What does the evidence actually say?

What we hold on caffeine, endurance and performance

Read as:caffeineenduranceperformance

9 vetted claims match all three terms. Strongest evidence first.

1. Supplementswell supported · human data

   Pooled results from seven crossover trials in 103 people found acute caffeine gave a small boost to overall CrossFit performance (Hedges' g 0.13) and raised blood lactate; neither the relative dose nor training status significantly changed the effect.

   What it shows: A real but small edge: results pooled from seven small crossover trials covering 103 people, only 13 of them women. That thin, mostly male evidence base means the true size of the benefit could still shift.Meta-analysis · Nutrients

   Full breakdown →Caffeine guide →Caffeine Half-Life Calculator →

   Source: Effects of Acute Caffeine Supplementation on Performance and Physiological Responses in CrossFit: A Systematic Review and Three-Level Meta-Analysis. Nutrients 2026
2. Supplementswell supported · human data

   A systematic review of 23 studies found beetroot juice can improve cardiorespiratory endurance in athletes, increasing efficiency and time to exhaustion at submaximal intensities, though combining it with other supplements such as caffeine may undermine the effect.

   What it shows: Fairly persuasive but not settled: a sweep of 23 studies in athletes mostly pointed the same way, though the authors note some findings contradict each other. No numbers were pooled, so the size of the benefit is unclear.Systematic review · Nutrients

   Full breakdown →Caffeine guide →VO2max Calculator →

   Source: Effects of Beetroot Juice Supplementation on Cardiorespiratory Endurance in Athletes. A Systematic Review. Nutrients 2017
3. Supplementswell supported · human data

   Across 24 blinded crossover studies of real or simulated competition, acute caffeine intake increased high-intensity actions in intermittent sports such as team, racket and combat sports, including more sprints, accelerations, decelerations and body impacts. Caffeine also raised the success rate of sport-specific actions.

   What it shows: Strong for a supplement claim: results pooled from 24 trials where athletes took caffeine or a dummy in random order without knowing which, during real or simulated matches. The effects are modest rather than dramatic, and they will vary between sports and individuals.Meta-analysis · Int J Sports Physiol Perform

   Full breakdown →Caffeine guide →Caffeine Half-Life Calculator →

   Source: Can Caffeine Change the Game? Effects of Acute Caffeine Intake on Specific Performance in Intermittent Sports During Competition: A Systematic Review and Meta-Analysis. Int J Sports Physiol Perform 2024
4. Supplementswell supported · human data

   Pooling 48 randomised placebo-controlled trials (689 healthy adults), low caffeine doses of ≤3 mg·kg-1 shortened aerobic time-trial completion time (SMD -0.27), while moderate doses of 4-6 mg·kg-1 produced a larger and more consistent effect (SMD -0.52). No eligible trial reporting time-to-completion tested doses above 6 mg·kg-1.

   What it shows: Meta-analysis of 48 randomised placebo-controlled trials in healthy adults aged 18-59 using acute oral anhydrous caffeine, but only 689 participants in total, effects pooled as standardised mean differences across varied time-trial protocols, and no trials of doses above 6 mg·kg-1 met the inclusion criteria, so the top of the dose range remains untested for this outcome.Meta-analysis · Nutrients

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   Source: Dose-Response Effect of Oral Caffeine Use on Aerobic Exercise Performance: A Systematic Review and Meta-Analysis. Nutrients 2026
5. Supplementswell supported · human data

   Caffeine is one of the few supplements with strong, consistent evidence for performance, especially endurance, with useful effects on alertness and perceived effort; the ISSN position stand rates it clearly ergogenic.

   Caffeine guide →Caffeine Half-Life Calculator →

   Source: Guest NS, et al. ISSN position stand: caffeine and exercise performance. J Int Soc Sports Nutr 2021;18:1
6. Supplementspreliminary · human data

   A systematic review of endurance exercise in older adults found caffeine, and protein combined with beta-alanine, showed performance benefits in both sexes. Sodium bicarbonate and HMB looked favourable in older women, while older men saw no benefit from sodium bicarbonate or ubiquinone.

   What it shows: Early signals only: a sweep of all the studies on this turned up just 8 trials in older adults, too few and too varied to pool into a single estimate, so the sex differences here are hints rather than firm conclusions. The authors themselves say supplement use should be matched to the individual.Systematic review · Int J Environ Res Public Health

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   Source: Effect of Supplements on Endurance Exercise in the Older Population: Systematic Review. Int J Environ Res Public Health 2020
7. Supplementspreliminary · human data

   Pooled results from 24 studies in women show caffeine before resistance exercise slightly improves maximal strength and may boost muscular endurance in some protocols, but the certainty of evidence is low or very low and results vary widely.

   What it shows: Treat it as a starting point: a sweep of 24 studies in women found small average benefits, but the reviewers rate their own certainty as low or very low. Results swung so much between protocols that no dose, timing or population advice can be drawn from it.Systematic review · Front Physiol

   Full breakdown →Caffeine guide →Caffeine Half-Life Calculator →

   Source: Acute caffeine supplementation and resistance exercise performance in female participants: a systematic review and three-level meta-analysis. Front Physiol 2026
8. Supplementspreliminary · human data

   Endurance-trained men who took a ketone monoester with caffeine before 90 minutes of loaded treadmill work in 34 °C heat lasted longer in a subsequent time-to-exhaustion test than on carbohydrate, and scored better on the easier working-memory task. Harder cognitive tests, heart rate and core temperature were unchanged.

   What it shows: One randomised double-blind crossover trial in 17 endurance-trained young men with high VO2max; benefits appeared on some cognitive measures but not others, and the time-to-exhaustion difference was under two minutes on a short high-intensity test.RCT · J Int Soc Sports Nutr

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   Source: Ketone monoester ingestion and cognitive and physical performance during exercise-heat stress. J Int Soc Sports Nutr 2026
9. Supplementspreliminary · human data

   Despite appearing in energy drinks, taurine is a non-stimulant amino acid — any kick from the drink is the caffeine and sugar — and its own performance data is modest and inconsistent, a reasonable 'might help a little' rather than a reliable ergogenic.

   Taurine guide →

   Source: PubMed: taurine supplementation and exercise performance / recovery (trials and reviews)

Related, not an answer to your question

1. Supplementswell supported · human data

   Pooling 76 trials in healthy adults, dietary nitrate supplementation gave a small to moderate boost in time-to-exhaustion tests but made no significant difference to time-trial performance.

   What it shows: Strong for one narrow claim: results pooled from 76 trials in healthy adults showed a benefit only in tests of how long you can keep going, not in race-style time trials. Optimal dosing and who benefits most are still unknown.Meta-analysis · Sports Med

   Full breakdown →Beetroot juice guide →Running Pace Calculator →

   Source: The Effect of Dietary Nitrate Supplementation on Endurance Exercise Performance in Healthy Adults: A Systematic Review and Meta-Analysis. Sports Med 2017

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