1. Introduction
Background: The improvement of performance and skill indices of volleyball players can affect their success rate. Therefore, the present study aimed to evaluate the effects of acute caffeine supplementation of varied doses on collegiate volleyball players’ specific performance and skills. Method: This research was a randomized, double-blind, crossover design study in which 15 male volleyball players aged 18 to 25 years participated voluntarily. Participants were randomly placed in three different conditions, including 3 mg of caffeine per kilogram of body weight (C3), 6 mg of caffeine per kilogram of body weight (C6), and a placebo (PLA) with a one-week wash-out period between exercise trials. The supplement was taken 60 min before each exercise session. Ball throwing, hand movement speed, agility, Sargent’s jump and handgrip, and attacking and serving skill tests were measured and analyzed to check the performance and skill of the volleyball players. Results: This study showed a significant increase in agility test in C6 compared with the PLA condition (With the participation of volleyball in the Olympic Games and the holding of attractive competitions such as the World League, Nations League, and domestic leagues of countries, the importance of players’ performance in this popular sport is being noticed more than before [Caffeine is rapidly distributed in the body and affects the central nervous, respiratory, cardiovascular, and musculoskeletal systems [Since there is limited evidence on the acute effect of different doses of caffeine on the specific skill performance of volleyball players, as well as inconsistent results about the effects of caffeine dose on the bio-motor abilities related to volleyball, it seems necessary to conduct more studies on this matter. Therefore, this study investigated the effect of different doses of caffeine (3 mg/kg BW vs. 6 mg/kg BW) on the skill and physical performance of male volleyball players.