Addressing the Evidence Gap: Ergogenic Effects of Caffeine on Cycling Performance in Females-A Systematic Review and Three-Level Meta-Analysis

This systematic review and meta-analysis aimed to determine the effect of caffeine ingestion on female cycling performance. Three databases were systematically searched; studies were screened according to PICOS framework and PRISMA guidelines. Data were analyzed using a three-level meta-analytical model to account for the nesting of multiple performance outcomes within individual studies. Subgroup analyses assessed the influence of caffeine dose, training level, and menstrual cycle phase. Risk of bias was assessed using the RoB 2 tool; heterogeneity was assessed using the Q test and funnel plot analysis. Nineteen randomized crossover trials involving 235 females were included. The pooled analysis revealed a small and significant ergogenic effect of caffeine supplementation on cycling performance for females (standardized mean difference = 0.21; 95% confidence interval [0.11, 0.29]), with high certainty of evidence. Subgroup analysis showed a nonsignificant effect for caffeine dose (p = .79) and training level (p = .97), while caffeine significantly improved performance during the mid-luteal phase (standardized mean difference = 0.26; 95% confidence interval [0.06, 0.46]; p = .01) with no effect for other menstrual cycle phases (p > .11). Heterogeneity was nonsignificant, Q(36) = 7.99; p = 1.00, and overall risk of bias was rated as "some concerns." The limited clinical trials and inadequate menstrual cycle assessments preclude definitive conclusions regarding the effect of the menstrual cycle phases. These findings support the supplementation of caffeine to optimize performance in cycling for women.