Does caffeine improve training performance?
What the studies we have published say — strongest evidence first. Every claim below links to the paper it came from.
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.
well supported · human dataFairly 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.
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.
well supported · human dataA 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.
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.
well supported · human dataStrong 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.
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.
preliminary · human dataEarly 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.
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.
preliminary · human dataTreat 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.
Across 26 randomised, placebo-controlled crossover trials, an acute dose of caffeine gave female team-sport athletes small improvements in repeated sprints, agility, sprint speed, anaerobic power and jumping, and modestly reduced how hard exercise felt. Evidence for sport-specific skills and cognition remained too thin to call.
well supported · human dataFairly solid for a small effect: results pooled from 26 trials where each athlete tried both caffeine and a dummy dose in random order. Effects on skills and thinking rest on too few studies to trust, and the data cannot yet say anything about the best dose or timing.
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This page collects what our published, cited studies say; it is information, not medical advice. Have a different question? Ask it here.