Caffeine is a widely utilized performance-enhancing supplement used by athletes and non-athletes alike. In recent years, a number of meta-analyses have demonstrated that caffeine’s ergogenic effects on exercise performance are well-established and well-replicated, appearing consistent across a broad range of exercise modalities. As such, it is clear that caffeine is an ergogenic aid—but can we further explore the context of this ergogenic aid in order to better inform practice? We propose that future research should aim to better understand the nuances of caffeine use within sport and exercise. Here, we propose a number of areas for exploration within future caffeine research. These include an understanding of the effects of training status, habitual caffeine use, time of day, age, and sex on caffeine ergogenicity, as well as further insight into the modifying effects of genotype. We also propose that a better understanding of the wider, non-direct effects of caffeine on exercise, such as how it modifies sleep, anxiety, and post-exercise recovery, will ensure athletes can maximize the performance benefits of caffeine supplementation during both training and competition. Whilst not exhaustive, we hope that the questions provided within this manuscript will prompt researchers to explore areas with the potential to have a large impact on caffeine use in the future.

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Caffeine and Exercise: What Next?

Background In this Position Statement, the International Society of Sports Nutrition (ISSN) provides an objective and critical review of the literature pertinent to nutritional considerations for training and racing in single-stage ultra-marathon. Recommendations for Training. i) Ultra-marathon runners should aim to meet the caloric demands of training by following an individualized and periodized strategy, comprising a varied, food-first approach; ii) Athletes should plan and implement their nutrition strategy with sufficient time to permit adaptations that enhance fat oxidative capacity; iii) The evidence overwhelmingly supports the inclusion of a moderate-to-high carbohydrate diet (i.e., ~ 60% of energy intake, 5–8 g·kg− 1·d− 1) to mitigate the negative effects of chronic, training-induced glycogen depletion; iv) Limiting carbohydrate intake before selected low-intensity sessions, and/or moderating daily carbohydrate intake, may enhance mitochondrial function and fat oxidative capacity. Nevertheless, this approach may compromise performance during high-intensity efforts; v) Protein intakes of ~ 1.6 g·kg− 1·d− 1 are necessary to maintain lean mass and support recovery from training, but amounts up to 2.5 g.kg− 1·d− 1 may be warranted during demanding training when calorie requirements are greater; Recommendations for Racing. vi) To attenuate caloric deficits, runners should aim to consume 150–400 Kcal·h− 1 (carbohydrate, 30–50 g·h− 1; protein, 5–10 g·h− 1) from a variety of calorie-dense foods. Consideration must be given to food palatability, individual tolerance, and the increased preference for savory foods in longer races; vii) Fluid volumes of 450–750 mL·h− 1 (~ 150–250 mL every 20 min) are recommended during racing. To minimize the likelihood of hyponatraemia, electrolytes (mainly sodium) may be needed in concentrations greater than that provided by most commercial products (i.e., > 575 mg·L− 1 sodium). Fluid and electrolyte requirements will be elevated when running in hot and/or humid conditions; viii) Evidence supports progressive gut-training and/or low-FODMAP diets (fermentable oligosaccharide, disaccharide, monosaccharide and polyol) to alleviate symptoms of gastrointestinal distress during racing; ix) The evidence in support of ketogenic diets and/or ketone esters to improve ultra-marathon performance is lacking, with further research warranted; x) Evidence supports the strategic use of caffeine to sustain performance in the latter stages of racing, particularly when sleep deprivation may compromise athlete safety.

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International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing

Most studies that have shown the positive effects of caffeine supplementation on sports performance have been carried out on men. However, the differences between sexes are evident in terms of body size, body composition, and hormonal functioning, which might cause different outcomes on performance for the same dosage of caffeine intake in men vs. women. The main aim of this systematic review was to analyze and compare the effects of caffeine intake between men and women on sports performance to provide a source of knowledge to sports practitioners and coaches, especially for those working with women athletes, on the use of caffeine as an ergogenic aid. A structured search was carried out following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines in the Web of Science, Cochrane Library, and Scopus databases until 28 July 2019. The search included studies in which the effects of caffeine supplementation on athletic performance were compared between sexes and to an identical placebo situation (dose, duration and timing). No filters were applied for participants’ physical fitness level or age. A total of 254 articles were obtained in the initial search. When applying the inclusion and exclusion criteria, the final sample was 10 articles. The systematic review concluded that four investigations (100% of the number of investigations on this topic) had not found differences between sexes in terms of caffeine supplementation on aerobic performance and 3/3 (100%) on the fatigue index. However, four out of seven articles (57.1%) showed that the ergogenicity of caffeine for anaerobic performance was higher in men than women. In particular, it seems that men are able to produce more power, greater total weight lifted and more speed with the same dose of caffeine than women. In summary, caffeine supplementation produced a similar ergogenic benefit for aerobic performance and the fatigue index in men and women athletes. Nevertheless, the effects of caffeine to produce more power, total weight lifted and to improve sprint performance with respect to a placebo was higher in men than women athletes despite the same dose of caffeine being administered. Thus, the ergogenic effect of acute caffeine intake on anaerobic performance might be higher in men than in women.

https://www.mdpi.com/2072-6643/11/10/2313/pdf

Effect of Caffeine Supplementation on Sports Performance Based on Differences Between Sexes: A Systematic Review.

Caffeine is the most popular psychoactive substance in the world, and data suggests that it is widely used by athletes before competition to enhance physical and mental performance. The high number of athletes that regularly use caffeine suggests the need to investigate the effect of acute caffeine ingestion in athletes habituated to caffeine. However, most of the studies supporting this claim have used samples of athletes who do not consume caffeine on a regular basis, and with caffeine intake withdrawal prior to the experiments. A search through 19 databases conducted on habitual caffeine users was performed. The results of the studies regarding the ergogenic effect of caffeine in naive vs. habitual caffeine consumers are contradictory. The diversity of results are likely associated with the use of different thresholds to categorize individuals as naive or high caffeine consumers. There are no valid and standardized methods to accurately estimate the amount of caffeine ingested per day in athletes. We proposed a classification of athletes that habitually consume caffeine by using dietary questionnaires, and ultimately, to reduce the likelihood of discrepancies caused by the improper qualification of daily caffeine intake in studies directed at the assessment of acute caffeine intake in habitual caffeine consumers.

Inconsistency in the Ergogenic Effect of Caffeine in Athletes Who Regularly Consume Caffeine: Is It Due to the Disparity in the Criteria That Defines Habitual Caffeine Intake?

Background: The main goal of this study was to assess the acute effects of the intake of 9 and 11 mg/kg/ body mass (b.m.) of caffeine (CAF) on maximal strength and muscle endurance in athletes habituated to caffeine. Methods: The study included 16 healthy strength-trained male athletes (age = 24.2 ± 4.2 years, body mass = 79.5 ± 8.5 kg, body mass index (BMI) = 24.5 ± 1.9, bench press 1RM = 118.3 ± 14.5 kg). All participants were habitual caffeine consumers (4.9 ± 1.1 mg/kg/b.m., 411 ± 136 mg of caffeine per day). This study had a randomized, crossover, double-blind design, where each participant performed three experimental sessions after ingesting either a placebo (PLAC) or 9 mg/kg/b.m. (CAF-9) and 11 mg/kg/b.m. (CAF-11) of caffeine. In each experimental session, participants underwent a 1RM strength test and a muscle endurance test in the bench press exercise at 50% 1RM while power output and bar velocity were measured in each test. Results: A one-way repeated measures ANOVA revealed a significant difference between PLAC, CAF-9, and CAF-11 groups in peak velocity (PV) (p = 0.04). Post-hoc tests showed a significant decrease for PV (p = 0.04) in the CAF-11 compared to the PLAC group. No other changes were found in the 1RM or muscle endurance tests with the ingestion of caffeine. Conclusion: The results of the present study indicate that high acute doses of CAF (9 and 11 mg/kg/b.m.) did not improve muscle strength nor muscle endurance in athletes habituated to this substance.

https://www.mdpi.com/2072-6643/11/8/1912/pdf

The Effects of High Doses of Caffeine on Maximal Strength and Muscular Endurance in Athletes Habituated to Caffeine

Objective To systematically review, summarise and appraise findings of published meta-analyses that examined the effects of caffeine on exercise performance. Design Umbrella review. Data sources Twelve databases. Eligibility criteria for selecting studies Meta-analyses that examined the effects of caffeine ingestion on exercise performance. Results Eleven reviews (with a total of 21 meta-analyses) were included, all being of moderate or high methodological quality (assessed using the Assessing the Methodological Quality of Systematic Reviews 2 checklist). In the meta-analyses, caffeine was ergogenic for aerobic endurance, muscle strength, muscle endurance, power, jumping performance and exercise speed. However, not all analyses provided a definite direction for the effect of caffeine when considering the 95% prediction interval. Using the Grading of Recommendations Assessment, Development and Evaluation criteria the quality of evidence was generally categorised as moderate (with some low to very low quality of evidence). Most individual studies included in the published meta-analyses were conducted among young men. Summary/conclusion Synthesis of the currently available meta-analyses suggest that caffeine ingestion improves exercise performance in a broad range of exercise tasks. Ergogenic effects of caffeine on muscle endurance, muscle strength, anaerobic power and aerobic endurance were substantiated by moderate quality of evidence coming from moderate-to-high quality systematic reviews. For other outcomes, we found moderate quality reviews that presented evidence of very low or low quality. It seems that the magnitude of the effect of caffeine is generally greater for aerobic as compared with anaerobic exercise. More primary studies should be conducted among women, middle-aged and older adults to improve the generalisability of these findings.

https://bjsm.bmj.com/content/bjsports/54/11/681.full.pdf

Wake up and smell the coffee: caffeine supplementation and exercise performance—an umbrella review of 21 published meta-analyses

Background
We aimed to perform an umbrella review of meta-analyses examining the effects of sodium bicarbonate supplementation on exercise performance.

Methods
We systematically searched for meta-analyses that examined the effects of sodium bicarbonate supplementation on exercise performance. The methodological quality of the included reviews was evaluated using the Assessing the Methodological Quality of Systematic Reviews 2 (AMSTAR 2) checklist. Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework for downgrading the certainty in evidence was used, which included assessments of risk of bias, inconsistency, indirectness, imprecision, and publication bias.

Results
Eight reviews of moderate and high methodological quality met inclusion criteria. Using the GRADE framework, evidence for the ergogenic effects of sodium bicarbonate supplementation on peak and mean power in the Wingate test and Yo-Yo test performance was classified as being of moderate quality. The evidence for these outcomes did not receive a point on the indirectness GRADE item, as “serious indirectness” was detected. Low-quality evidence was found for the ergogenic effect of sodium bicarbonate supplementation on endurance events lasting ∼45 s to 8 min, muscle endurance, and 2000-m rowing performance. Evidence for these outcomes was classified as low quality, given that risk of bias, indirectness, and publication bias were assessed as “unclear”, “serious”, and “strongly suspected”, respectively. The ergogenic effects ranged from trivial (pooled effect size: 0.09) to large (pooled effect size: 1.26). Still, for most outcomes, sodium bicarbonate elicited comparable ergogenic effects. For example, sodium bicarbonate produced similar effects on performance in endurance events lasting ∼45 s to 8 min, muscle endurance tests, and Yo-Yo test (pooled effect size range: 0.36 to 0.40). No significant differences between the effects of sodium bicarbonate and placebo were found for general mean power, muscle strength, and repeated-sprint ability.

Conclusion
Based on meta-analyses of moderate to high quality, it can be concluded that sodium bicarbonate supplementation acutely enhances peak anaerobic power, anaerobic capacity, performance in endurance events lasting ∼45 s to 8 min, muscle endurance, 2000-m rowing performance, and high-intensity intermittent running. More research is needed among women to improve the generalizability of findings.

Effects of sodium bicarbonate supplementation on exercise performance: an umbrella review

Caffeine has been used as a performance-enhancing aid by athletes for many years. The first known study to explore the effects of caffeine ingestion on exercise performance dates back to 1907.1 Until recently, however, findings on this topic remained equivocal, despite a large number of published studies over the last 30 to 40 years.2 There are many possible reasons for the discrepant results between these studies, but one likely issue could be a common use of relatively small samples. To reconcile the equivocal evidence on this topic and overcome the low statistical power of individual studies, researchers have started to use meta-analytical methods. Meta-analysis is a statistical method that allows pooling of results from studies that address a similar research question.3 

Given that meta-analytical …

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Infographic. Wake up and smell the coffee: caffeine supplementation and exercise performance

ABSTRACT The present meta-analysis examined the effects of resistance training on increasing the rate of force development (RFD), followed by exploring the changes in RFD occurring during training cessation. Five databases were searched to find eligible studies. Their methodological quality was evaluated using the Downs and Black checklist. The data were pooled in a random-effects meta-analysis. Seven studies with 11 training groups were included in the meta-analysis. All studies were classified as being of good or moderate quality. Resistance training increased RFD (d: 0.24; 95% confidence interval [CI]: 0.09–0.38). There was no significant difference in RFD between the postintervention and postdetraining periods (d: −0.02; 95% CI: −0.10–0.06). In subgroup meta-analyses, there was no significant difference (all p > 0.05) between the postintervention and postdetraining RFD when categorized according to detraining duration (up to 4 weeks versus 7–16 weeks) or participants' training status (untrained versus trained). This meta-analysis demonstrated that resistance training effectively increases RFD. More importantly, the results also indicated that gains in RFD are maintained after detraining. Thus, unlike a few other resistance training–induced adaptations (e.g., increases in muscular strength and muscular endurance), it seems that gains in RFD are preserved during a detraining phase.

Resistance Training–Induced Gains in Rate of Force Development Are Maintained During Training Cessation: A Meta-Analysis

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Ivana Grgic

Papers

Wake up and smell the coffee: caffeine supplementation and exercise performance—an umbrella review of 21 published meta-analyses

Effects of sodium bicarbonate supplementation on exercise performance: an umbrella review

Infographic. Wake up and smell the coffee: caffeine supplementation and exercise performance

Resistance Training–Induced Gains in Rate of Force Development Are Maintained During Training Cessation: A Meta-Analysis

Acute coronary syndrome and cancer