Caffeine supplementation for soccer: A review of strengths, limitations and knowledge gaps

Abstract

Caffeine is a well-established ergogenic aid with a wealth of evidence demonstrating beneficial effects for physical performance, cognitive function and sport-specific skills. Intuitively, it may be considered that such effects may translate to improved soccer specific performance, however, evidence examining the effects of caffeine on the interacting demands of soccer match play is sparse. Given that caffeine supplementation is highly prevalent in professional soccer, and in a number of cases practices adopted lack supporting evidence, this review evaluates the current state of the knowledge regarding the ergogenic potential of acute caffeine consumption specifically for soccer performance. Furthermore, this review identifies knowledge gaps to guide future research, and whilst considering the unique environmental constraints, uses the available evidence to develop practical guidelines for safe and effective use.

Keywords

Ergogenic Aids - Football - Performance - Sports Nutrition

Introduction

Caffeine is a well-established performance-enhancing supplement with benefits from acute consumption demonstrated across several facets important to sports performance. The wealth of literature has been summarised in several meta-analyses which demonstrate small but significant caffeine-induced improvements in aerobic endurance performance,[1] [2] [3] [4​] muscular strength and power,[5] [6] [7] [8​] anaerobic power,[9​] and cognitive functions.[10​] Such outcomes represent important facets of soccer match play and whilst it might seem reasonable to infer that these benefits may translate to improved soccer performance, evidence examining the specific and interacting demands of soccer match play is sparse.

Attributable to what may appear to be overwhelming evidence and the highly commercialised potential of caffeine in the sports supplement market, caffeine consumption for the purpose of improved performance in commonplace. Specifically, a recent survey of elite soccer teams in England indicated that 97% of teams sampled provided caffeine to players to improve performance.[11​] As such, a review of this topic is particularly pertinent given the prevalence of caffeine use, and apparent limited translation of caffeine administration procedures advocated in research to practice.[11​]

The bioavailability of caffeine is high and nearly all ingested is absorbed in the stomach (20%) or gastrointestinal tract (80%) before entering the bloodstream.[12] [13​] Caffeine is both hydrophobic and lipophilic, and as such, easily and rapidly transverses biological membranes resulting in wide distribution throughout the body, including diffusion across the blood–brain barrier.[13​] Mechanisms underpinning the ergogenic potential of caffeine have been the subject of previous reviews,[13] [14] [15​] and in the most part have been attributed to the action of caffeine as a central adenosine receptor antagonist particularly at A1 and A2a subunits.[16​] Such effects result in an increase in excitatory neurotransmitters,[17] [18] [19​] resulting in increased motor unit firing, improved neuromuscular function, increased arousal and alertness, suppressed pain and reduced fatigue.[15] [20​] Furthermore, at physiologically relevant doses, caffeine may act directly on the muscle, augmenting processes involved with excitation-contraction coupling, resulting in increased muscle power output.[21​] These interacting mechanisms likely account for the influence of caffeine on sports performance.

Soccer is a highly dynamic sport requiring complex interplay between physical, technical and tactical proficiency which are underpinned by neuromuscular, cognitive and emotional function.[22​] [23] [24] [25] [26​] Studies evaluating the ergogenic potential of caffeine for soccer performance considering the complex demands of match play are limited, and subsequently influence the development of safe and effective guidelines for use. This review aims to evaluate the current state of the knowledge regarding the ergogenic potential of acute caffeine consumption specifically for soccer performance. Specifically, this review will critique the evidence regarding the effects of caffeine supplementation on physical and cognitive facets important for soccer performance; evaluate caffeine effects on technical and tactical outcomes and match play; identify knowledge gaps and limitations in the application of research findings to soccer-specific practice; and based on the available evidence, produce recommendations to athletes and practitioners.

Effects of caffeine on soccer-specific physical performance

Attributable to the advancement in sports technology, the physical and energetic demands of soccer match play have been well characterised, and the intermediate nature of the sport has a complex physiological demand being highly taxing on both the aerobic and anaerobic energy systems.[23​] However, given a myriad of factors (e.g., opposition, environment, formation, and tactics), greater physical performance is not always associated with match outcome,[27] [28​] although it is evident that physical capability is an essential facet of performance that distinguishes between elite and sub-elite players[29​] and provides the basis for execution of the chosen match strategy. Furthermore, several indirect links between physical performance and facets that may underpin success exist. Specifically, in the 2007/2008 German Bundesliga, 83% of goals in the latter half of the season involved at least one power action from the scoring or assisting player, defined as sprint, jump or change of direction (CoD) speed.[30​] Moreover, evidence suggests that covering greater distance and increased frequency of high-intensity runs when in ball possession results in more goal chances, shots, shots on target, passing and passing accuracy, crosses, and a successful high press in elite soccer players.[31​] As such, small increases in physical ability induced by caffeine consumption could be beneficial to athletes.

Interestingly, two relatively recent systematic reviews have evaluated the effects of caffeine supplementation on physical performance in soccer players and report conflicting outcomes.[32] [33​] Such conclusions were based on 16 and 17 studies, respectively, with the most recent review being published in 2021. Whilst there have been several recent publications that may allow for a more precise summary, for the most part, studies specific to soccer evaluate acute caffeine effects in well-established physical performance tests (e.g., vertical jump, straight-line sprint speed, CoD​​​​​​ performance, and repeated sprint performance) in elite and sub-elite soccer players across different ages.[34​] [35] [36​] There is no reason to believe soccer players would respond to caffeine differently than athletes in other sports; therefore, it is prudent to evaluate the ergogenic potential of caffeine on relevant well-established performance tests more broadly considering the wealth of published work that has reported effects on these assessments before evaluating literature employing soccer-specific tests.

Vertical jumps are an indicative measure of lower limb power and have some sports-specific relevance. The ergogenic effects of caffeine on vertical jump performance (mainly countermovement jump [CMJ] and squat jump) have been thoroughly assessed, with the weight of evidence suggesting small but significant benefits across a range of athletic populations.[37​] Furthermore, unlike other physical performance measures, there is a growing body of work demonstrating that caffeine doses lower than 3 mg·kg⁻¹, and as low as 1 mg·kg⁻¹, have been shown to improve CMJ height.[36] [38​] However, in a study by Ellis, Noon, Myers and Clarke, [36​] only 3 mg·kg⁻¹ was effective in improving the CMJ performance of elite youth soccer players both pre- and post-exercise. Whilst the CMJ challenges biomechanical constraints that underpin performance in other vertical jumps, it should be considered that bipedal standing vertical jumps do not represent the more complex jumping strategies used in soccer match play.

Elite outfield players cover 22–24% of total match distance at high-intensity speeds greater than 15 km/h and 2–3% at a threshold corresponding or close to maximal sprint speed.[23​] As the game has evolved, more recent data have indicated that high-intensity runs during match play have increased by ~30%,[39​] and that straight-line sprints are the most frequently demonstrated action of both scoring and assisting players in goal situations.[30​] The frequency and intensity of high-speed running is influenced by several factors including formation, playing position, age and playing level;[23​] however, sprint distances in elite male and female soccer players are typically less than 10 m.[40​] The potential for caffeine to improve lower limb power, inferred by improved vertical jump performance, may lead to speculation of a transfer effect to straight-line sprint speed. Whilst there is some evidence, typically administering 3 mg·kg⁻¹ caffeine, demonstrating small improvements in 20 and 30 m sprint time in both elite and sub-elite participants,[35] [36​] [41] [42] [43​] fewer studies have considered effects on ≤10 m sprinting, and although there is some support,[43​] there is also evidence for a lack of an effect,[42​] even when doses of up to 5 mg·kg⁻¹ are administered.[44​] It should also be considered that studies evaluating sprint ability typically assess performance from a standing start. Soccer performance also requires curved running and rapid CoD. Furthermore, the evidence discussed thus far is specific to a single bout of running and elite soccer players on average will perform 11 sprint efforts per game.[45​] Therefore, it is important to consider the effects of caffeine on repeated sprint running performance.

There is support from meta-analyses regarding the beneficial effects on anaerobic power;[9​] however, studies that have specifically considered repeated sprint performance are equivocal which is likely attributable to differences in work:rest ratios and exercise modalities (sprint running vs. cycling).[46​] When sprint running specifically is considered, there is some evidence to support small improvements in repeated sprint performance;[47] [48] [49] [50​] however, benefits have been shown to be prevalent for some sprint efforts and not all, sprint distances are ≥ 20 m, rest durations vary (30–60 s in the cited studies), and studies typically consider effects of higher doses of caffeine 5–6 mg·kg⁻¹. Whilst there may be effects at lower doses (e.g., 200 mg), these effects may be specific to low habitual consumers.[51​] Furthermore, beyond a lack of consistency in published findings, there is a need for caution regarding the direct translation of these results to soccer given the lack of studies that consider soccer-specific work:rest ratios and that sprint running is interspersed with varied intensity of submaximal running and walking. As outlined, across the course of a 90+ minute match, players on average will perform 11 sprints [45​] where evidence in female soccer players has demonstrated a time of ~87 s between sprint bouts (>19 km/h), resulting in a work:rest of ~1:43.[40​]

Numerous studies have considered the ergogenic potential of caffeine on CoD performance. In comparison to repeated sprint running, positive outcomes are much more consistently reported and are prevalent across 1–6 mg·kg⁻¹ doses.[36] [52] [53] [54​] Effects have been demonstrated across several CoD​​​​​​ tests (e.g., arrowhead agility, 5-0-5, Illinois agility run), many of which are used for soccer athlete profiling. Performance-enhancing effects have also been shown to occur in what might be considered more ecologically valid reactive CoD tasks [46​] and in team sports athletes in both fresh and fatigued states.[55​]

Caffeine may evoke more pronounced effects for endurance activity,[56​] where aerobic performance is an important discriminator between elite and sub-elite soccer players.[57​] Whilst the effects of caffeine on aerobic function have been determined across several exercise modalities consisting of time trial and fixed duration activity,[1] [2] [3] [4​] it is important in the context of this review to consider assessment methods that best represent the physiological demands of soccer, which is dependent on both aerobic and anaerobic energy contribution. One assessment that has been particularly advocated in this regard,[58​] and has received attention in the literature examining the ergogenic potential of caffeine, is the Yo–Yo intermittent shuttle run (Yo–Yo IR). Several studies support improved performance in variants of the Yo–Yo IR, where evidence is much less equivocal than other modes of exercise and there appears to be little benefit of higher doses (6 mg·kg⁻¹) over lower doses (200 mg absolute dose).[59​] Further to this in professional and semi-professional players, 6 mg·kg⁻¹ caffeine has been shown to increase time to exhaustion running performance at 70% VO_2max, following the completion of three 22.5 minute bouts of a treadmill running protocol designed to replicate the physiological demands of soccer.[60​] Such effects were prevalent independent of cardiorespiratory or neuromuscular fitness level.

Whilst it might appear caffeine may produce favourable effects on the outlined physical performance facets, when studies evaluate multiple assessments in the same study, it is rare to see beneficial effects in all measured outcomes.[34] [61] [62​] However, it should be noted that the interpretation of the results from studies focusing on multiple outcomes is somewhat limited by the small sample sizes and intraindividual variation in performance measures.[63​] Furthermore, for each of the listed assessments, contradictory results can be found,[61] [62] [64] [65] [66​] which have been attributed to several potential moderators of caffeine’s effects. Specifically, dose, habituation, time of day, athletic level and difference in gene polymorphisms responsible for caffeine metabolism and sensitivity may influence effects.[67​] These potentially interacting moderators likely explain interindividual caffeine responses and infer that an individualised supplementation strategy is needed to maximise effects.

Effects of caffeine on soccer-specific cognitive functions

Soccer has a substantial cognitive demand where players are required to maintain high levels of attention and make rapid decisions in a dynamic environment.[68​] As such, soccer has been suggested to elicit cognitive fatigue,[68​] where in such circumstances caffeine may offer superior effects.[69​] Executive functions represent an important cognitive function subgroup within this context and can be divided into core (working memory, cognitive flexibility and inhibitory control) and high-level (reasoning, problem solving, and planning) executive functions.[70​] Effective executive functions are particularly relevant given their association with technical proficiency.[71​]

Caffeine has been shown to elicit beneficial effects on self-report energy and mood as well as low-order cognitive functions such as attention, vigilance, reaction time and memory which may be beneficial for improved soccer performance.[10] [72​] Positive effects have been shown at doses as low as 1 mg kg⁻¹,[72​] and caffeine’s effect on cognition may be specific to lower doses. For example, Zhang et al.[73​] demonstrated that only 3 mg kg⁻¹ caffeine was effective in improving both reaction time and brain activation compared to higher doses (6 or 9 mg kg⁻¹). Where increased anxiety and tension that may occur because of higher dose supplementation may result in attentional narrowing, and as a result, less effective information processing.[72​]

Whilst it might seem intuitive that such effects may translate to soccer performance, studies specific to the cognitive demands of soccer are limited and results are inconclusive. Jafari et al. [74​] demonstrated that 3 mg kg⁻¹ caffeine impaired decision-making in a computerised task where participants were challenged in evaluating the most appropriate outcome in simulated pre-recorded soccer events. Similarly, whilst small-sided games have been shown to improve response time in the Stroop test, in a sample of professional male soccer players, 5 mg kg⁻¹ caffeine reduced both post-exercise reaction time and accuracy.[75​] Field et al. [76​] demonstrated that 200 mg caffeinated chewing gum administered 90 min following soccer-specific exercise attenuated the declines in reaction time but reduced composure when assessed during the extra-time period of simulated soccer match play using a soccer-specific virtual reality simulator.[76​]

One key aspect for future studies wishing to determine the impact of caffeine on cognitive performance specific to soccer is in the use of ecologically valid assessments alongside representative research designs. While there is some evidence that caffeine may modulate cognitive responses in some cognitive functions related to soccer performance, the research designs employed to date are limited, with a tendency to examine cognition pre-post some form of soccer perfor.ance (e.g., ref. [75​]), or in simulated match play (e.g.,ref. [77​]). Likewise, in studies that have employed a technical motor skill task (e.g.,ref. [74​]), this does not really effectively assess soccer-specific cognition. There are emerging research designs that could be employed in future work which better explore applied aspects of cognition in a soccer-specific manner such as work assessing soccer-specific divergent thinking and creativity, determined via performance analysis in game play.[78​] To date such designs have not been considered in the context of caffeine ingestion, or other nutritional ergogenic aids, but for progress in relation to caffeine’s effects on soccer performance, such representative designs and assessments are needed.

Effects of caffeine on technical, tactical performance and match play

Technical proficiency is an important determinant of success and relies on the interaction of motor control, perception and cognitive functioning.[79​] However, studies examining the effect of caffeine on technical skill performance are lacking. Current work appears specific to passing performance where 3 mg·kg⁻¹ has been demonstrated to improve both short and long passing accuracy, but in the same study, reduced performance in the more demanding Loughborough soccer passing test (LSPT).[74​] Conversely, Foskett et al. [77​] demonstrated improved LSPT performance following 6 mg·kg⁻¹ ingestion when assessed several times across 90 minutes of the Loughborough Intermittent Shuttle Test. Mor et al. [53​] further demonstrated no effect of caffeine on ball kicking speed, but this was measured independent of accuracy. With respect to understanding the effects of caffeine on technical proficiency, researchers should carefully evaluate the between-session reliability of the chosen assessments as some of the cruder measures of performance (e.g., distance of the ball from a target in a passing task over a relatively small number of attempts) may lack the sensitivity to accurately detect what are typically small effects. This idea has been discussed in a recent publication by our group.[63​]

A more representative examination of the effects of caffeine on soccer-specific performance might be to elucidate the ergogenic potential during match play. A small number of studies have taken this approach and there is some support for an increase in total distance covered, high-speed running distance covered, and number of sprints, in both male and female athletes following 3 mg·kg⁻¹ consumption.[35] [80​] Similar outcomes have been demonstrated in other sports.[81​] Interestingly, Pettersen et al. [82​] demonstrated no effect using a similar approach in elite adolescent athletes following 6 mg·kg⁻¹ caffeine. Whilst such studies have been valuable to enhancing the understanding of the performance-enhancing potential of caffeine for soccer match play, they should be approached with caution given that the physical demands of match play are heavily influenced by opponents, environmental conditions and tactics, factors that are difficult to control.

The effect of caffeine on tactical performance has been scarcely considered. Recent work by de Almeida et al. [83​] demonstrated that acute caffeine ingestion resulted in a reduction of defensive errors and an increase in ball possession during a repeated small-sided games protocol with professional soccer players. However, the impact of caffeine on tactical performance was heterogeneous, with some positive effects on offensive decision-making but a decrease in total defensive success in specific scenarios. This highlights the complexity of tactical analysis, which involves various outcomes (i.e., distinct offensive and defensive actions). Although speculative, one hypothesis is that different levels of arousal might be required for different tactical actions during the game, and the effects of caffeine may vary according to this relationship. This is an area of interest for future studies. Although, as previously indicated, caution is needed in the interpretation of these results given that the improved ecological validity of such study design results in impaired experimental control, which in the case of the current work could be improved by more rigorous consideration of the between-session reliability of the outcome measures. In conclusion, research evaluating the effect of caffeine on soccer on technical, tactical performance and match play is sparse, and whilst caffeine may benefit gross physical function, effects on tactical and technical outcomes range from negative to positive. However, it is difficult to exert full confidence in these findings.

Knowledge gaps and limitations to practice

Several areas of future work are needed to provide more robust evidence-based guidance for optimised caffeine use in soccer. In fact, a translational gap between science and practice specific to the use of caffeine supplementation in soccer has been previously highlighted.[11​] Priorities for caffeine-focused research for sport and exercise science applications have been the subject of extensive recent reviews,[67] [84​] and whilst several of the points identified are relevant, here we will provide a brief account of priorities specific to caffeine use in soccer.

1. Ecologically Valid Tests: As outlined throughout this review, understanding the potential efficacy of caffeine as a performance-enhancing supplement is somewhat limited by the lack of ecologically valid assessments. Regarding isolated assessment of the physical components important for performance, specific focus is needed on replicating the sprinting and repeated sprint demands of match play. Similarly, while there is evidence supporting the beneficial effects on cognitive performance, the application of isolated assessments of cognitive functions to match play remains somewhat limited. Consequently, there is a clear need for future research to explore the interaction of football-specific cognitive functions within scenarios that more closely reflect actual match play. This approach should also consider cognitive fatigue and multitasking processes, including their synergistic interaction with physical demands. Furthermore, work is needed to better understand caffeine effects on tactical and technical performance using assessments where the between-session reliability of the outcomes is established, as well as consideration of position-specific demands, where in particular goalkeepers are poorly represented. These considerations should extend to evaluation of the impact of both mood as well as physical and cognitive fatigue, which influence caffeine erogenicity.[63​] In general, the translation of research findings to enhanced performance is limited by study designs representative of the demands of soccer, and future work should be considered with this in mind.

2. Genetic Variation: Polymorphism in genes responsible for caffeine metabolism (Cytochrome P450 1A2 [CYP1A2]) and the adenosine A2A receptor (ADORA2A) have been highlighted as potential moderators to caffeine’s ergogenic effects and may explain interindividual responses.[67​] Whilst there is some supporting evidence that carriers of the TT allele of ADORA2A [85​] and the AA allele of CYP1A2 may result in superior effects,[86​] there is an equal number of studies that indicate no influence of these gene polymorphisms.[87] [88​] There is some suggestion that genotype effects may be specific to exercise modalities and influenced by dose.[87] [88​] Furthermore, slow caffeine metabolisers may in fact initially see a reduction in performance, and an improvement that takes longer than the 45–60-minute ingestion period typically used in previous work.[89​] The effect of gene polymorphisms that may influence caffeine’s erogenicity is yet to be considered in a soccer-specific context. One way to address this would be to stratify individuals into groups based on multiple potentially influential genetic polymorphisms and then compare the ergogenic potential of caffeine on measures of match-play performance between these groups. However, this approach presents significant logistical and financial challenges, given the large number of participants required to conduct a study of this design.

3. Effects For Female Athletes: The wealth of evidence examining the ergogenic effects of caffeine is weighted towards male participants and there is a need to extend this understanding to female athletes. Oral contraception can increase the time for caffeine clearance,[90​] and differences in body composition and hormonal function have provided a theoretical basis for sex-specific effects.[91​] However, recent meta-analyses specific to female athletes demonstrate improved muscular strength, strength endurance and vertical jump performance following acute caffeine ingestion.[37] [92​] Interestingly, the caffeine-induced increase in vertical jump performance was prevalent across different menstrual phase cycles but was greatest in the follicular phase.[37​] A meta-analysis summarising the small number of studies that have directly compared the sex-specific effects of acute caffeine consumption indicates a similar level of benefit for aerobic-based activity; however a greater effect for males completing anaerobic activity.[91​] This ambiguity in published findings and lack of studies specific to soccer highlight a need for further investigation.

4. Time Course Effects & Repeated Dosing: Repeated dosing appears to be common practice in professional soccer;[11​] however, studies examining the time course of caffeine-induced effects and the value of repeat dosing are lacking.[67​] Five mg kg⁻¹ caffeine has been shown to improve endurance cycling performance when consumed 6 h prior to exercise; however, in habitual caffeine users, effects were only prevalent 1 and 3 h prior to exercise.[93​] Furthermore, a divided caffeine dose consumed prior to and during endurance cycling elicited a similar benefit to a bolus dose administered prior to task completion.[94​] However, such effects may be influenced by exercise modality. In a simulated wrestling tournament consisting of five matches over 6 h, 10 mg kg⁻¹ improved performance in the first bout, and a 2 mg kg⁻¹ divided dose elicited beneficial effects in both the third and fourth matches. An individual dose based on performance decrement elicited the longest time course of effects improving performance in matches three to five.[95​] The current lack of research specific to the time course effects of caffeine for soccer performance somewhat limit recommendations regarding the effectiveness of repeated dosing and is an important area for future investigation.

Recommendations for athletes & practitioners

Despite a need for future work, the presented review of the literature indicates the potential for a small but significant caffeine-induced improvement in several facets important to soccer performance. However, there remain challenges in realising and maximising this potential. Guided by the available evidence, advice for athletes and practitioners is presented and summarised in [Fig. 1].

Fig. 1 A guide to caffeine supplementation in soccer: recommendations for athletes & practitioners.

1. Understand Caffeine Consumption Habits : Before administering caffeine for the purpose of improved performance, it is first important to monitor an athlete’s typical caffeine consumption habits. This information is essential for mitigating adverse effects, managing potential effects of habituation, and ensuring that the chosen supplementation strategy is not influenced by prior or post-caffeine intake. Whilst this is somewhat challenging given the varying caffeine doses in different batches of the same product,[96​] there is no standardised approach for determining caffeine consumption habits [97​] and several monitoring tools exist which lack commonality.[98​] However, from an application perspective, there is a need to balance rigour with timeliness, particularly in team-based sports such as soccer. Whilst weighted food records and food diaries offer greater accuracy,[99​] several caffeine-specific consumption surveys exist. Whilst some of these surveys focus on quantifying “typical” caffeine consumption,[100​] the Caffeine Consumption Questionnaire (CCQ) [100​] and the questionnaire and calculation programme developed by Bühler, Lachenmeier, Schlegel and Winkler [101​] are relatively simple and have been used readily in the scientific literature. Such surveys may be particularly useful in the context of soccer given that both capture caffeine consumed from a range of products and consider the time-specific nature of these habits across a day. Monitoring this over a 24-hour period is recommended to understand how consumption habits are influenced at specific points over a competitive week. It is recommended that such surveys are used in conjunction with databases such as Caffeine Informer (https://www.caffeineinformer.com/) to improve the accuracy of estimation. Whilst it is recommended to initially understand the interindividual reliability of caffeine consumption habits, such information may not need to become part of regular athlete monitoring but could be conducted periodically. This information should inform player education regarding the use of caffeine and form the basis of an individualised supplementation strategy.

2. Player & Coach Education: Player and coach education is important for safe and effective supplementation and should extend beyond advice regarding dose, timing and modality. This should be expanded to several further factors to provide holistic guidance regarding caffeine practices. Specifically, players should be educated on the effects of acute caffeine on facets important to soccer match play, how to manage caffeine consumption prior to and following caffeine prescribed to elicit improved performance, scenarios where consumption may evoke the greatest benefit, synergistic effects with other supplements, adverse effects and implications of misuse, and factors that might preclude safe consumption.

   Player education should be informed by knowledge of caffeine consumption habits and perception of its effects. Whilst evaluating athlete caffeine consumption provides important information about the quantity and frequency of caffeine use, it reveals little regarding motivation for consumption, expectation regarding performance-enhancing effects, and potential dependence or abuse. Such information is not only important for tailored education but also for guiding safe and effective practice. Moreover, several studies indicate that instilling positive caffeine expectancy may evoke improved cognition and physical performance in athletic assessments in a magnitude similar to that evoked as a result of the pharmacological effects induced by ingestion.[102​] As such, measuring and manipulating caffeine expectancy may represent and effective strategy to induce improved soccer match play. However, it should be noted that positive caffeine expectancy is influenced by previous caffeine experience, the quality of the education provided, and the method and credibility of the individual delivering the information.[103] [104] [105​] When instilling expectancy, care should be taken that this is not approached in a way that evokes risk and is in line with safe caffeine consumption practices.

   With this in mind, both the Motives for Caffeine Consumption Questionnaire (MCCQ) or Caffeine Expectancy Questionnaire (CaffEQ) may be appropriate. The MCCQ is a 34-item Likert scale survey that evaluates motivational factors related to alertness, habit, mood, social, taste and symptom management.[106​] However, some of the specific questions that make up these factors are specific to coffee consumption or do not well represent competitive sporting environments. Although not interchangeable in the constructs assessed, the CaffEQ may represent and appropriate alternative providing information regarding positive and negative valanced expectancies related to (a) withdrawal/dependence, (b) energy/work enhancement, (c) appetite suppression, (d) social/mood enhancement, (e) physical performance enhancement, (f) anxiety/negative physical effects, and (g) sleep disturbances.[107​] In a large sample of adults with varied caffeine consumption habits, the CaffEQ has been demonstrated to be valid for the seven psychometric properties assessed and to have good test-retest reliability. To overcome the time constraints of administering this survey, the 20-item Brief-CaffEQ (B-CaffEQ) could be used and has shown acceptable performance compared to the original 47-item scale [108​]

3. Supplementation For Match Play: An individualised caffeine supplementation strategy is advised based on the potential for an interindividual response, habitual caffeine consumption and caffeine expectancy. However, the available evidence would indicate a dose of ≤3 mg kg⁻¹ prior to match play might represent an appropriate balance between performance-enhancing effects across the different facets important for match play, whilst limiting potential adverse effects. Whilst doses lower than 3 mg kg⁻¹ may elicit some task-specific benefits, evidence supporting the ergogenic potential of low-dose caffeine across a broader range of physical performance facets remains limited. Conversely, evidence supporting the potential of 3 mg kg⁻¹ dose is more compelling.[67​] Although there is little support for a dose-response effect, higher doses might be needed to recognise performance improvements in some facets of physical function, in particular maximal strength,[8] [109] [110​] and in the function of upper body musculature.[111​] However, improved performance in measures of soccer-specific endurance performance, jump height, sprint speed, CoD performance, and high-speed running during match play has been demonstrated at a dose of 3 mg kg⁻¹.[4] [36] [59] [80​] Doses greater than this increase the risk of evoking adverse effects that may influence cognitive function and other aspects of performance.[112​] Furthermore, a dose of ≤3 mg kg⁻¹ may be more suited to balancing effects on both physical and cognitive function. As an example, Waer et al. [113​] demonstrated that low-dose caffeine (100 mg) improved simple reaction time but had no effect on the physical function of healthy middle-aged females. However, the reverse was true when a higher dose (400 mg) was consumed.

   It is recommended that caffeine be administered in anhydrous form; however, there is growing evidence supporting administration via caffeinated chewing gum, which has logistical benefits and results in a faster onset of effects due to more rapid absorption. The increased onset of effects has been attributed to absorption into the bloodstream via the highly vascularised buccal mucosa,[114​] and/or activation of bitter taste receptors [115​] and antagonistic effects on adenosine receptors in the oral cavity.[116​] Benefits to physical performance have been shown 15 minutes post-maceration,[117​] with caffeine in blood plasma peaking once at this time and again 50 minutes later as a result of absorption through the gut.[118​] Presently, there is little evidence to support caffeine administered via other modes, including the use of caffeine mouth rinsing,[119​] and therefore, this practice is not recommended.

   Caffeine anhydrous should ideally be administered in capsule form rather than dissolved in large volumes of liquid or carbonated drinks, to minimise the risk of gastrointestinal discomfort. Delivering caffeine anhydrous in capsule form also reduces the likelihood of dosing errors due to inaccuracies in weighing. Another way to mitigate this risk is to use commercially available, “off-the-shelf” caffeine-only tablets; however, careful attention must be paid to the absolute dose provided by each tablet. This consideration can also be extended to caffeinated chewing gum and energy drinks/shots. Given the potential risk of dosing errors with caffeine anhydrous, appropriate weighing and preparation methods should form an important part of player and coach education. Irrespective of method of consumption, where possible, it is advisable to use batch-tested products.

   Post-ingestion, caffeine in the blood plasma has typically been suggested to peak after ~60 minutes,[72​] although it may take as long as 80–120 minutes in some individuals.[120] [121​] It should be noted that peak plasma concentration is highly individual and at least in part is attributable to polymorphisms in genes that encode enzymes involved with caffeine digestion.[89​] Given the duration of match play and that caffeine effects are unlikely to be specific to the time of peak plasma concentration, ingestion of caffeine anhydrous 30 minutes prior to match play would mean that for most athletes, peak plasma concentration would occur prior to the final 45 minutes of the first half when athletes are likely to experience greater fatigue. However, it may be desirable to shift the ingestion time to coincide with tactics.

   Practitioners and athletes should be aware that caffeine has a half-life of 1.5–9.5 hours,[122​] and therefore repeat dosing in high concentrations, which appears to be prevalent in English professional soccer,[11​] is not advised. Given the suggestion in previous work that a divided dose may offer more sustained benefits,[95​] a suitable approach may be half time supplementation with a low dose (e.g., ~1 mg kg⁻¹) of caffeinated chewing gum, which may be suitable for maintaining caffeine blood plasma levels close to the peak for the remainder of the match. However, it should be noted that there is limited evidence to determine if peak blood plasma concentration corresponds with peak performance-enhancing effects and further work is needed to evaluate the suitability of this approach.

   It should also be noted that consumption of caffeine following a high carbohydrate meal has been shown to reduce the speed of digestion and prevalence in the blood plasma [123​] highlighting a need to consider caffeine supplementation strategy holistically within the wider nutritional programme.

4. Supplementation For Training: Adopting a similar caffeine consumption strategy to that recommended for match play may also be suitable to enhance training performance. However, the importance of improved performance in training should first be considered. Whilst it may be conceivable that a caffeine-induced increase in training intensity may result in improved adaptation if apparent across a training block, evidence examining the effect of chronic supplementation for this purpose in the most part demonstrates this not to be the case.[124] [125​] Although a point of contention, there is a long-standing paradigm that regular caffeine consumption may evoke habituation to its effects. However, this idea has been somewhat discredited based on the results of a recent meta-analysis,[126​] although conclusions are largely drawn from comparing studies evaluating acute effects in participants with different habitual caffeine consumption levels. Studies examining chronic caffeine supplementation (i.e., repeated doses in the same population) on athletic and cognitive function are limited, but there is some evidence to suggest a reduction, and in some cases, a blunted response.[127] [128​]

   Practitioners should also be mindful that caffeine may mask the time course of recovery assessed via objective evaluation of neuromuscular fatigue,[129​] as well as influence outcomes in physical performance profiling assessments. Data from a survey of professional soccer clubs in the top four English leagues indicates a high prevalence of caffeine use prior to training,[11​] where from a practitioner perspective there appears to be little advantage to administering caffeine to enhance training performance. However, given that performance in training may influence selection, caffeine supplementation may be perceived as desirable from an athlete’s perspective.

5. Monitor Adverse Effects: Athletes and practitioners should be aware of the impact of caffeine on sleep which may exacerbate detrimental effects on sleep quality that occur post-evening match play [130​] and as a result of international travel.[131​] In fact, insomnia was the most commonly reported side effect from caffeine supplementation in professional soccer.[11​] The effects of caffeine on sleep are well documented, with reduced total sleep time, increased time it takes to fall asleep, amount of time awake during the night, light sleep, and decreased deep sleep duration and proportion all reported.[132​] Specifically, recent evidence demonstrates that for moderate users, 400 mg can result in sleep disruption when consumed within 12 hours of bedtime, with adverse effects increasing closer to bedtime.[133​] However, such effects may not be prevalent when lower amounts (100 mg) are consumed.[133​] Importantly, reduced sleep has been shown to impair processes involved with exercise recovery, reduce mental wellbeing, as well as physical and cognitive functions.[134] [135] [136] [137​] Although caffeine has been shown to be effective in mitigating impaired physical and cognitive function as well as sport specific skill execution as a result of sleep deprivation,[138] [139​] the impact of caffeine on sleep should be monitored, particularly during intense periods of the season.

   It is also important to be aware of other side effects of caffeine that can occur relatively acutely and, in the days, following consumption. Side effects specific to caffeine consumption in professional and amateur athletes have been recently summarised, where in addition to insomnia, headaches, anxiety, irritability, and gastrointestinal problems have been shown to occur.[112​] The incidence of such effects is relatively low following exposure to doses ≤3 mg kg⁻¹ and increase with quantity consumed. As such, it is important to monitor adverse effects and adapt the supplementation strategy accordingly.

   There has also been recent interest in health effects associated with caffeine consumption. Evidence suggests that ≤400 mg/day in adults is not associated with overt, adverse effects,[140​] and within typical levels caffeine may evoke health benefits.[141​] That said caffeine supplementation should not be recommended for athletes with cardiovascular illness, unmedicated hypertension or isolated systolic hypertension, sleep or anxiety disorders, those prescribed certain medications, and individuals with low bone mineral density.[142] [143] [144] [145​] This is not an exhaustive list and should be considered based on appropriate health screening, and where relevant, advice sought from a medical professional. Although ≤2.5 mg kg⁻¹ per day in children and adolescents is suggested to not result in adverse health effects,[140​] caffeine supplementation is not recommended for these age groups.

6. Genetic Testing May Be Useful, but Evidence is Not Robust: Genetic testing is becoming more commercialised and easily accessible,[146​] with a specific market for elite sports clubs. A survey of UK elite athletes and sports staff indicates a willingness to engage in genetic testing to improve sports performance,[147​] an opinion shared by key stakeholders in professional soccer.[148​] Whilst genetic testing for ADORA2A, HTR2A and particularly CYP1A2 polymorphisms may offer some insight that may inform caffeine susceptibility and supplementation strategy, evidence is not conclusive and the influence on the integrating facets important to soccer match play has not yet been considered which currently preclude the cost/benefit of this analysis.

7. Time of Day Effects: Athletes and practitioners should also be aware that caffeine effects may be influenced by time of day. Across several facets of physical function, performance in the afternoon has been demonstrated to be superior to that in the morning. Caffeine may be most effective in alleviating the morning performance decline, with a number of studies indicating benefits of acute ingestion are reduced or not prevalent in the afternoon when compared to the morning.[42] [149] [150] [151​] Whilst the mechanism unpinning this has not been fully elucidated, this difference is unlikely attributable to time-of-day differences in plasma concentration which have been shown to be similar in the morning and afternoon.[149​] One explanation may be the action of Cytochrome P450 1A2, the enzyme responsible for caffeine metabolism, which has been suggested to have higher activity directly after waking compared to the rest of the day.[150​] However, it is important to note that these studies fail to consider the complex demands of soccer match play and interindividual responses. Given this evidence, it is advisable to determine the effectiveness of the selected dosing strategy for individuals at different times of the day, given the potential adverse effects of caffeine on sleep. Such work is particularly important given that soccer match kick-off times often range from midday to evening. As such, the potential benefits of caffeine supplementation may need to be evaluated on a game-by-game basis.

8. Co-ingestion With Other Ergogenic Aids : Research evaluating the synergistic effect of caffeine and co-ingestion with other ergogenic aids is sparse [67​] and available evidence fails to robustly support an additive response. Bicarbonate loading (extracellular buffer) is effective in inducing improved anaerobic performance,[152​] but in a recent review, only one (specific to judo performance) out of eight studies demonstrated and additive effect of co-ingestion with caffeine.[153​] There is also limited support for additive effects of co-ingestion with creatine [154​] and nitrate/beetroot juice.[155​] In fact, caffeine ingested with bicarbonate or creatine may increase gastrointestinal discomfort [156] [157​] which may impair performance, and in the case of creatine, caffeine may hinder the loading phase.[158​] There is evidence to suggest that co-ingestion of caffeine in combination with a 6–9% of carbohydrate solution may incur synergistic performance benefits or attenuate the effects of fatigue,[159] [160] [161] [162​] however, the application to soccer is yet to be elucidated. Collectively, the evidence indicates that the combination of performance-enhancing supplements needs to be carefully considered and should be advised and administered by professionals.

Conflict of Interest

The authors declare that they have no conflict of interest.

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Publication History

Received: 10 March 2025

Accepted after revision: 24 September 2025

Accepted Manuscript online:
24 September 2025

Article published online:
24 November 2025