplementation just before an endurance, strength or power effort. Of course, response to caffeine supplementation can potentially be influenced by a number of factors other than habitual consumption, such as genetics, timing of supplementation and/or method of administration.
In addition, these results challenge the widespread notion that caffeine should be abstained from before a competition in order to maximize its effects when taken just before a performance. Significant and similar benefits were observed even when consumption was interrupted for less than 24 hours, between 24 and 48 hours or for more than 48 hours. These results concur with those of other studies showing that caffeine withdrawal of up to four days did not alter the acute benefits of caffeine supplementation for regular users.
It's also essential to bear in mind that stopping caffeine consumption can lead to adverse effects, including severe headaches, fatigue, mood disorders and concentration problems, which can affect quality of life and training. It is therefore advisable to avoid caffeine withdrawal to ensure optimal preparation for competitions.
This meta-analysis shows that caffeine supplementation prior to a competition or an important training session provides a (small) improvement in physical performance with doses of up to 6 mg/kg BM. Higher doses (> 6 mg/kg) would bring no additional benefits, and could lead to undesirable side effects (insomnia, irritability, nausea, tachycardia). Note that an espresso would contain around 122 mg of caffeine per 30 ml (of course, the concentration depends on many external factors), so for an individual weighing 75 kg, 6 mg/kg corresponds to 450 mg of caffeine, or 3.7 espressos.
Caffeine supplementation would be beneficial whatever the type of effort (endurance, strength or power), level of exercise, sex or usual caffeine intake. Habitual caffeine consumption does not appear to affect its effects on performance, enabling both low and high caffeine consumers to benefit from pre-competition caffeine supplementation without changing their daily caffeine habits. Consequently, it would not be necessary to give up caffeine before competitions, contrary to current practice. Bearing in mind that the ergogenic effect is weak, at best.
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