Abstract
Anomalous perceptual experiences (APEs) have been reported anecdotally in ultra-endurance athletes. These experiences occur in the absence of psychiatric illness and may reflect the effects of extreme physiologic and environmental stressors. However, the literature is fragmented and terminology inconsistent, limiting understanding of the nature, prevalence, and mechanisms of these experiences. The aim of this study was to systematically review the literature describing APEs during ultra-endurance sport in an attempt to characterize their phenomenology, contextual features, and contributing factors. This review was registered prospectively (PROSPERO CRD420251079013) and conducted in accordance with PRISMA guidelines. A systematic search of Medline, Embase, and PsycINFO via the Ovid platform was completed in August 2025. Eligible studies reported APEs in adults participating in ultra-endurance sports lasting ≥6 h. Included studies were appraised for quality, and data were extracted for narrative synthesis. Fourteen studies met inclusion criteria: 4 case reports, 4 case series, 4 field studies, and 2 cross-sectional surveys. APEs were reported across diverse disciplines, including mountaineering, ultramarathon running, solo sailing, marathon volleyball, and dogsled racing. Experiences were commonly visual but also included auditory, somatic, and "sensed presence" phenomena. Sleep deprivation was the most consistent contributing factor, followed by exhaustion and low-light conditions. Symptoms typically emerged after ≥24 h of exertion, especially in darkness. Interpretations ranged from distressing to neutral or even supportive. No long-term psychiatric sequelae were reported. APEs appear to be transient nonpathologic phenomena triggered by extreme stress. Consistent terminology and categorization frameworks are needed. Findings have implications for athlete safety, event planning, and future research.