Sage Journals: Discover world-class research

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.

Keywords

hallucinations psychosis endurance athlete

Introduction

Who is the third who walks always beside you?

When I count, there are only you and I together

But when I look ahead up the white road

There is always another one walking beside you

Gliding wrapt in a brown mantle, hooded

I do not know whether a man or a woman

—But who is that on the other side of you?

Excerpt from “The Waste Land” by T. S. Eliot.¹

The lines were stimulated by the account of the Antarctic expeditions (I forget which, but I think one of Shackleton's): it was related that the party of explorers, at the extremity of their strength, had the constant delusion that there was one more member than could actually be counted.

Footnote to “The Waste Land” by T. S. Eliot.¹

Ultra-Endurance Sport

In the scientific literature, endurance sports are typically defined as continuous physical activities lasting more than 30 min, a threshold based on the physiologic definition of endurance—the muscle's ability to sustain force or repeated contractions over time. However, Zaryski and Smith proposed that endurance can be understood from both physiologic and psychological perspectives, suggesting a minimum duration of 6 h to characterize ultra-endurance activity.² This extended definition has since been adopted by subsequent researchers.³ As participation trends increasingly favor longer-duration athletic events,⁴ the cultural and popular understanding of endurance sport appears to be converging with the scientific definition of ultra-endurance.

Anomalous Perceptual Experiences

Anomalous perceptual experiences (APEs) refer to disruptions in perception that can arise in individuals regardless of whether they have a psychiatric diagnosis.⁵ These experiences may affect any sensory system and typically involve either altered interpretation of real stimuli or the perception of stimuli that are not present, such as hallucinations.⁶

The continuum model of psychosis proposes that such perceptual anomalies lie along a spectrum of psychotic symptoms, varying in both severity and form.⁷ At the severe end, they are characteristic of clinical conditions such as schizophrenia.⁸ However, milder forms of these experiences are also observed among individuals in the general population who do not meet criteria for a psychotic disorder.⁹

APEs During Ultra-Endurance Sport

Ultra-endurance sports demand prolonged physical exertion under conditions of physiologic stress, sleep deprivation, and extreme environmental exposure. These conditions are known to alter perceptual functioning, sometimes profoundly.^10,11 A growing body of anecdotal and scientific literature reports a range of APEs in ultra-endurance athletes.

Examples range from the early expedition accounts of polar explorers such as Sir Earnest Shackleton, who experienced a third person “sensed presence” phenomenon (which later inspired T. S. Elliot, as quoted in the Introduction),¹² to contemporary accounts from recreational runners in the popular magazine Runners World: “In the latter stages of races, I have seen tree roots turning into snakes trying to trip me up and, more pleasurably, tables adorned with red wine.”¹³ While few studies have quantitatively assessed the prevalence of APEs in ultra-endurance athletes, there is a large body of anecdotal accounts in magazines, internet forums, and other lay literature that suggest that such experience may be common.^13–15

Psychiatric symptoms are characterized primarily through subjective reports; the clarity and consistency of phenomenological terms are especially important. At present, there is a risk that these phenomena are being retrofitted into established diagnostic categories rather than being used to shape new theoretical understandings. It remains unclear whether such experiences should be viewed as harmless by-products of extreme physical exertion, early manifestations of conditions such as high altitude cerebral edema or as distinct altered states of consciousness in their own right.

There is also a risk that symptoms are being attributed to causative factors relative to a single sporting discipline. For example, Hüfner et al attempted to define a syndrome of psychosis in mountaineers occurring at high altitude.¹⁶ However, if they had considered the wider ultra-endurance athlete population, they may have found similar phenomena occurring outside of high altitude environments, for example, in solo sailors breathing oxygen-rich air at sea level.¹⁷

Despite widespread anecdotal reports of APEs in ultra-endurance athletes, fundamental questions persist regarding their prevalence, phenomenology, contributing factors, and broader significance. It remains unclear whether APEs represent a normal feature of extreme exertion or a pathologic state with implications for athlete performance, safety, and long-term health and well-being. Ultra-endurance sport provides an unusual natural laboratory in which human perception can be studied under threshold conditions, potentially providing insights relevant to other states of extreme stress. Developing a more comprehensive and structured understanding of APEs across multiple ultra-endurance sporting disciplines would provide a good starting point to help identify shared phenomena and contributing factors.

Objective

The aim of this systematic review was to examine the existing peer-reviewed literature on APEs during ultra-endurance sport with a focus on characterizing the types of APEs, the context in which they occur, and possible contributing factors.

Methods

This systematic review was prospectively registered (PROSPERO CRD420251079013) and is reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses x(PRISMA) guidelines.¹⁸ Ethical approval was not required because the study provided a secondary summary of existing published data.

Inclusion and Exclusion Criteria

The inclusion and exclusion criteria for this review were developed using the Population, Interest, Comparison, Outcome, and Study design (PICOS) framework, which provides a structured approach to defining eligibility in systematic reviews:

Population: Adults (aged ≥18 y) engaged in ultra-endurance sports of duration ≥6 h.

Excluding: Simulated sports (eg, lab-based virtual reality; studies of participants with diagnosed psychiatric disorders unless part of a mixed sample)

Interest: APEs occurring during ultra-endurance sport

Comparison: Not applicable due to the primarily descriptive and exploratory nature of the included studies

Outcome: The characteristics and contexts of APEs

Excluding: Studies that report general fatigue, affective symptoms, or cognitive performance without reference to APEs

Study design: Peer-reviewed studies published in English

Excluding: Animal studies, abstracts, letters to the author without full text data, and review articles

Information Sources

A systematic search of Medline, Embase, and PsycINFO was undertaken in August 2025 using the Ovid platform. In addition to this primary database search, references of included studies were searched manually and full-text articles were sourced if they met the criteria for inclusion.

Search Strategy

A comprehensive search strategy was developed in consultation with Christy Ballard, a subject-specific research librarian. Due to the considerable variability in terminology used across the literature to describe APEs, the search strategy required careful refinement and complexity to ensure comprehensive retrieval of relevant studies. Care was taken to be inclusive in the “ultra-endurance sport” arm of the search to minimize bias. For example, the main author is a climber, distance runner, and mountaineer—consultation with Christy Ballard ensured that other sports, such as solo sailing, motorsports, and deep-sea diving, were not unconsciously excluded. The search strategy was adapted for each database to account for differences in indexing, thesauri, and search functionalities. No date limits were applied, but results were restricted to humans and the English language. Full search strategies for each database are provided in the online Appendices 1 to 3 and are summarized in brief below.

Population/Activity Terms

Endurance, endurance athlete, endurance sport, endurance event, endurance training

Ultra-endurance, ultramarathon

Sport—plus specific sport types according to the database in question and common colloquially described ultra-endurance sports

Altitude, mountaineering (not routinely included under sport but known to be a key area of research)

Outcome Terms

Psychosis, psychotic

Hallucinations, illusions, perceptions, misidentification

Delusions, paranoia

Delirium

Study Selection

Search results were imported into Rayyan, an open-access software tool designed to facilitate systematic reviews.¹⁹ Duplicates were removed prior to screening. Authors EED and SLD independently screened titles and abstracts for eligibility. Any disagreements were resolved through discussion, and PG served as an adjudicator where consensus could not be reached.

Data Extraction and Quality Assessment

Data relevant to the key themes were extracted independently by EED and SLD under the following headings: Author(s), Title, Year, Study design, Participant(s), Ultra-endurance sport, Measurement(s), APEs, and Key findings. The data extraction began on August 7, 2025 and took 2 d. Assessing the quality of included studies posed a challenge because there was no restriction on study type. Thus, for case reports and case series, the corresponding Joanna Briggs Institute checklist was used.^20,21 The National Institutes of Health Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies was used for the remaining articles.²² See online Appendices 4 to 6for the checklist (Figure 1).

Figure 1.

PRISMA flow diagram.

Results

Overview of Included Studies

Fourteen studies were included in this review, comprising a mixture of case reports (n=4), case series (n=4), field studies (n=4), and cross-sectional surveys (n=2). The ultra-endurance sports examined included mountaineering (n=6), ultramarathon running (n=5), dogsled racing (n=1), solo sailing (n=1), and marathon volleyball (n=1). Studies are summarized in Table 1.

Table 1.

Summary of Included Studies.

Author(s)	Aim	Population	Study Design and Measures	Key Findings
Garrido and Hüfner (2023)²⁹	To report a third-person hallucination in a professional mountaineer	N=1 male mountaineer	Case report	Visual and sensed presence APEs at an altitude of 7500 m
Hoffman et al (2018)³⁵	To describe rescue enabled by GPS tracking during an ultramarathon event	N=1 male ultramarathon runner	Case report	Visual APEs during third day of race, leading to getting lost and requiring rescue
Firth and Bolay (2004)²⁷	To describe neurologic dysfunction at high altitude	N=1 male mountaineer	Case report	Sensed presence and somatic APEs at an altitude of 6700 m
Windsor (2008)³¹	To describe an account of sensed presence on Mount Everest	N=1 male mountaineer	Case report: author's personal account	Complex sensed companion, visual, and auditory APEs at an altitude of 8200 m
Lund (1985)³⁷	To describe symptoms following prolonged sports performance	N=12 male volleyball players	Case series: interviews, medical exam, bloods, urine	All players experienced visual APEs, resulting in gameplay being stopped prematurely
Popkin et al (1981)³⁶	To examine behavioral responses during prolonged competitive stress	N=5 male dogsled racers	Case series: interviews, mental state examination, bloods, urine	Four participants reported visual APEs, most frequently at dusk or dawn
Brugger et al (1999)³⁰	To investigate APEs in extreme altitude climbers	N=8 mountaineers, 7 male, 1 female	Case series: retrospective report with structured interview	Seven participants reported somatic, visual, and auditory APEs
Hüfner et al (2018)³²	To assess the frequency of high altitude psychosis in lay literature	N=60 mountaineers, 49 male, 11 female	Case series: autobiographical accounts in the lay literature	APEs described in 48 of the 83 accounts: sensed presence, visual, auditory, illusions, depersonalization, and somatic
Hüfner et al (2021)²³	To evaluate psychotic symptoms at high altitude	N=97 mountaineers, 75 male, 22 female	Field study: multiple questionnaires and brief clinical examination	Ten participants endorsed ≥1 psychotic symptom on HAPSY-Q; 18 participants endorsed ≥1 symptom on PQ-16 One participant met M.I.N.I criteria for psychosis
Hurdiel et al (2015)³⁴	To gain insight into sleep deprivation's effect on cognitive performance during a 168-km ultramarathon	N=17 ultramarathon runners, 16 male, 1 female	Field study: 10-min serial response time test, wrist-worn actigraphy, questionnaire immediately after the race	Four participants reported visual APEs occurring from the second night of the race
Huang et al (2021)²⁵	To gain insight into visual hallucinations during a mountain ultramarathon	N=8 ultramarathon runners, 6 male, 2 female	Field study: questionnaires, blood samples	Three participants had visual APEs in the final 60 km of the race, all occurring in tunnels
Hurdiel et al (2012)³³	To examine sleep and functional impairment in solo sailors	N=16 solo sailors, 13 male, 3 female	Field study: diary, semistructured interviews	Five episodes of APEs reported, 4 auditory, 1 visual
Carbone et al (2020)²⁶	To bring clarity to the analysis of misperceptions reported by athletes	N=21 ultramarathon runners, 20 male, 1 female	Cross-sectional survey: phenomenological questionnaire	Eleven participants experienced illusions, 8 experienced hallucinations, 2 experienced “anomalies in intrinsic characteristics of perception”; modalities included visual, auditory, somatic, and sensed presence
Kishi et al (2024)²⁴	To investigate sleep and the repercussions of sleep deprivation in ultramarathons	N=1154 ultramarathon runners, 989 male, 165 female	Cross-sectional survey: survey on sleep and potential repercussions	34% reported hallucinations, modality not specified

APE, Anomalous perceptual experience.

Types of APEs

Included studies reported a range of APEs of different modalities. Two studies did not describe the sensory modality of the APEs, reporting them only as “psychotic symptoms”²³ and “hallucinations.”²⁴ Visual phenomena were the most frequently reported, described in 11 of the 14 studies. These ranged from distorted stones²⁵ to complex scenes of a runner's family members accompanying them during the race.²⁶ Only 1 study did not report visual phenomena.²⁵

The experience of a “sensed presence”—a feeling or sense that another entity, individual, or being is present despite no clear sensory or perceptual evidence²⁸—was reported in 7 studies.^{25–27,29–32} When quotes were present, they painted a rich perceptual experience: “I noticed an intense presence of two beings . . . a great sense of calm came over me. Those unexpected saviours, whose figure I did not perceive at any time, were companions.”²⁹

The next most common APEs were auditory phenomena, reported in 5 studies^26,30–33 Phenomena included examples such as hearing ringing bells,³⁰ talking to Buddha and Gandhi,²⁶ and receiving instruction from a perceived companion.³¹

Somatic, tactile, and proprioceptive phenomena were difficult to separate due to inconsistent definitions. As a group, they were reported in 5 studies.^{26,27,30–32} Examples include “While walking, he felt as if his legs were moving of their own accord and his torso was elongated. He felt detached from his person, as if he were observing himself from a distance.”²⁵ Among them, the 7 mountaineers in a study by Brugger et al reported “misperception” of one's own body in space; “illusions” of floating, moving like an automaton; and separation from one's body.³⁰ Although no description was given, Hüfner et al categorized “hallucinations somesthetic” and “depersonalization” in participants.³² There also was 1 report of distorted perception of time.³⁰

Contributing Factors

Several studies centered their investigations on a hypothesized contributing factor, with altitude being the most commonly explored. Altitude was the focus of the 6 studies of mountaineers^{23,27,29–32} and 1 study of ultramarathon runners.²⁶ Sleep deprivation was another prominent topic of investigation. Hurdiel et al explored the effect of sleep during an ultramarathon³⁴ and during solo sailing races.³³ Kishi et al explored the patterns, strategies, and repercussions of sleep during an ultramarathon.²⁴

Sleep deprivation emerged as the most consistently reported contributing factor across studies, even when it was not the primary focus of investigation. Notably, only Hüfner et al did not identify sleep deprivation as a contributing factor in either of their studies.^22,32 Perhaps most striking was an ultramarathon runner sleeping for just 10 min in more than 70 h of race time.³⁵ The ultra-endurance sports lasting multiple days also showed significant sleep deprivation; dogsled racers reported just a few hours of sleep over the final few days of a 2-wk race.³⁶

Exhaustion (defined loosely as both physical and/or mental) was a commonly identified contributing factor across studies, which is unsurprising given that the shortest reported event involved an average of 33.6 h of ultramarathon running,²⁴ whereas the longest was a 16-d, 7-h, and 10-min dogsled race.³⁶ Although the total duration of mountaineering expeditions was not always specified, it can be reasonably inferred that participants experienced prolonged exertion prior to the APEs. For instance, Windsor described a 3-mo expedition culminating in a 10-h summit push on Mount Everest, during which his APEs occurred.³¹

Several studies identified a temporal pattern in the onset of APEs. Visual phenomena were reported to begin on Day 3 of racing in an ultramarathon runner,³⁵ during the final 60 km of a 246-km ultramarathon,²⁵ and on Day 3 of a 356-km ultramarathon.²⁶ In a mountaineering context, 1 individual experienced the onset of APEs on Day 10 of the expedition.²⁷ Supporting this temporal pattern of APEs occurring after multiple days of exertion, Hurdiel et al found a statistically significant increase in the likelihood of APEs the longer solo sailors had been racing.³³

Sensory deprivation was another frequently reported contributing factor, typically arising from low-light conditions. APEs were most commonly reported during night-time activity among dogsled racers and ultramarathon runners^34,36 as well as mountaineers.^29,31 Similarly, Huang et al found that all reported APEs among ultramarathon runners occurred when they were passing through tunnels.²⁵

Other potential contributing factors were social isolation,^29,30,33,36 starvation,^{29,30–32,36,37} dehydration,^{29,30,35–37} cold,^{27,29,31,32,35,36} danger,^29,32,36 challenging terrain,^26,34,35 wind,^31,36 and caffeine ingestion,^26,36 although of note, Hüfner et al found caffeine to be protective.²³ Contributing factors often occurred simultaneously, and several studies speculated that this may support a cumulative threshold model for the emergence of APEs.

Functional Impact

The impact of APEs on the athletes’ performance and well-being varied from comforting and helpful^29,31 to leading to distress and error in or cessation of the sport.^23,35,37 Hüfner et al reported that APEs were perceived as neutral in 60%, helpful or comforting in 23%, and frightening or dangerous in 17% of participants.³² The ultramarathon runners in the cross-sectional survey of Carbone et al described a range of APEs that, on the one hand, caused emotional distress (eg, sinister interpretation of environmental stimuli such as clouds, rocks, bushes, or trees as beasts) and, on the other hand, were comforting and helpful (eg, including family members accompanying a participant for several kilometers, entertaining them with extended conversations, and giving advice on how to complete the race and how to face adversity).²⁴

Causative Pathology

Several studies proposed potential neurobiologic or psychopathologic mechanisms underlying APEs in ultra-endurance athletes. These were universally acknowledged to be highly speculative.

Firth and Bolay hypothesized that the consistent reports of a “sense of presence” among mountaineers may represent a reproducible complication of extreme altitude. They suggested that dysfunction in the parietal or temporal cortex, particularly near the right angular gyrus, could underlie these experiences.²⁷ This hypothesis also was discussed by Hüfner et al, who proposed that hypoxia-induced alterations in cortical function, especially in the parietal and temporal lobes, may contribute to perceptual disturbances.³² Carbone et al similarly considered dysfunction in these cortical regions and their associated limbic structures, positing that reduced cerebral perfusion in hypoxic conditions may disrupt sensorimotor integration. They further suggested that such disruptions could serve as early markers of global cerebral hypoxia.²⁶

Furthermore, Hüfner et al speculated that hypoxia may elevate central dopamine and serotonin levels, contributing to altered perception. They noted that high altitude cerebral edema is associated with white matter changes in the splenium of the corpus callosum, an area previously implicated in the development of psychotic symptoms.³²

Multiple other pathophysiologic mechanisms underlying APEs were suggested. For example, Carbone et al explored psychological variables, proposing that personality traits and individual temperament may predispose athletes to misperceptions or influence the content and quality of their APEs.²⁶ Meanwhile, Popkin et al proposed that the APEs observed in dogsled racers may have reflected a delirium-like state.³⁶ In a more affectively driven account, Brugger et al suggested that transient limbic system hyperactivation, triggered by strong emotional states, could underlie hallucinatory experiences. They also posited that sensed-presence phenomena might serve a psychologically adaptive function, alleviating the distress of isolation during solo climbing. Additionally, they speculated that emotional stress and elevated endorphin levels could lower the seizure threshold in the temporal lobe, further predisposing individuals to perceptual anomalies.³⁰

Resolution and Recovery

All studies reported transient APEs that resolved with rest, within 1 or 2 d of cessation of the ultra-endurance sport. There were no documented long-term psychiatric outcomes or persisting impairments.

Discussion

Terminology

The terminology used across the included studies to describe APEs is highly variable, frequently imprecise, and lacking definitional justification. This inconsistency spans both clinical and descriptive language, with terms such as hallucination, illusion, misperception, psychosis, and delirium applied inconsistently and sometimes interchangeably. This lack of standardization complicates efforts to compare findings across studies, synthesize results meaningfully, or develop a coherent understanding of the underlying phenomena. Where attempts have been made to categorize the APEs using existing diagnostic constructs, including actual descriptions of the APEs taken from participants’ accounts would allow fellow researchers to better assess whether categories have been assigned correctly.

For example, the term visual hallucination has been used to describe both the perception of distorted stones²⁵ and the experience of falsely perceiving 2 flashlights moving in the darkness, interpreted as rescuers approaching.²⁹ These 2 accounts likely reflect very different perceptual mechanisms. The former could plausibly be explained by a normal perceptual experience—a headlamp beam bouncing off irregular surfaces and casting shadows in a tunnel. The latter, however, involves a more elaborate visual construction without an external stimulus imbued with meaning and emotional salience.

Such imprecision in terminology risks flattening the nuanced nature of the subjective experience. When rich phenomenological episodes are reduced to single clinical terms, especially without clear diagnostic framing, there is a risk of both overpathologizing adaptive or benign experiences and underrecognizing emerging psychopathology. For instance, using psychiatric language such as psychosis, without diagnostic context, may lead to inappropriate clinical conclusions. It also has the potential to introduce stigma, particularly when describing experiences in otherwise healthy individuals functioning at the limits of human endurance.

Contributing Factors

Hüfner et al described the “third-man phenomenon” as a specific symptom of high altitude psychosis.²³ However, “sensed presence” has been documented across a range of contexts that do not involve altitude.³⁸ Such cross-contextual occurrences highlight the importance of avoiding a siloed approach to conceptualizing APEs. Limiting explanations to discipline-specific causative factors, such as hypoxia in mountaineering, may inadvertently restrict theoretical development. If researchers broadened their scope to include the wider ultra-endurance athlete population, they may observe similar experiential phenomena occurring under markedly different environmental conditions. In illustration of this, the survey by Carbone et al revealed similar “sensed presence” phenomena in ultramarathon runners while not at altitude.²⁶

The consistent presence of sleep deprivation across nearly all included studies means that one must consider that ultra-endurance sport may act as a trigger for APEs primarily through the mechanism of extreme sleep loss. In other words, participation in prolonged events or expeditions may not inherently induce APEs; rather, it may be the inevitable sleep disruption that creates the conditions in which such experiences emerge. This view is supported by Waters et al, whose 2018 systematic review identified a clear association between APEs and sleep deprivation in all settings, not just ultra-endurance sport. They found that APEs typically appeared within 24 to 48 h of wakefulness, becoming increasingly complex and associated with disordered thinking at between 48 and 90 h.³⁹ This chronology closely mirrors the patterns reported in this review.

Carbone et al, whose study in high altitude ultramarathon runners was included in this review, further discussed the neurobiologic mechanisms that may underlie the link between sleep deprivation and APEs.²⁶ They drew on emerging theories of synaptic homeostasis, suggesting that prolonged wakefulness leads to increased synaptic potentiation without the corresponding downscaling that occurs during slow-wave sleep. This pruning process, essential for maintaining perceptual accuracy, is disrupted when sleep is curtailed. As a result, APEs may arise and persist.⁴⁰ Again, this is highly speculative but suggests a potential mechanism through which sleep deprivation could account for the emergence of APEs in ultra-endurance sport.

Implications

The findings of this review have important implications for the understanding of APEs outside of severe and enduring mental illness. From a scientific perspective, APEs in the context of ultra-endurance sport provide a unique window into how perceptual systems behave under multiple physical and environmental stressors. The limited evidence summarized in this review suggests that APEs may be an adaptive and predictable response, but a clearer understanding of when APEs remain benign and when they compromise judgment or situational awareness would be valuable when considering athlete safety and performance.

APEs during ultra-endurance sport are transient, context dependent, and self-limiting. However, without proper understanding of the environmental and physiologic stressors that elicit these phenomena, they may be miscategorized as signs of psychiatric pathology. This highlights the need for clinicians, particularly those working in sports medicine and rural and wilderness settings, to develop the ability to differentiate between benign exertion-related experiences and emerging psychopathology. Caution should be exercised before attributing such experiences to psychotic illness, especially in athletes without a prior psychiatric history.

For athletes, coaches, and event organizers, awareness and normalization of these phenomena may help mitigate distress and reduce stigma. Psychoeducation that frames APEs as potential by-products of extreme exertion and sleep deprivation could foster psychological preparedness and promote adaptive coping. In events where sensory deprivation, isolation, or prolonged wakefulness are expected, anticipatory guidance may assist athletes in interpreting these experiences constructively rather than fearfully.

Race organizers and expedition leaders may benefit from education in psychological resilience training and monitoring. The inclusion of mental status tracking during ultra-endurance events could reduce risk, particularly where altered perception may compromise safety (eg, navigation errors and moving in hazardous terrain). Although APEs do not, in most cases, indicate a need for an athlete to be withdrawn from competition, they should prompt careful consideration of potential risks. Accordingly, training of support teams could help to normalize APEs, reduce fear, and support psychological safety to minimize risk.

Researchers seeking to establish the prevalence of APEs, understand the conditions under which they occur, and identify implications for athlete safety and performance should aim to conduct prospective, mixed-methods studies with appropriate comparator groups. A framework for future research is outlined in Table 2.

Table 2.

Framework for Future Research to Improve Understanding of APEs in Ultra-Endurance Athletes.

Recommendation	Justification
1. Studies should be of prospective study design.	This should minimize the impact of recall bias and narrative framing influenced by cultural or personal meaning making.
2. Mixed methods and multiple measures should be employed.	Measurements could incorporate longitudinal symptom sampling, actigraphy-based sleep monitoring, environmental exposure tracking (eg, light, altitude, isolation), and post-event structured phenomenological interviews.
3. A consistent descriptive taxonomy should be used.	To improve validity and comparability, a consistent descriptive framework is needed to allow APEs to be characterized consistently across sporting disciplines. Our findings would suggest that this should be organized along at least 4 phenomenological dimensions: Sensory modality (eg, visual, auditory, somatic, multimodal); Complexity (ranging from simple distortions or misperceptions to complex, socially meaningful experiences such as “sensed presence”); Interpretative valence (neutral, comforting, or distressing); Functional impact (benign, performance enhancing, or safety compromising)
4. Qualitative data should be displayed alongside descriptive terms.	In addition to using a descriptive framework such as the one outlined above, quotations should be provided so that athletes’ first-person accounts may be examined alongside investigator-assigned categories to help develop consistent categorization between studies.
5. Studies investigating risk factors and causative mechanisms should include comparator groups.	The inclusion of matched non-competing control participants exposed to similar environmental conditions but without sustained exertion would strengthen causal inference, for example, race officials, checkpoint marshals, or support crew, who often experience comparable sleep deprivation, nocturnal exposure, isolation, and environmental stress yet are not subject to the same metabolic and physical load. Likewise, the comparison of athletes participating in events of similar duration and intensity but different environments or sporting disciplines also may help to disentangle the relative contributions of exertion vs hypoxia or other environment-specific factors.

APE, Anomalous perceptual experience.

Limitations

This systematic review has several limitations that must be acknowledged. First, the included studies were heterogeneous in design, quality, and methodology. They ranged from single case reports and small case series to field studies and cross-sectional surveys, each employing different instruments, outcome definitions, and levels of detail. Most studies lacked standardized or validated measures for APEs, and the absence of a consensus framework for describing these phenomena impedes accurate cross-study comparisons and risks conceptual ambiguity. This variability limits the ability to synthesize findings quantitatively or to draw generalizable conclusions.

Second, a substantial portion of the data derived from retrospective self-reports, personal narratives, or lay literature. These sources are inherently vulnerable to recall bias, misinterpretation, and narrative framing influenced by cultural or personal meaning making. In some cases, the experiences may have been embellished or selectively reported, especially where the APEs formed a salient or dramatic part of the athlete's story.

Third, the review is limited by language and publication bias. Only English-language peer-reviewed articles were included, potentially excluding relevant studies in other languages or gray literature sources.

Fourth, there is limited demographic diversity across studies. Most participants were male, often from Western or European contexts, and typically involved in mountaineering or ultramarathon running. This raises questions about the generalizability of findings to other genders, cultures, or ultra-endurance disciplines.

Finally, the absence of control groups or comparative designs precludes strong causal inference. Although sleep deprivation and altitude are frequently implicated, their relative contributions cannot be reliably disentangled without more rigorous experimental or longitudinal designs. Similarly, the decision to focus on ultra-endurance sport in this review may represent an overly narrow perspective because APEs occur in individuals without psychiatric illness in many nonsporting contexts such as the bereaved⁴¹ and spiritual believers.⁴²

Conclusion

This systematic review demonstrates that APEs are a recurrent and varied phenomena in the context of ultra-endurance sport. These experiences, which range from misperceptions to complex multimodal experiences, are most commonly visual but also may include auditory, somatic, and “sensed presence” phenomena. While traditionally associated with high altitude environments, similar phenomena were observed across a range of ultra-endurance disciplines, suggesting that these experiences are not exclusive to altitude-related pathophysiology. Sleep deprivation emerged as the most consistently reported contributing factor, with a clear temporal association between cumulative wakefulness and symptom onset. Other frequently implicated stressors included exhaustion and sensory and social deprivation. Although these phenomena are typically transient and self-limiting, they may have a variable impact—from neutral, to comforting, to distressing and performance impairing. Misinterpretation of such experiences, particularly by clinicians unfamiliar with ultra-endurance contexts or athletes concerned and fearful of their significance, may risk overpathologizing normal adaptive responses to extreme physiologic and environmental stress.

Given the limited number of high-quality studies and substantial methodologic heterogeneity, definitive conclusions about prevalence, etiology, and risk factors remain elusive. Future research should adopt a consistent taxonomy and use comparator groups to move beyond descriptive accounts and examine the mechanisms that contribute to APEs as well as their impact on athlete performance and safety.

Supplemental Material

sj-docx-1-wem-10.1177_10806032261423071 - Supplemental material for Anomalous Perceptual Experience During Ultra-Endurance Sport: A Systematic Review

Supplemental material, sj-docx-1-wem-10.1177_10806032261423071 for Anomalous Perceptual Experience During Ultra-Endurance Sport: A Systematic Review by Elizabeth E. Davidson, Sean L. Davidson and Paul Glue in Wilderness & Environmental Medicine

Footnotes

Acknowledgments

The authors thank Christy Ballard, subject librarian (medicine, University of Otago) for providing assistance in formulating the database search.

ORCID iDs

Elizabeth E. Davidson

Sean L. Davidson

Ethical Considerations

There are no human participants in this article, and informed consent is not required.

Author Contribution(s)

Elizabeth E. Davidson: Conceptualization; Formal analysis; Methodology; Writing – review & editing.

Sean L. Davidson: Conceptualization; Formal analysis; Methodology; Writing – review & editing.

Paul Glue: Project administration; Supervision; Writing – review & editing.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Previous Presentation

Presented at the Royal Australian and New Zealand College of Psychiatrists (RANZCP) 2025 New Zealand Conference, September 8–10, 2025, Dunedin, NZ.

Supplemental Material

Supplementary material associated with this article can be found in the online version at .

References

Eliot

. The Waste Land. Graphic Arts Books; 2021.

Zaryski

Smith

. Training principles and issues for ultra-endurance athletes. Curr Sports Med Rep. 2005;4(3):165-170.

Puce

Ceylan

Hİ

Trompetto

, Cotellessa F, Schenone C, Marinelli L, et al.

Optimizing athletic performance through advanced nutrition strategies: can AI and digital platforms have a role in ultraendurance sports?

Biol Sport. 2024;41(4):305-313.

Henderson

. Move over, marathons: the ultra-endurance sports that are redefining fitness. The Guardian. March 22, 2024. https://www.theguardian.com/lifeandstyle/2024/mar/22/ultra-endurance-sports-long-distance-running-skiing-swimming

Bell

Halligan

Ellis

. The Cardiff Anomalous Perceptions Scale (CAPS): a new validated measure of anomalous perceptual experience. Schizophr Bull. 2006;32(2):366-377.

Taylor

Vaidya

. Descriptive Psychopathology. Cambridge University Press; 2008, https://doi.org/10.1017/cbo9780511552106

Kwapil

Kemp

Mielock

, Sperry SH, Chun CA, Gross GM, et al. Association of multidimensional schizotypy with psychotic-like experiences, affect, and social functioning in daily life: comparable findings across samples and schizotypy measures. J Abnorm Psychol. 2020;129(5):492-504.

Wright

Fowler

Greenwood

. Developing a dynamic model of anomalous experiences and function in young people with or without psychosis: a cross-sectional and longitudinal study protocol. BMJ Open. 2018;8(11):e022546.

van Os

Linscott

Myin-Germeys

Delespaul

Krabbendam

. A systematic review and meta-analysis of the psychosis continuum: evidence for a psychosis proneness-persistence-impairment model of psychotic disorder. Psychol Med. 2009;39(2):179-195.

10.

Krasnov

Lebedev

West

. Psychiatric problems arising in extreme environmental circumstances. In: Henn F, Sartorius N, Helmchen H, Lauter H, eds. Contemporary Psychiatry. Springer; 2001:pp.1007-1013. https://doi.org/10.1007/978-3-642-59519-6_58

11.

Reeve

Sheaves

Freeman

. The role of sleep dysfunction in the occurrence of delusions and hallucinations: a systematic review. Clin Psychol Rev. 2015;42:96-115.

12.

Shackleton

. South: The Endurance Expedition. Penguin Books; 2015.

13.

. Chan S. The strange and intriguing world of running hallucinations. Runner’s World. February 17, 2022. Accessed August 17, 2025. https://www.runnersworld.com/uk/training/motivation/a39119399/running-hallucinations/

14.

Mayer D. Ultrarunning hallucinations happen: Here’s how to deal with them. Trailrunner Magazine. January 25, 2017. Accessed December 8, 2025. https://www.trailrunnermag.com/training/trail-tips-training/ultrarunning-hallucinations/

15.

Anon. Share your hallucination stories. Reddit Forum. N.d. Accessed December 8, 2025. https://www.reddit.com/r/Ultramarathon/comments/1fibd77/share_your_hallucination_stories/

16.

Hüfner

Falla

Brugger

, Gatterer H, Strapazon G, Tomazin I, et al.

Isolated high altitude psychosis, delirium at high altitude, and high altitude cerebral edema: are these diagnoses valid?

Front Psychiatry. 2023;14:1221047.

17.

Suedfeld

Geiger

. The sensed presence as a coping resource in extreme environments. In: JH

Ellens

, ed. Miracles: God, Science, and Psychology in the Paranormal: Parapsychological Perspectives. Praeger; 2008:pp.1-15.

18.

Page

McKenzie

Bossuyt

, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ. 2021;372:n71.

19.

Ouzzani

Hammady

Fedorowicz

Elmagarmid

. Rayyan—a web and mobile app for systematic reviews. Syst Rev. 2016;5(1):210.

20.

Moola

Munn

Tufanaru

Aromataris

Sears

Sfetcu

, et al. Systematic reviews of etiology and risk. In: Aromataris E, Munn Z, eds. JBI Manual for Evidence Synthesis. JBI; 2017:Chap. 7, pp. 267. https://doi.org/10.46658/jbimes-20-08

21.

Munn

Barker

Moola

, Tufanaru C, Stern C, McArthur A, et al. Methodological quality of case series studies: an introduction to the JBI critical appraisal tool. JBI Evid Synth. 2020;18(10):2127-2133.

22.

National Institute of Health. Study Quality Assessment Tools. NIH; 2021. https://www.nhlbi.nih.gov/health-topics/study-quality-assessment-tools

23.

Hüfner

Caramazza

Stawinoga

, Nockler ERP, Fusar-Poli P, Bhandari SS, et al. Assessment of psychotic symptoms in individuals exposed to very high or extreme altitude: a field study. High Alt Med Biol. 2021;22(4):369-378.

24.

Kishi

Millet

Desplan

Lemarchand

Bouscaren

. Sleep and ultramarathon: exploring patterns, strategies, and repercussions of 1,154 mountain ultramarathons finishers. Sports Med Open. 2024;10(1):34.

25.

Huang

Chang

Kao

, Li LH, How CK, Wang SH, et al. Visual hallucinations in 246-km mountain ultra-marathoners: an observational study. Chin J Physiol. 2021;64(5):225-231.

26.

Carbone

Pagni

Maiello

, Tagliarini C, Pratali L, Pacciardi B, et al. Misperceptions and hallucinatory experiences in ultra-trailer, high-altitude runners. Riv Psichiatr. 2020;55(3):183-190.

27.

Firth

Bolay

. Transient high altitude neurological dysfunction: an origin in the temporoparietal cortex. High Alt Med Biol. 2004;5(1):71-75.

28.

Barnby

Bell

. The Sensed Presence Questionnaire (SenPQ): initial psychometric validation of a measure of the “sensed presence” experience. PeerJ. 2017;5:e3149.

29.

Garrido

Hüfner

. An episode of “third person” phenomenon involving somesthetic and visual hallucinations in a world-class extreme altitude climber. Wilderness Environ Med. 2023;34(4):549-552.

30.

Brugger

Regard

Landis

Oelz

. Hallucinatory experiences in extreme-altitude climbers. Neuropsychiatry Neuropsychol Behav Neurol. 1999;12(1):67-71.

31.

Windsor

. Voices in the air. BMJ. 2008;337:a2667.

32.

Hüfner

Brugger

Kuster

, Dunsser F, Stawinoga AE, Turner R, et al. Isolated psychosis during exposure to very high and extreme altitude—characterisation of a new medical entity. Psychol Med. 2018;48(11):1872-1879.

33.

Hurdiel

Monaca

Mauvieux

Mccauley

Van Dongen

Theunynck

. Field study of sleep and functional impairments in solo sailing races. Sleep Biol Rhythms. 2012;10(4):270-277.

34.

Hurdiel

Pezé

Daugherty

, Girard J, Poussel M, Poletti L, et al. Combined effects of sleep deprivation and strenuous exercise on cognitive performances during the North Face® Ultra Trail du Mont Blanc® (UTMB®). J Sports Sci. 2015;33(7):670-674.

35.

Hoffman

Longobardi

Burt

Nardi

. GPS tracker-enabled rescue of a lost runner during a wilderness ultramarathon: a case report. Curr Sports Med Rep. 2018;17(10):332-334.

36.

Popkin

Stillner

Pierce

. Organic mental disorder associated with prolonged competitive stress. Compr Psychiatry. 1981;22(5):522-527.

37.

Lund

. Marathon volleyball: changes after 61 h play. Br J Sports Med. 1985;19(4):228-229.

38.

Barnby

Park

Baxter

Rosen

Brugger

Alderson-Day

. The felt-presence experience: from cognition to the clinic. Lancet Psychiatry. 2023;10(5):352-362.

39.

Waters

Chiu

Atkinson

Blom

. Severe sleep deprivation causes hallucinations and a gradual progression toward psychosis with increasing time awake. Front Psychiatry. 2018;9:303.

40.

Bersani

Iannitelli

Pacitti

Bersani

. Sleep and biorhythm disturbances in schizophrenia, mood and anxiety disorders: a review. Riv Psichiatr. 2012;47(5):365-375.

41.

Sabucedo

Evans

Hayes

. Perceiving those who are gone: cultural research on post-bereavement perception or hallucination of the deceased. Transcult Psychiatry. 2023;60(6):879-890.

42.

Lifshitz

van Elk

Luhrmann

. Absorption and spiritual experience: a review of evidence and potential mechanisms. Conscious Cogn. 2019;73:102760.

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

1.20 MB