Effects of Acute Caffeine Supplementation on Performance and Physiological Responses in CrossFit: A Systematic Review and Three-Level Meta-Analysis

Objectives: We quantified the influence of acute caffeine (CAF) supplementation on CrossFit performance and physiological outcomes and examined potential effect modifiers. Methods: Randomized crossover studies involving CAF supplementation in CrossFit were identified through systematic searches of multiple electronic databases. Performance effect sizes were expressed as Hedges' g and pooled within a three-level random-effects framework, while physiological outcomes were synthesized using conventional two-level models. Effect modification was examined across training status (recreationally active vs. trained) and CAF delivery form (capsule vs. beverage). Meta-regression was additionally used to assess whether relative CAF dose was associated with changes in CrossFit performance. Results: The final synthesis comprised seven studies with 103 participants, including 13 women. A small favorable effect of CAF was found for overall CrossFit performance (g = 0.13, 95% CI: 0.05-0.22), accompanied by a higher blood lactate concentration (g = 0.53, 95% CI: 0.23-0.82). Stratified estimates favored CAF in recreationally active participants (g = 0.20, 95% CI: 0.06-0.34) and when administered in capsule form (g = 0.17, 95% CI: 0.06-0.29); nevertheless, evidence for between-subgroup differences was absent (all p subgroup > 0.05). The relative CAF dose did not explain variation in performance effects in either the linear (β1 = 0.04, p = 0.570) or nonlinear model (β2 = -0.004, p = 0.578). Conclusions: The available evidence suggests a small ergogenic benefit of acute CAF supplementation for selected CrossFit performance outcomes, accompanied by elevated blood lactate concentrations. Subgroup analyses revealed no significant moderating effect of training status and supplementation protocols. However, the limited number of studies and predominance of male participants warrant cautious interpretation. Future research should prioritize larger randomized controlled trials, greater representation of female athletes, and more standardized CrossFit performance protocols.