Effects of mental fatigue and different nap durations on volleyball performance and brain activity

Purpose: The aim of this study was to examine the effects of mental fatigue on agility performance, jump performance, and electroencephalographic (EEG) activity in volleyball players, and to evaluate the role of different nap durations (20, 40, 60, and 90 min) in mitigating these effects. Material and Method: Ten male volleyball players (mean age: 20.60±0.97 years) voluntarily participated in the study. A randomized crossover repeated-measures experimental design was employed. Participants completed six different protocols: control (CON), mental fatigue (MF), 20-min nap (NAP20), 40-min nap (NAP40), 60-min nap (NAP60), and 90-min nap (NAP90). Mental fatigue was induced using a 15-min Stroop Test. Performance assessments included the Volleyball Agility Test (VAT) and Countermovement Jump (CMJ). EEG data were recorded using the Emotiv EPOC Flex system from the Fz, Cz, Pz, O1, and O2 electrode sites. Data were analyzed using the Friedman and Wilcoxon Signed-Rank tests. Results: Mental fatigue impaired agility performance by increasing the Volleyball Agility Test (VAT) time from 7.09 ± 0.46 s to 8.02 ± 0.52 s (p < 0.001). Across all nap-opportunity conditions, agility performance was better than under the mental fatigue condition, with significant differences observed in pairwise comparisons (p < 0.05). Countermovement jump (CMJ) height decreased from 55.98 ± 1.64 cm to 52.65 ± 1.32 cm following mental fatigue (p < 0.05). Only the 20-min nap-opportunity condition produced a significant recovery in CMJ performance, increasing jump height to 57.56 ± 2.71 cm (p < 0.05). EEG analyses revealed significant changes in the delta and alpha frequency bands over the frontal, parietal, and occipital regions, as well as significant alterations in the Theta/Alpha and Theta/Beta ratios in selected protocols (p < 0.05). Conclusion: Mental fatigue negatively affects volleyball-specific agility and jump performance. Nap-opportunity conditions appear to support recovery, particularly in agility performance, whereas recovery in jump performance varies according to nap duration. EEG findings further suggest that changes observed in selected cortical regions following short-duration nap opportunities may be associated with the observed performance outcomes.