4. Discussion
lower-body explosive, upper-body explosive
This study was conducted to investigate the effect of different doses of caffeine (3 and 6 mg/kg BW) on the performance of some physical (handgrip strength, vertical jump, agility, hand movement speed, and upper-body explosive power) and skill (attacking and serving) parameters of male volleyball players. The results of the study show that regardless of the dose, caffeine caused a significant improvement in the performance of the attack skill. However, agility showed a significant increase only after C6. Also, Sargent’s jumping performance and service skill in C6 increased significantly compared with C3 and PLA. In addition, there was no significant difference between C6, C3, and PLA in the performance of handgrip strength, upper-body explosive power, or hand movement speed. These findings suggest that a higher dose of caffeine compared with a lower dose may be more effective in movements requiring lower-body explosive power and the ability to change direction. Also, according to the findings, it seems that caffeine can lead to the improvement of complex skills, such as serving and attacking in volleyball.Previous studies have also shown the positive effects of caffeine on agility performance [Some mechanisms (central and peripheral) explain the improvement of agility and vertical jump performance induced by caffeine in the present study. For example, it has been shown that caffeine (due to its effects on the CNS) leads to increased activation of motor units [The findings have also shown that caffeine consumption improves performance in the volleyball attack test, regardless of the dose used. Also, volleyball serving performance increased after C6 compared with PLA or C3. Contrary to physical fitness parameters, there is very limited evidence about the effect of caffeine on volleyball-specific skill performance, especially service and attack accuracy. In addition, according to the knowledge of the authors, there is no study comparing the effect of different doses of caffeine and specific volleyball skills. However, in line with the findings of this study, it has been shown that caffeine gum consumption (at a dose of approximately 3 mg/kg body weight) improved attack accuracy [Improved accuracy in volleyball attack and serve performance after caffeine consumption may be related to neurocognitive mechanisms. In this regard, it has been shown that acute consumption of 3 mg/kg BW of caffeine decreased the reaction time to a simple stimulus, decreased the time required to hit a fixed target, and increased the accuracy of hitting the target in a shooting game [Also, this study showed that different doses of caffeine had no significant effect on upper-body explosive power, hand movement speed, or handgrip strength. However, the changes (relative percentage) compared with PLA showed that right handgrip strength (C3: 4.9% and C6:3.54%), upper-body explosive power (C3: 3.28% and C6: 3.38%), and hand movement speed (C3: 6.11% and C6: 6.02%) improved after caffeine supplementation. Consistent with these findings, A meta-analysis also showed that caffeine improved throwing performance with a small effect size, especially when the supplemental dose was ≤3 mg/kg BW [There were also limitations in this research. The main limitations of the current study were the lack of measurement of cognitive indicators, arousal, and other psychological variables affecting volleyball players’ function. Therefore, these cases should be corrected and controlled in future studies. Also, there was no control condition in the design of the present study, which may have hidden the effects of placebo or caffeine compared with the control. In addition, due to financial and time constraints, the authors of this study could not use the counterbalance design method to eliminate the order effect. Therefore, future studies should include the evaluation of these variables to expand on our findings.