A new systematic review shows for the first time that low-dose caffeine (≤3 mg/kg) significantly shortens aerobic time-trial completion time (SMD = –0.27; p = 0.001). Moderate doses of 4–6 mg/kg work nearly twice as strongly (SMD = –0.52). High doses (>6 mg/kg) bring no extra benefit — only more side effects.
Caffeine is one of the most-studied ergogenic supplements: dozens of RCTs, varied doses, contradictory outcomes. For years, sports science has defaulted to the “3–6 mg/kg, 60 minutes pre-exercise” formula, treating lower doses as too small to matter.
A Brazilian group (Martins, Lancha-Jr et al.) pooled 48 randomized placebo-controlled trials in which participants ingested anhydrous caffeine before a cycling, running, or rowing time-trial. The meta-analysis included 716 participants. Doses were grouped into three tiers:
The authors used random-effects models (due to substantial between-study heterogeneity) and assessed risk of bias with the Cochrane RoB tool.
Both low and moderate doses produced statistically significant improvements in time-trial performance vs. placebo. The high-dose tier showed no additional advantage beyond moderate dosing.
| Caffeine dose | Effect (SMD) | 95% CI | p-value | Interpretation |
|---|---|---|---|---|
| ≤3 mg/kg (low) | –0.27 | –0.44 to –0.11 | 0.001 | small, but reliable |
| 4–6 mg/kg (moderate) | –0.52 | –0.77 to –0.28 | <0.0001 | moderate, most consistent |
| >6 mg/kg (high) | no edge | — | — | no extra benefit |
SMD (standardized mean difference) measures effect size: 0.2 is considered small, 0.5 moderate, 0.8 large. The negative sign is good here: time-trial completion time goes down, meaning the athlete finishes faster.
In practical terms: earlier reviews found caffeine effects on time-trial outcomes ranging from –3% (faster) to +16% (slower). This meta-analysis explains that variability through dose: the moderate 4–6 mg/kg range is the sweet spot for the effect/risk trade-off.
If you run, cycle, swim, row, or do steady-state cardio, the data apply directly. For a 70 kg adult, the doses translate to:
Timing: 45–60 minutes before exercise for peak plasma concentration. Source can be coffee, tea, caffeine tablets, or caffeinated gum; anhydrous caffeine in powder or capsule form performed most predictably in the studies due to precise dosing.
⚠ This is a preprint. Preprints are scientific manuscripts shared by the authors before full peer review. The findings look robust (48 RCTs, clear methodology), but conclusions may be refined when published in a journal. Do not use preprints as the sole basis for medical decisions.
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