FitProven
Evidence Breakdown
Based on 3 studies
Evidence map
For & against, at a glance
Meta-Analysis
Pro
Grgic J et al. · 2020British Journal of Sports MedicineUmbrella review of 21 meta-analyses covering endurance, strength, power, and sport-specific performance. Caffeine was found to improve muscle strength (ES: 0.20), muscle endurance (ES: 0.28), aerobic endurance (ES: 0.22-0.45), and anaerobic power. The evidence was consistent across meta-analyses, establishing caffeine as one of the most well-supported ergogenic supplements.
0.85
Umbrella review of 21 meta-analyses covering endurance, strength, power, and sport-specific performance. Caffeine was found to improve muscle strength (ES: 0.20), muscle endurance (ES: 0.28), aerobic endurance (ES: 0.22-0.45), and anaerobic power. The evidence was consistent across meta-analyses, establishing caffeine as one of the most well-supported ergogenic supplements.
Design Meta-Analysis (1.0) × quality 0.85 = impact 0.85
View sourceMeta-Analysis
Pro
Southward K et al. · 2018Sports MedicineMeta-analysis of caffeine and endurance time-trial performance. The figures below are those of the **published Correction** (doi 10.1007/s40279-018-0967-4), which supersedes the original article and restates the analysis as 44 included studies (the original said 46). Caffeine produced a small but evident benefit at moderate doses (3–6 mg/kg): mean power output improved by 2.92 ± 2.18% (effect size 0.22 ± 0.15) and time-trial completion time by 2.26 ± 2.60% (effect size 0.28 ± 0.12) versus placebo. The paper reports these as means ± standard deviations, not as pooled 95% confidence intervals. The response is not uniform — two studies reported *slower* time trials on caffeine and five reported *lower* mean power output — so the average effect conceals genuine non-responders.
0.85
Meta-analysis of caffeine and endurance time-trial performance. The figures below are those of the **published Correction** (doi 10.1007/s40279-018-0967-4), which supersedes the original article and restates the analysis as 44 included studies (the original said 46). Caffeine produced a small but evident benefit at moderate doses (3–6 mg/kg): mean power output improved by 2.92 ± 2.18% (effect size 0.22 ± 0.15) and time-trial completion time by 2.26 ± 2.60% (effect size 0.28 ± 0.12) versus placebo. The paper reports these as means ± standard deviations, not as pooled 95% confidence intervals. The response is not uniform — two studies reported *slower* time trials on caffeine and five reported *lower* mean power output — so the average effect conceals genuine non-responders.
Design Meta-Analysis (1.0) × quality 0.85 = impact 0.85
View sourceMeta-Analysis
Pro
Grgic J et al. · 2018Journal of the International Society of Sports NutritionMeta-analysis of 10 studies (149 participants) on maximal muscle strength and 10 studies (145 participants) on muscle power. Caffeine produced a small but significant improvement in overall strength (SMD 0.20; 95% CI 0.03, 0.36; p = 0.023) and in power (SMD 0.17; 95% CI 0.00, 0.34; p = 0.047). The subgroup analysis is the part that matters and is easy to get wrong: caffeine significantly improved **upper-body** strength (SMD 0.21; 95% CI 0.02, 0.39; p = 0.026) but **did not significantly improve lower-body** strength (SMD 0.15; 95% CI −0.05, 0.34; p = 0.147) — the lower-body confidence interval crosses zero. Effects are small even where significant, and the samples are predominantly male.
0.65
Meta-analysis of 10 studies (149 participants) on maximal muscle strength and 10 studies (145 participants) on muscle power. Caffeine produced a small but significant improvement in overall strength (SMD 0.20; 95% CI 0.03, 0.36; p = 0.023) and in power (SMD 0.17; 95% CI 0.00, 0.34; p = 0.047). The subgroup analysis is the part that matters and is easy to get wrong: caffeine significantly improved **upper-body** strength (SMD 0.21; 95% CI 0.02, 0.39; p = 0.026) but **did not significantly improve lower-body** strength (SMD 0.15; 95% CI −0.05, 0.34; p = 0.147) — the lower-body confidence interval crosses zero. Effects are small even where significant, and the samples are predominantly male.
Design Meta-Analysis (1.0) × quality 0.65 = impact 0.65
View sourceMeta-Analysis
Pro
Grgic J et al. · 2020British Journal of Sports MedicineUmbrella review of 21 meta-analyses covering endurance, strength, power, and sport-specific performance. Caffeine was found to improve muscle strength (ES: 0.20), muscle endurance (ES: 0.28), aerobic endurance (ES: 0.22-0.45), and anaerobic power. The evidence was consistent across meta-analyses, establishing caffeine as one of the most well-supported ergogenic supplements.
0.85
Umbrella review of 21 meta-analyses covering endurance, strength, power, and sport-specific performance. Caffeine was found to improve muscle strength (ES: 0.20), muscle endurance (ES: 0.28), aerobic endurance (ES: 0.22-0.45), and anaerobic power. The evidence was consistent across meta-analyses, establishing caffeine as one of the most well-supported ergogenic supplements.
Design Meta-Analysis (1.0) × quality 0.85 = impact 0.85
View sourceMeta-Analysis
Pro
Southward K et al. · 2018Sports MedicineMeta-analysis of caffeine and endurance time-trial performance. The figures below are those of the **published Correction** (doi 10.1007/s40279-018-0967-4), which supersedes the original article and restates the analysis as 44 included studies (the original said 46). Caffeine produced a small but evident benefit at moderate doses (3–6 mg/kg): mean power output improved by 2.92 ± 2.18% (effect size 0.22 ± 0.15) and time-trial completion time by 2.26 ± 2.60% (effect size 0.28 ± 0.12) versus placebo. The paper reports these as means ± standard deviations, not as pooled 95% confidence intervals. The response is not uniform — two studies reported *slower* time trials on caffeine and five reported *lower* mean power output — so the average effect conceals genuine non-responders.
0.85
Meta-analysis of caffeine and endurance time-trial performance. The figures below are those of the **published Correction** (doi 10.1007/s40279-018-0967-4), which supersedes the original article and restates the analysis as 44 included studies (the original said 46). Caffeine produced a small but evident benefit at moderate doses (3–6 mg/kg): mean power output improved by 2.92 ± 2.18% (effect size 0.22 ± 0.15) and time-trial completion time by 2.26 ± 2.60% (effect size 0.28 ± 0.12) versus placebo. The paper reports these as means ± standard deviations, not as pooled 95% confidence intervals. The response is not uniform — two studies reported *slower* time trials on caffeine and five reported *lower* mean power output — so the average effect conceals genuine non-responders.
Design Meta-Analysis (1.0) × quality 0.85 = impact 0.85
View sourceMeta-Analysis
Pro
Grgic J et al. · 2018Journal of the International Society of Sports NutritionMeta-analysis of 10 studies (149 participants) on maximal muscle strength and 10 studies (145 participants) on muscle power. Caffeine produced a small but significant improvement in overall strength (SMD 0.20; 95% CI 0.03, 0.36; p = 0.023) and in power (SMD 0.17; 95% CI 0.00, 0.34; p = 0.047). The subgroup analysis is the part that matters and is easy to get wrong: caffeine significantly improved **upper-body** strength (SMD 0.21; 95% CI 0.02, 0.39; p = 0.026) but **did not significantly improve lower-body** strength (SMD 0.15; 95% CI −0.05, 0.34; p = 0.147) — the lower-body confidence interval crosses zero. Effects are small even where significant, and the samples are predominantly male.
0.65
Meta-analysis of 10 studies (149 participants) on maximal muscle strength and 10 studies (145 participants) on muscle power. Caffeine produced a small but significant improvement in overall strength (SMD 0.20; 95% CI 0.03, 0.36; p = 0.023) and in power (SMD 0.17; 95% CI 0.00, 0.34; p = 0.047). The subgroup analysis is the part that matters and is easy to get wrong: caffeine significantly improved **upper-body** strength (SMD 0.21; 95% CI 0.02, 0.39; p = 0.026) but **did not significantly improve lower-body** strength (SMD 0.15; 95% CI −0.05, 0.34; p = 0.147) — the lower-body confidence interval crosses zero. Effects are small even where significant, and the samples are predominantly male.
Design Meta-Analysis (1.0) × quality 0.65 = impact 0.65
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Evidence
PRO (3)
PRO Meta-Analysis0.85 Grgic J, Grgic I et al. (2020)
Caffeine improved strength (ES 0.20), muscle endurance (ES 0.28), aerobic endurance (ES 0.22-0.45) and anaerobic power
Umbrella review of 21 meta-analyses covering endurance, strength, power, and sport-specific performance. Caffeine was found to improve muscle strength (ES: 0.20), muscle endurance (ES: 0.28), aerobic endurance (ES: 0.22-0.45), and anaerobic power. The evidence was consistent across meta-analyses, establishing caffeine as one of the most well-supported ergogenic supplements.
Weighted 0.85 — An umbrella review of 21 meta-analyses; no aggregate participant count is reportable, since pooling across overlapping reviews would double-count. Consistency across independent meta-analyses is exactly what makes it strong. Between 72% and 100% of pooled participants were men, which limits generalisability to women. No external funding.
British Journal of Sports Medicine
PRO Meta-Analysis0.85 Southward K, Rutherfurd-Markwick KJ et al. (2018)
Per the published Correction (44 studies): caffeine improved mean power output by 2.92 +/- 2.18% (ES 0.22 +/- 0.15) and time-trial completion time by 2.26 +/- 2.60% (ES 0.28 +/- 0.12) versus placebo, at moderate doses of 3-6 mg/kg. Responses were not uniform: 2 studies reported slower time trials and 5 reported lower mean power output on caffeine
Meta-analysis of caffeine and endurance time-trial performance. The figures below are those of the published Correction (doi 10.1007/s40279-018-0967-4), which supersedes the original article and restates the analysis as 44 included studies (the original said 46). Caffeine produced a small but evident benefit at moderate doses (3–6 mg/kg): mean power output improved by 2.92 ± 2.18% (effect size 0.22 ± 0.15) and time-trial completion time by 2.26 ± 2.60% (effect size 0.28 ± 0.12) versus placebo. The paper reports these as means ± standard deviations, not as pooled 95% confidence intervals. The response is not uniform — two studies reported slower time trials on caffeine and five reported lower mean power output — so the average effect conceals genuine non-responders.
Weighted 0.85 — k=46 studies. Pooled participant total is not stated in the accessible text, so sample_size is omitted rather than guessed, as is funding. A large, consistent meta-analysis with a clear dose-response and effects stable across exercise modalities -- strong within its class. Two caveats: a formal Correction was later published (doi 10.1007/s40279-018-0967-4), and the journal/DOI recorded in this file's front matter are wrong (the paper is Sports Medicine 48:1913-1928, doi 10.1007/s40279-018-0939-8, not BJSM).
Sports Medicine
PRO Meta-Analysisn=1490.65 Grgic J, Trexler ET et al. (2018)
Caffeine improved overall muscle strength (SMD 0.20; 95% CI 0.03-0.36; p = 0.023) and muscle power (SMD 0.17; 95% CI 0.00-0.34; p = 0.047). In subgroup analysis it significantly improved UPPER-body strength (SMD 0.21; 95% CI 0.02-0.39; p = 0.026) but NOT lower-body strength (SMD 0.15; 95% CI -0.05 to 0.34; p = 0.147)
Meta-analysis of 10 studies (149 participants) on maximal muscle strength and 10 studies (145 participants) on muscle power. Caffeine produced a small but significant improvement in overall strength (SMD 0.20; 95% CI 0.03, 0.36; p = 0.023) and in power (SMD 0.17; 95% CI 0.00, 0.34; p = 0.047). The subgroup analysis is the part that matters and is easy to get wrong: caffeine significantly improved upper-body strength (SMD 0.21; 95% CI 0.02, 0.39; p = 0.026) but did not significantly improve lower-body strength (SMD 0.15; 95% CI −0.05, 0.34; p = 0.147) — the lower-body confidence interval crosses zero. Effects are small even where significant, and the samples are predominantly male.
Weighted 0.65 — 149 participants pooled across 10 strength studies - a modest base, and the effect sizes are small (SMD 0.15-0.21), so the practical benefit is real but minor, and it is confined to upper-body strength; the lower-body estimate was not significant. Samples are predominantly male. No external funding and no competing interests declared. NOTE: the `doi` recorded here (10.1186/s12970-019-0269-0) does not resolve to this paper; the correct DOI is 10.1186/s12970-018-0216-0 (J Int Soc Sports Nutr 2018;15:11, PMID 29527137).
Funding: none declared
Journal of the International Society of Sports Nutrition