Dose-dependent effect of caffeine supplementation on judo-specific performance and training activity: a randomized placebo-controlled crossover trial

Randomized, double-blind, placebo-controlled crossover trial in 22 healthy, highly trained male judoists from Polish clubs. Participants had at least 4 years of training experience and trained at least four times per week; habitual caffeine use was categorized as consumers or non-consumers.

Acute caffeine supplementation was tested at 3, 6, and 9 mg/kg body weight, administered orally as pure pharmaceutical caffeine dissolved in 350 mL water 60 minutes before testing. Placebo was maltodextrin. Each participant completed all treatments in a randomized, double-blind, placebo-controlled crossover design with a 7-day washout between sessions.

Overall, caffeine improved judo-specific performance, but the effect was dose dependent. Total throws in the Special Judo Fitness Test improved with caffeine (χ2 = 28.03, P < 0.001, W = 0.32), with 6 and 9 mg/kg performing better than 3 mg/kg, placebo, or baseline, and 9 mg/kg exceeding 6 mg/kg. In Randori, total attacks also improved (F = 2.81, P = 0.047, η2p = 0.12); 9 mg/kg was higher than baseline or placebo, and 6 mg/kg was higher than placebo but similar to baseline. Habitual caffeine use moderated the response: among caffeine consumers, only 9 mg/kg clearly increased total throws, whereas among non-consumers, 6 mg/kg and 9 mg/kg improved SJFT performance versus baseline, 3 mg/kg, or placebo. Three mg/kg showed no positive effect, SJFT Index did not differ across doses, and perceived exertion was unchanged.

Small sample size and male-only population limit generalizability. The study was acute and sport-specific, so findings may not extend to other populations, training states, or longer-term supplementation. Habitual caffeine use was categorized rather than directly quantified in detail, and adverse events were not reported.