Do power naps save sleepiness? Cognitive benefits of brief sleep during a 100 miles ultramarathon

OBJECTIVES: This study aimed to investigate the effects of short naps on perceived sleepiness and cognitive vigilance during extreme sleep deprivation in ultra-endurance racing. It tested whether baseline cognitive performance predicts nap decisions and if 20-min naps enhance objective cognitive function while reducing subjective sleepiness. DESIGN: An observational field study was conducted during the 2022, 2023, and 2024 editions of the Ultra-Trail du Mont-Blanc® (170 km; ∼10 000 m elevation gain). METHODS: Sleep was recorded via wrist accelerometery for 52 completing runners (43.9 ± 8.3 years). Subjective sleepiness (Karolinska Sleepiness Scale, KSS) and reaction time (Psychomotor Vigilance Test, PVT) were assessed at five checkpoints (CP0-CP4). At CP1-CP3, participants chose between a 20-min sleep opportunity (nap group, NG) or remaining awake (awake group, AG). Measurements occurred at checkpoint entry (ENT) and 1 km post-checkpoint. RESULTS: Finishers slept an average of 28.4 ± 21.9 min. Linear mixed-effects models confirmed robust circadian modulation of both sleepiness and reaction times. Nap decisions were primarily driven by subjective sleepiness rather than objective vigilance deficits. While 20-min naps produced immediate reductions in KSS 1 km post-checkpoint, cognitive benefits (PVT) manifested more gradually, with significantly faster reaction times observed only at subsequent checkpoints. CONCLUSIONS: Brief naps serve as an effective reactive strategy to reduce perceived drowsiness and provide partial protection against late-race performance decline without compromising overall race completion times.