Caffeine for Endurance
Caffeine taken before exercise produces a small but consistent improvement in endurance performance, with the benefit growing for longer-duration events. It works, but the gains are modest rather than dramatic.
Why this grade7-layer evidence engine
This earns a Preliminary (B) grade because the efficacy signal is consistent across multiple high-quality meta-analyses, yet the effect size is small-to-moderate rather than large. A 2018 review of 46 studies (PMID 29876876) found caffeine raised mean power output by about 3% and shaved roughly 2% off time-trial times, while a 2019 analysis of 40 studies (PMID 30170953) reported a pooled benefit (Cohen's d 0.33) that grew with event duration.
Running-specific evidence agrees: a 2022 meta-analysis (PMID 36615805) showed improved time to exhaustion and faster time-trial performance versus placebo. The typical effective dose is roughly 3-6 mg per kg of body weight taken before activity. The grade is held at B rather than higher because effects are modest, individual response varies (partly tied to CYP1A2 genetics), and the pooled studies did not consistently disclose funding.
Regulators and clinics align but speak to different things. The FDA classifies caffeine as generally recognized as safe, and EFSA says single doses up to 200 mg before intense exercise pose no safety concern for healthy adults; both address safety and labeling, not an efficacy endorsement. Cleveland Clinic notes caffeine can increase endurance for high-intensity exercise while advising servings under 200 mg.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.661
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (3 篇 > 0 negative)
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status