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.
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.
well supported · human dataMeta-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.
Across 13 randomised placebo-controlled trials in rugby players, acute caffeine produced small improvements in sprint performance and lower perceived exertion, plus a large but highly heterogeneous effect on passing accuracy. Jumping, strength, metabolic and hormonal markers showed no significant change.
well supported · human dataSystematic review and meta-analysis of 15 studies (13 in the pooled analysis) in rugby players, but GRADE certainty was low to very low, and the passing-accuracy result showed high heterogeneity and possible small-study effects.
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.
well supported · human dataAcross 19 randomised trials with 732 participants using caffeine doses of 2 to 9 mg/kg, performance benefits were most consistent in people carrying the CYP1A2 AA genotype, smaller in AC carriers, and null or even detrimental in those with the CC genotype, though the studies did not all agree.
preliminary · human dataSystematic review of 19 RCTs in 732 athletes and physically active people published 2012-2024, with no meta-analysis and no consensus between studies; 84% of the included trials were rated as raising 'some concerns' for risk of bias and only two were low risk.
In 30 obese men, taking 6 mg/kg caffeine an hour before each sprint interval session for eight weeks produced greater gains than sprint training alone in fat mass, lower-body strength, cardiorespiratory fitness and blood lipids. Both training groups improved; caffeine added to the effect.
preliminary · human dataSingle small RCT: 30 obese men split three ways (n=10 per group) over eight weeks, with only three sessions a week and no women; effect sizes were mostly small to moderate and need replication in larger and more diverse samples.
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.
preliminary · human dataOne 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.
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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.