An interventional study of Mental Fatigue Induction and Control Condition in Mental Fatigue, Recovery and Volleyball, sponsored by Inonu University. Completed at 1 site in Turkey (Türkiye). Open to male participants aged 19 Years to 22 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-07-14.
Sponsored by Inonu University · Not applicable, Interventional, and Treatment
Mental fatigue is known to impair cognitive and physical performance in athletes, but the effectiveness of different nap durations in counteracting these effects remains unclear. The purpose of this randomized crossover study is to investigate the effects of mental fatigue and different nap durations (20, 40, 60, and 90 minutes) on volleyball-specific performance and electroencephalographic (EEG) activity in trained male volleyball players. Mental fatigue is induced using a 15-minute Stroop task. Performance outcomes include the Volleyball Agility Test (VAT) and Countermovement Jump (CMJ), while cortical activity is assessed using resting-state EEG recordings. The findings are expected to improve understanding of the neurophysiological mechanisms underlying mental fatigue and recovery and to provide evidence-based recommendations regarding optimal nap duration for athletes.
Mental fatigue has emerged as an important factor influencing athletic performance by impairing attention, executive function, decision-making, and motor performance. Volleyball is a sport requiring rapid cognitive processing, agility, explosive power, and precise motor control, making athletes particularly vulnerable to the detrimental effects of mental fatigue. Although daytime napping has been proposed as an effective recovery strategy, the optimal nap duration for restoring sport performance and brain activity following mental fatigue remains uncertain.
This study employs a randomized crossover repeated-measures design in which each participant completes six experimental conditions: Control, Mental Fatigue, Mental Fatigue followed by a 20-minute nap, Mental Fatigue followed by a 40-minute nap, Mental Fatigue followed by a 60-minute nap, and Mental Fatigue followed by a 90-minute nap. Mental fatigue is induced using a standardized 15-minute computerized Stroop task. A 72-hour washout period is maintained between consecutive experimental sessions.
Primary assessments include volleyball-specific agility performance, countermovement jump performance, and resting-state electroencephalographic (EEG) recordings obtained before and after mental fatigue and following the nap intervention. EEG analyses focus on spectral power in the delta, theta, alpha, and beta frequency bands as well as Theta/Alpha and Theta/Beta ratios.
The study aims to determine whether different nap durations differentially improve volleyball-specific performance and cortical activity following mental fatigue. The results are expected to provide practical recommendations for coaches and athletes regarding evidence-based recovery strategies while contributing to a better understanding of the neurophysiological mechanisms underlying mental fatigue and post-nap recovery.
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Exclusion Criteria:
Participants completed the control condition without mental fatigue induction or daytime nap intervention. A neutral documentary was viewed for 15 minutes. Resting-state EEG recordings, volleyball-specific agility performance, and countermovement jump performance were assessed according to the study protocol.
Other: Control Condition
Participants completed a 15-minute computerized Stroop task to induce mental fatigue. Following the mental fatigue protocol, resting-state EEG recordings, volleyball-specific agility performance, and countermovement jump performance were assessed.
Behavioral: Mental Fatigue Induction
Participants completed a 15-minute computerized Stroop task followed by a supervised 20-minute daytime nap. Resting-state EEG recordings, volleyball-specific agility performance, and countermovement jump performance were assessed after the nap intervention.
Behavioral: Mental Fatigue Induction · Behavioral: Daytime Nap 20 Minutes
Participants completed a 15-minute computerized Stroop task followed by a supervised 40-minute daytime nap. Resting-state EEG recordings, volleyball-specific agility performance, and countermovement jump performance were assessed after the nap intervention.
Behavioral: Mental Fatigue Induction · Behavioral: Daytime Nap 40 Minutes
Participants completed a 15-minute computerized Stroop task followed by a supervised 60-minute daytime nap. Resting-state EEG recordings, volleyball-specific agility performance, and countermovement jump performance were assessed after the nap intervention.
Behavioral: Mental Fatigue Induction · Behavioral: Daytime Nap 60 Minutes
Participants completed a 15-minute computerized Stroop task followed by a supervised 90-minute daytime nap. Resting-state EEG recordings, volleyball-specific agility performance, and countermovement jump performance were assessed after the nap intervention.
Behavioral: Mental Fatigue Induction · Behavioral: Daytime Nap 90 Minutes
Mental fatigue was induced using a standardized 15-minute computerized Stroop Color-Word Task designed to increase cognitive load and induce mental fatigue before performance and EEG assessments.
Participants watched a neutral documentary for 15 minutes without mental fatigue induction or daytime nap intervention before EEG and performance assessments.
Participants underwent a supervised 20-minute daytime nap following mental fatigue induction in a quiet, darkened room before post-intervention EEG and performance assessments.
Participants underwent a supervised 40-minute daytime nap following mental fatigue induction in a quiet, darkened room before post-intervention EEG and performance assessments.
Participants underwent a supervised 60-minute daytime nap following mental fatigue induction in a quiet, darkened room before post-intervention EEG and performance assessments.
Participants underwent a supervised 90-minute daytime nap following mental fatigue induction in a quiet, darkened room before post-intervention EEG and performance assessments.
EEG Spectral Power
Resting-state electroencephalographic (EEG) activity was recorded from the Fz, Cz, Pz, O1, and O2 electrode sites. Power spectral density was analyzed for the delta (1-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), and beta (13-30 Hz) frequency bands. All frequency-band power values were expressed in microvolts squared per hertz (µV²/Hz).
Time frame: At baseline, immediately after the mental fatigue task, and immediately after completion of the assigned intervention during each experimental session.
EEG Theta/Alpha Ratio
The theta-to-alpha power ratio was calculated from resting-state EEG recordings obtained from the Fz, Cz, Pz, O1, and O2 electrode sites by dividing theta-band power by alpha-band power. The outcome was expressed as a unitless ratio.
Time frame: At baseline, immediately after the mental fatigue task, and immediately after completion of the assigned intervention during each experimental session.
EEG Theta/Beta Ratio
The theta-to-beta power ratio was calculated from resting-state EEG recordings obtained from the Fz, Cz, Pz, O1, and O2 electrode sites by dividing theta-band power by beta-band power. The outcome was expressed as a unitless ratio.
Time frame: At baseline, immediately after the mental fatigue task, and immediately after completion of the assigned intervention during each experimental session.
Volleyball-Specific Agility Performance
Volleyball-specific agility performance was assessed using the Volleyball Agility Test (VAT). Performance was quantified as test completion time (seconds), with lower values indicating better agility performance.
Time frame: Immediately after completion of each experimental protocol.
Countermovement Jump Height
Countermovement jump (CMJ) performance was assessed using the My Jump Lab application by measuring jump height in centimeters (cm), with higher values indicating better jump performance.
Time frame: Immediately after completion of each experimental protocol.
Countermovement Jump-Derived Mechanical and Kinematic Parameters
Countermovement jump (CMJ)-derived mechanical and kinematic parameters were obtained using the My Jump Lab application from the CMJ assessment performed at the end of each experimental protocol. Participant jump height and body mass were entered into the application's manual data-entry module, which provided flight time (ms), average velocity (m/s), take-off velocity (m/s), and impulse (kg·m/s). These parameters were analyzed as complementary derived measures of CMJ performance.
Time frame: Immediately after completion of each experimental protocol.
Pittsburgh Sleep Quality Index (PSQI) Score
Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI), a validated self-reported questionnaire that evaluates sleep quality over the previous month. The PSQI consists of 19 self-rated items yielding a global score ranging from 0 to 21, with higher scores indicating poorer subjective sleep quality.
Time frame: Baseline (before the first experimental session).
Visual Analog Scale (VAS) Score for Perceived Nap Quality
Perceived nap quality was assessed using a 100-mm Visual Analog Scale (VAS). Participants rated the overall quality of their daytime nap on a horizontal line ranging from 0 mm (very poor nap quality) to 100 mm (excellent nap quality). Higher scores indicate better perceived nap quality.
Time frame: Immediately after each daytime nap intervention (20-, 40-, 60-, and 90-minute nap conditions).
Plan to share: No — Individual participant data will not be shared because the study includes a small sample size, and no data-sharing plan was included in the approved study protocol or informed consent. Aggregate study results will be reported in scientific publications.
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Inonu University