Central Stimulation and Peripheral Optimization: The Impact of Caffeine and Beetroot Juice Supplementation and Co-supplementation on Physical Performance - Review

Abstract

Background: Supplementation with inorganic nitrates (NO₃^-) and caffeine (CAF) is a common practice in competitive sports. Despite the documented ergogenic effects of both substances, their potential synergy across different exercise models remains a subject of scientific debate.

Objective: The aim of this systematic review was to evaluate and compare the impact of isolated and combined CAF and NO₃^- supplementation on mechanical and physiological parameters in resistance and endurance tests.

Methods: The review was conducted according to PRISMA guidelines by searching PubMed and Scopus databases. Experimental studies on healthy adults, published primarily between 2021 and 2026, regarding the effects of supplementation on power, strength, muscular endurance, and aerobic capacity were analyzed.

Results: Nitrates improved muscular endurance 65% one repetition maximum (65% 1RM) and fatigue resistance in sprints without affecting power at maximum loads (1RM). Caffeine increased power at 75–100% 1RM (primarily in the lower body) and the number of repetitions at 65% 1RM. Co-supplementation (CAF + NO₃^-) showed a significant additive effect only in muscular endurance tasks. No synergy was found in time trials (TT) or cardiorespiratory parameters (VO₂, heart rate).

Conclusion: The combination of caffeine and nitrates is a highly effective strategy for high-volume anaerobic efforts but offers no additional benefits in traditional endurance tests. Optimizing results requires individualizing CAF dosage based on genotype and maintaining proper timing for nitrate intake.