Caffeine mouth rinse fails to enhance jump and strength performance regardless of ingestion: a randomized crossover pilot trial in volleyball players

Purpose This study aimed to evaluate the effects of a caffeine mouth rinse (MR), administered alone or combined with ingestion, on vertical jump and maximal voluntary contraction (MVC) performance in volleyball athletes immediately and one hour after administration. Methods Seventeen male volleyball athletes completed a randomized, double-blind, placebo-controlled, crossover trial involving six sessions. Conditions included: control, placebo MR, caffeine MR (300 mg/25 mL), placebo MR+ingestion, and caffeine MR+ingestion. Participants performed countermovement jumps (CMJ), squat jumps (SJ), and MVC tests at two time points. Outcomes analyzed were jump height, power, peak force, time to peak force, peak rate of force development (RFD), and inter-limb MVC force difference. Results No condition demonstrated a significant ergogenic effect on jump performance or MVC. For the primary outcome (jump height), no main effect of condition was observed ( p > 0.05). A strong main effect of time indicated a performance decline after one hour across all conditions for jump height, power, and peak force (all p < 0.01). No significant Time × Condition interaction was found for any jump variable (all p > 0.05), confirming the performance decrease was similar regardless of supplement. Similarly, MVC force and inter-limb asymmetry remained unaffected by the interventions. Conclusion Caffeine MR, with or without concurrent ingestion, did not enhance vertical jump or maximal strength performance in volleyball athletes either immediately or one hour after administration. These findings should be considered preliminary and require confirmation in larger samples.