Strategic Daytime Napping Enhances Agility and Lowers Perceived Exertion But Does Not Improve Fatigue Resistance in Adolescent Soccer Players

repeated-measures crossover design was conducted to examine the acute effects of strategic daytime naps on anaerobic performance in competitive male soccer players. Sixteen players from the Yeni Malatyaspor U17 and U19 teams participated voluntarily. Each participant completed three test sessions under randomized conditions: no nap (N0), 25-minute nap (N25), and 45-minute nap (N45), with a 48-hour recovery period between sessions.

Before testing, all participants underwent familiarization sessions to adapt to nap protocols and performance tests. The nap sessions were held in dark, quiet rooms maintained at ~22°C. Fitbit Charge 6 devices objectively verified nap compliance and duration. Participants abstained from caffeine, alcohol, and strenuous activity for at least 24 hours before testing.

To minimize sleep inertia, physical performance testing began 60 minutes after awakening. The test battery included the Pro Agility Test (to assess change-of-direction speed) and the Repeated-Sprint Ability (RSA) Test (6 × 30 m sprints with 20-second recovery). Heart rate during warm-up and ratings of perceived exertion (RPE) were recorded for standardization and subjective effort assessment.

Subjective measures included the Morningness-Eveningness Questionnaire (MEQ), Hooper Index, Pittsburgh Sleep Quality Index (PSQI), Profile of Mood States (POMS), and Visual Analogue Scales (VAS) for sleep quality and alertness. All players were identified as intermediate chronotypes according to the MEQ.

Anthropometric measurements (height, weight, BMI) were obtained using standardized equipment. Statistical analyses were conducted with SPSS v29, using repeated-measures ANOVA with Bonferroni correction to compare conditions. Effect sizes (ηp², Cohen's dz) and correlations between psychological and performance variables were calculated.