The effect of different strategies used to reduce mental fatigue in small-sided volleyball games: Caffeine, mindfulness, carbohydrate, and napping interventi̇ons

The aim of this study was to examine the effects of different interventions applied after a mental fatigue (MF) protocol—caffeine mouth rinse (CAF), carbohydrate mouth rinse (CHO), mindfulness (MFN) exercise, and nap (NAP)—on psychophysiological responses and technical performance during 4 vs. 4 small-sided games in volleyball. Sixteen young female volleyball players (age: 15.43 ± 0.51 years) participated in the study. Prior to data collection, players were informed about the procedures, gave their consent, and underwent anthropometric measurements. Participants were randomized into groups and interventions. Video recordings were obtained during the games for technical performance analysis. Games were played with a 1-week interval, consisting of 4 sets of 4 minutes with 2 minutes of passive rest on a 4.5 × 12 m court. To induce mental fatigue, participants performed a 30- minute Stroop task via the Encephalapp mobile application before the games. Pre- and post- game assessments included the Brunel Mood Scale, NASA-TLX, and Trail Making Test. Following games, at the end of the first and fourth sets, players were administered the Visual Analogue Scale (VAS), Feeling Scale (FS), Rating of Perceived Exertion (RPE), as well as scales of exercise enjoyment, motivation, and arousal. Technical performance data (successful and unsuccessful forearm pass, successful and unsuccessful overhead pass, successful and unsuccessful spike, successful and unsuccessful setting) were obtained through video analysis. Findings showed no significant differences across groups in perceived exertion, feeling scale, arousal, motivation, and enjoyment (p > 0.05). However, CAF, MFN, and NAP significantly reduced mental fatigue on the VAS, while CHO was ineffective (p < 0.05). NASA-TLX results indicated no group differences for mental, temporal, or discomfort loads, but CAF and NAP significantly reduced physical and effort loads. On the Brunel Mood Scale, no significant differences were found for anger and depression. In contrast, surprise, fatigue, and vigor showed significant main effects of time and time*group interactions, indicating variation across interventions, while tension revealed only a significant main effect of time. Regarding technical performance, interventions had meaningful effects. In successful forearm passing, a moderate effect was found without significant group differences, whereas in unsuccessful forearm passing, strong effects emerged, with CAF and MFN more effective than CHO and control. For successful overhead passing, CHO was superior to MFN and control, while in unsuccessful overhead passing, all interventions outperformed control. In successful spiking, CAF, CHO, and MFN outperformed NAP; in unsuccessful spiking, CAF and CHO were more effective, and NAP also improved compared to control. In successful setting, only small effects were observed without significant group differences, while in unsuccessful setting, CAF and CHO outperformed MFN and NAP, and NAP improved compared to control. For the Trail Making Test, results demonstrated that in Test-A, both time and group effects were significant, with CAF and CHO improving performance compared to control. In Test-B, time, group, and time*group interactions were significant, with CAF, CHO, MFN, and NAP all significantly enhancing performance relative to control. In conclusion, this study demonstrated that CAF, MFN, and NAP interventions are effective in reducing mental fatigue, whereas CHO has limited impact. CAF and NAP significantly reduced physical and effort load. Mood states such as surprise, fatigue, and vigor varied depending on time and intervention. From a technical performance perspective, CAF, CHO, and NAP emerged as effective strategies, while Trail Making Test results confirmed that all interventions contributed to improved cognitive performance compared to control. Keywords: Mindfulness, Caffeine, Carbohydrate, Game-based training, Psychophysiology, Volleyball, Napping, Technical activity