The research team, led by Emily Allen of Queen Mary University of London and Filippo Migliorini of University Hospital Halle, Martin Luther University Halle-Wittenberg, together with colleagues from institutions across Europe and Japan, distributed a study-specific questionnaire through judo clubs in the United Kingdom, Greece, and Japan. Twenty-three male coaches responded, with a mean age of 47.2 years, a range spanning 21 to 76 years, and a median coaching experience exceeding two decades. Seventeen of the 23 were based in the United Kingdom, with two from Greece, one from Japan, and three not specifying their location. The questionnaire was developed by a five-member expert panel combining judo and sports medicine expertise, including a 7th dan academic coach, a consultant sports physician, orthopaedic surgeons serving as national judo medical directors, and an elite athlete, and was pilot-tested with six coaches for usability before deployment.

The physiological story behind shime-waza-induced unconsciousness is well characterised in its acute phase. These techniques, of which the Kodokan Judo Institute recognises twelve, including the rear-naked choke known as hadaka-jime and the reverse cross strangle gyaku-juji-jime, apply compression to the neck using the arms, legs, or the uniform collar. The dominant mechanism is most plausibly transient cerebral hypoperfusion resulting from vascular neck compression, with carotid compression, impaired venous outflow, airway compromise, and reflex cardiovascular responses potentially contributing. Loss of consciousness has been reported to occur within ten to twenty seconds of effective strangulation, with recovery usually occurring shortly after release, although the authors caution that these timings vary by technique and circumstance. What remains genuinely uncertain, and what the study was designed to probe, is how coaches perceive the consequences of these episodes, particularly whether repeated exposure carries any longer-term neurological risk.

The survey results show that most coaches rarely witness these events. Nineteen of the 23 reported observing loss of consciousness less than once a month, and two said they had never seen it at all. Yet when it does occur, coaches recalled it far more often in competition than in training: fifteen of 23 pointed to the competitive setting, against just two for training. The authors suggest a plausible explanation rooted in the psychology of contest judo. Submission should prompt immediate release of a technique before unconsciousness sets in, but in competition, submitting ends the contest, and the willingness of a player to submit may be influenced by that stakes-laden context. The researchers are careful to stress, however, that these responses reflect how frequently coaches recalled observing loss of consciousness, not the relative occurrence of the event in either setting, since the questionnaire collected no exposure data such as coaching hours or numbers of players coached.

Perceptions of the technique most likely to cause unconsciousness were remarkably consistent: 21 of 23 coaches identified the collar-used type, in which the uniform collar is the principal means of applying compression, while none chose the arm-used type and only two chose the leg-used type. The authors note these descriptive labels are not a formal Kodokan classification and do not imply differential objective risk. Estimated durations of unconsciousness clustered at the short end of the scale: twelve of 22 respondents estimated less than ten seconds, nine of 22 estimated ten to thirty seconds, and only one estimated thirty seconds to a minute. Whether unconsciousness from a strangle carries consequences divided the cohort, with fifteen of 23 saying yes and seven saying no. Most telling of all, when asked whether such loss of consciousness could be similar to a concussion, eight said yes, nine said no, and six were unsure, a near-even split that the authors interpret as evidence of uncertainty and potential educational need rather than evidence that the event is either harmless or harmful.

This division matters because loss of consciousness from shime-waza and loss of consciousness from traumatic brain injury are not equivalent clinical entities. Acute unconsciousness after a strangle is generally associated with transient neck compression, whereas traumatic brain injury is caused by biomechanical forces from a throw, fall, or collision, can occur with or without unconsciousness, and carries established potential for longer-term neurological sequelae. The mechanisms, clinical context, and management pathways differ fundamentally. Critically, the evidence base for shime-waza remains insufficient to determine the long-term neurological consequences of repeated exposure, meaning an absence of demonstrated long-term harm should not be read as evidence of safety. The authors note that acute symptoms reported after recovery in young players have included transient confusion or disorientation, limb symptoms, and dizziness, with some symptoms not resolving immediately, reinforcing that any athlete who experiences unconsciousness requires appropriate assessment, observation, and a cautious return to play.

On the practical side, eighteen coaches, or 78.3 percent, reported awareness of a protocol implemented when an athlete loses consciousness from a strangle during competition. The authors are emphatic that awareness that a protocol exists does not confirm that a coach knows its content or applies it correctly. British Judo Association guidance, for reference, states that players must be removed from play immediately and are advised to rest briefly, although a graduated return-to-play is not always required. Perceptions of medical support also varied: fifteen of 23 believed there was adequate medical assistance and knowledge for dealing with unconsciousness after a strangle in competition, while seven disagreed. Notably, fifteen of 23 coaches reported noticing changes in their athletes’ behaviour as a result of being strangled, though the authors stress these are retrospective observations that cannot establish the presence, absence, severity, or duration of clinical symptoms.

The safety context the authors sketch is nuanced. Serious adverse events in supervised judo appear uncommon, and serious neurological complications reported within the sport are rare, with only one recorded case of carotid artery occlusion and right middle cerebral artery territory infarction. Reports of fatal neck restraint outside organised sport are not directly transferable to regulated training or competition, where supervision, rules, and prompt release of techniques meaningfully alter the context. Yet such reports illustrate the potential consequences of sustained or improperly applied neck compression. The authors also reference Katsu, or Kuatsu, the traditional Kodokan resuscitative practices associated with recovery after a choke, emphasising these are not an alternative to contemporary evidence-based medical assessment. Safe practice, they argue, depends on multiple safeguards operating together: technical instruction, precise execution and control of shime-waza, qualified supervision, ongoing education, and restrictions on use in younger age categories and in Veteran players aged sixty and above.

The study’s limitations are substantial and the authors confront them directly. The questionnaire was study-specific and non-validated, with no formal psychometric testing, no operational definition of loss of consciousness, and several items probing perceptions rather than objectively verifiable knowledge. The sample was small, predominantly United Kingdom-based, entirely male, and recruited through convenience sampling, so it cannot be interpreted as internationally representative. The English-only questionnaire may have restricted participation from Greece and Japan, and self-reported findings are susceptible to selection, recall, and interpretation bias. These constraints preclude any estimate of loss of consciousness incidence or any assessment of the quality or effectiveness of current safety practices. What the study does deliver is a map of where coach education may be useful, from recognition and assessment of unconsciousness to clearly defined escalation pathways, incident reporting, and medical access, and a call for prospective, exposure-based research using validated instruments, extending beyond coaches to examine the knowledge and attitudes of players themselves, and using video-based competition analysis to establish observed timing and frequency more reliably than retrospective recall ever can.

Subject of Research: Coaches' perceptions and self-reported practices concerning loss of consciousness from shime-waza strangling techniques in judo

Article Title: Loss of consciousness associated with Shime-Waza in judo: an exploratory study of coaches' perceptions, experiences, and practices

Article References: Allen, E., Singh, K., Blach, W., Ikumi, A., Sasaki, E., Illy, S., Angioi, M., Malliaropoulos, N., Migliorini, F., & Maffulli, N. (2026). Loss of consciousness associated with Shime-Waza in judo: an exploratory study of coaches' perceptions, experiences, and practices. Frontiers in Sports and Active Living, 8, Article 1955805. https://doi.org/10.3389/fspor.2026.1955805

Image Credits: AI Generated

DOI: 10.3389/fspor.2026.1955805

Keywords: judo, shime-waza, loss of consciousness, choking techniques, combat sports, coach education, concussion, sports medicine, injury prevention, questionnaire study, return to play, martial arts