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Open WellbeingWhat the studies actually measured

Energy and exercise

Caffeineand Endurance Performance (Time to Exhaustion)

Only one source here so far, and it measured higher endurance Performance (Time to Exhaustion).

How sure anyone can be

Moderate certainty, level 3 of 4

Further research may change this.

The numbers reported

One source’s range, drawn against its own line of no difference and scaled to its own numbers.

0.2140.392 standardised effect size0.571

This range stays on one side of the no-difference line.

Bar the confidence interval — the range the true effect is likely to sit inNotch the number the source reportedLine where there would be no difference at all

One source, newest first

What we read is the published abstract, not the full paper, so a blank below may still be printed in the paper itself. A fixed rule worked this out from the source’s own fields. Nobody checked this rating by hand.

  • Systematic review, 2022 · 21 studies pooled · 254 participants

    Moderate certainty, level 3 of 4

    Effects of Caffeine Intake on Endurance Running Performance and Time to Exhaustion: A Systematic Review and Meta-Analysis.

    Nutrients. 2022;15(1). doi:10.3390/nu15010148. PMID:36615805.

    Number reported
    0.392 standardised effect size
    Which way it went
    Higher
    Likely range
    0.214 to 0.571
    Source’s own words
    standardised mean difference (Hedges' g) for time to exhaustion vs placebo
    Who was studied
    Adult
    Compared with
    placebo
    Amount taken
    3 to 9 mg/kg body mass
    For how long
    Not in the abstract
    Disagreement between studies
    Not in the abstract
    Kind of record
    Journal article
    How this rating was reachedstarts at High, one step down: imprecision
    1. Starts at High
    2. Imprecision brought it down to Moderate254 participants is below the 400-participant optimal information size floorReported in the abstract
    3. Ends at ModerateOne step down.
    Checked, nothing to step it down for
    risk of bias and indirectness
    Inconsistency
    No high disagreement reported between the 21 studies it pooled

    Imprecision stops at the first check that applies; others may apply too.

    AI review could not confirm it — an AI agent re-read this finding against the saved source and at least one check failed. The batch record names the check and quotes the sentence that caused the doubt. No person read it.

    Read the abstract on PubMed

What is still missing from these readings

  • For how long — Not in the abstract.

Something nobody wrote down is never a zero and never a guess.

Still to read for Caffeine

Ten of the 19 things on our list for Caffeine have no reading here yet:

  • Anxiety
  • Cognitive performance
  • Estimated VO2max
  • Fatigue
  • Heart rate variability (RMSSD)
  • Light sleep
  • Number of awakenings
  • Resting heart rate
  • Serum cortisol (morning)
  • Wake after sleep onset (WASO)

Still to read means nobody here has got to it, not that it was tried and did nothing or that no research exists. A pairing on no list is not a gap: we never set out to read it.

Read next

This is a library, not advice. No recommendation, no dose, no diagnosis, no ranking. We never ask about your symptoms, and nothing here is tailored to you.