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

Ultra-endurance events expose athletes to extreme sleep deprivation exceeding 40 hours, compromising cognitive performance and safety through hallucinations, ataxia, and falls. This field study examined the effects of brief naps on perceived sleepiness and cognitive vigilance across three race editions (2022–2024), monitoring 52 completing runners. Participants relied primarily on subjective sleepiness (Karolinska Sleepiness Scale) rather than objective reaction time deficits (Psychomotor Vigilance Test) to trigger naps at checkpoints. Twenty-minute nap opportunities produced immediate reductions in subjective sleepiness one kilometer post-checkpoint. However, cognitive benefits emerged more gradually, with significantly faster reaction times observed only at the subsequent checkpoint, despite more than 40 hours of total sleep deprivation. Linear mixed-effects models confirmed robust circadian modulation of both sleepiness and reaction times, aligning with Borbély’s two-process model. Brief naps provided measurable cognitive protection without compromising race completion times, supporting their use as an effective preventive strategy against fatigue-related safety risks in extreme endurance contexts. These results highlight the importance of integrating structured, short nap opportunities into race and training guidelines, and more broadly into operational settings where sustained attention must be maintained under severe sleep loss.