Placebo effects of caffeine on sport performance: a systematic review and meta-analysis
Study Details
This systematic review and meta-analysis included 17 studies and 257 participants, examining the effect of giving athletes a placebo while telling them it was caffeine 🔍
Key findings ⬇️
Key Findings
☕ Across primary performance outcomes, “placebo caffeine” produced a small-to-moderate improvement versus baseline (d = 0.49)
⏱️ The largest pooled effect was for time to exhaustion (d = 1.07), although this was based on only 2 studies
😮💨 Perceived exertion improved moderately (d = 0.52), suggesting expectation may make exercise feel easier
🏋️ Placebo caffeine also increased repetitions performed (d = 0.48) and total weight lifted (d = 0.73)
↔️ Effects on power output, velocity, heart rate, lactate and oxygen consumption were not significant
🧠 Placebo effects were larger when researchers were blinded to whether participants had actually received caffeine, suggesting researcher expectations may also influence outcomes
📣 Using more strategies to reinforce the belief that caffeine would improve performance was associated with larger reductions in RPE
🙋♂️ Effects appeared larger in studies with fewer women, but 82% of participants were male, making sex differences highly uncertain
📊 Between-study heterogeneity was low (I² = 21%), and results were not driven by any single study
⚠️ However, 9/17 studies were high risk of bias and the remaining 8 had unclear risk, resulting in low overall certainty
Conclusion
Interestingly, the pooled placebo effect (d = 0.49) sits within the range previously reported for actual caffeine, suggesting some of caffeine’s ergogenic effect may come from expectation alongside its pharmacological effects 🧐
For athletes, believing caffeine will work may meaningfully contribute to its performance benefit, so familiarisation, positive expectations and a consistent caffeine routine could help maximise the effect of actual caffeine use ✅
Reference
https://pubmed.ncbi.nlm.nih.gov/42897966/
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