Comparing Acute Effects of Caffeine Delivery Forms on Cross-Training Performance: A Randomized Placebo-Controlled Crossover Trial

<b>Background/Objectives</b>: The aim of this study was to compare the different forms of caffeine (CAF) administration in CrossFit^® participants. The countermovement jump (CMJ), the rate of perceived exertion (RPE), the total number of repetitions, and the maximum (HR_max) and mean heart rate (HR_mean) were evaluated. <b>Methods</b>: Fourteen males with more than six months of continuous CrossFit^® training (30.9 [5.62] years, 179 [1.33] cm, 78 [5.75] kg, 24.3 [1.33] kg·m^-2) participated in this randomized, placebo-controlled, crossover study. Participants were randomized in a repeated measures design using caffeine capsule (CC), caffeine chewing gum (CCG), and caffeine mouth rinse (CMR) protocols, along with a placebo group (PG). Participants were unaware of whether any of the delivery methods contained caffeine. A 7-day washout period before each crossover was used. To ensure ecological validity, we replicated the real-world practice of CAF ingestion 30 min prior to training, mirroring typical athlete pre-workout routines. The participants of CrossFit^® performed the 'Cindy' protocol, and the CMJ as a primary outcome was measured pre- and post-intervention, while the RPE, HR, and the number of repetitions were tracked at the end of the workout for comparisons. <b>Results</b>: No significant differences were found between CAF forms in internal load measures (RPE, HR_max, HR_mean) or the number of repetitions. While no changes were observed with other CAF forms, CMR significantly improved the CMJ performance compared to the baseline (Δ: +3.5; Cohen's d_unb: 0.51], which exceeded the estimated SWC by approximately three-fold. However, the inferential analysis revealed no significant main effects of the caffeine administration method on any measured outcomes. <b>Conclusions</b>: While CAF delivery forms did not improve internal load measures or performance parameters, such as the RPE, HR, or the total number of repetitions, the caffeine mouth rinse (CMR) showed a potentially meaningful improvement in CMJ performance after CrossFit^® training in participants with a certain level of experience.