Being choked unconscious might not be good. But we have very little evidence that shows that it's bad to any significant degree, and considerable evidence that being choked all the way out doesn't seem to be of notable danger. Let's look at a few different kinds of evidence.
A side note: we must keep in mind the vast difference between being "choked out" to the point of tapping and being choked unconscious. We will not use the former interpretation. For us, "choked out" means choked past the point of losing consciousness.
Another side note: in medicine, choking and strangling are specific technical terms. We won't be using those more precise definitions.
Studies Where We Choked People Unconscious In a Lab
One obvious thing to do is choke someone unconscious while they're connected to a bunch of sensors, and see what happens.
There has been limited medical research regarding neck restraints. One of the first studies was conducted by the United States Military in 1943. A team of American military scientists examined the effect of acute cerebral anoxia —a short and severe lack of oxygen to the brain. To do this, they used an inflatable cervical pressure cuff designed to induce temporary arrest of circulation without affecting the respiratory tract; essentially, a mechanically created carotid pressure hold. The cuff was held down to the lower third of the neck and pressure increased to 600 mm of mercury within one-eighth second. One hundred and twenty six prison volunteers and 11 diagnosed schizophrenic patients were fitted with the cuff which was tightened until unconsciousness was induced. The average time from arrest of cerebral circulation to loss of consciousness was six to eight seconds. The study concluded that arrest of cerebral circulation in normal young men results in fixation of the eyes, tingling, constriction of the visual fields, loss of consciousness, and brief, mild tonic and clonic seizure after restoration of the blood flow. This study, though dated, is perhaps the largest study ever conducted in terms of the sheer number of participants. No deleterious effects were observed from repeated tests on these subjects.
Now, I'm not sure I trust these researchers. They're in the military, conducting tests on prisoners and mental patients. Perhaps their evaluation of deleterious effects is not, shall we say, the most thorough. So we have Ken Endow's DANGER IN THE JUDO CHOKE?, where they arrange an array of sensors to some guys and choke them out:
Is there any danger in the use of shimewaza? This is what a team of experts came together to try to discover. Representing several of Japan's foremost medical schools and universities as well as the Kodokan, this group of medical specialists and ranking educators used the electroencephalograph to detect brain changes; the earoxymeter for blood oxygen saturation, the sphygmomanometer for arterial blood pressure; the plethysmograph peripheral blood vessel reaction and the micropipometer for skin temperature changes. Other studies probed the plasma protein concentration, blood water volume, hematrocrit complete blood count, eosinophil count and urine 17 keto-steroid content.
After only 10 seconds of choking, the victims fell unconscious. As soon as they were diagnosed unconscious, the performer released them and, the subjects remained unconscious from 10 to 12 seconds. During this period the victims some times developed clonic, a jerking or fluttering, cramps. All subjects woke up spontaneously.
As the subject regained consciousness spontaneously his electroencephalogram readings returned to normal. It should be repeated that in all the cases the performer released his grip immediately after the subjects fell unconscious, thereby limiting the effect of choking to a short period. But had the strangulation continued serious aftereffects would have been expected.
The electroencephalograph recorded symptoms very similar to that of a short epileptic seizure.
Those findings sound alarming but not actually dangerous or troubling.
We also have this three-way comparison between judoka (who choke and get choked regularly, though not normally to unconsciousness), boxers (who punch and get punched in the head regularly), and a non-choking, non-punching control group. It's pretty straightforward what they found:
Long-term effects of boxing and judo-choking techniques on brain function.
Author: Rodriguez G , Vitali P , Nobili F
Source: Italian Journal of Neurological Science, 19(6): 367-72 1998
This study shows the relevance of the neurophysiological assessment of athletes engaged in violent sports which can cause brain impairment. In fact, while professional boxers may show brain functional impairment in comparison to normal subjects, judoka do not.
So we see that normal judo practice, which might involve the occasional choke-out, has no evidence of being injurious to brain function in the long term. This is supported by another study where they choked some guys unconscious and looked at their brain waves. Again, the results are not a cause for worry:
Spectral analysis of electroencephalography changes after choking in judo (juji-jime).
Author: Rau R , Raschka C , Brunner K , Banzer W
Source: Med Science Sports Exercise, 30(9): 1356-62 1998
RESULTS: A significant increase of global field power in the delta- and theta-range occurred, while physiological alpha-power decreased. These changes in the low-frequency range reached a statistically significant level within a time span up to 20 s after choking, which was performed at an average choking time of 8 s. In no case did choking provoke neuropsychological symptoms. Yet, spectral EEG-analysis revealed subclinical changes of brain function.
CONCLUSIONS: Choking in judo may induce subclinical electroencephalographic perturbations. The extent and duration can be objectified by means of spectral analysis of EEG data, global field power computation, and brain-mapping representation.
Let me reiterate the non-troublesome aspects of their results: these changes in brain function were neither brain damage nor injury, and the results were less than what a doctor would consider problematic.
Weighing this kind of evidence, the Kodokan issued two warnings, the first of which has good evidence, the second of which seems a reasonable precaution:
To prevent any dangers that may accompany the choke, the Kodokan bulletin advises it is dangerous to perform the choking [both] on subjects with cardiac disorders or those suffering from hypertension since the load to the heart and the rise in blood pressure is marked. It is also advised that it is dangerous for youngsters whose nervous system and heart have not yet attained complete development.
(Source: Ken Endow, DANGER IN THE JUDO CHOKE?) You can see details here in an awful pseudo-PDF format.
Epidemiological-Type Evidence Where We Check How People Turned Out After They Get Choked Out In Training and Competition
If being choked out was known to produce injuries or deaths in training or competition, that sure would be a sign that we shouldn't do it. Yet, judo organizations keep good records, and we find the opposite. A judoka-doctor argues persuasively from empirical evidence that choking someone unconscious in the manner of judo, Brazilian jiu-jitsu or modern no-gi grappling is reasonably safe:
[Choking in judo] is considerably less dangerous than a "knock-out" in boxing and there is no necessity of completely excluding "choking" from Judo, provided necessary precautions are taken.
There are, however, three main dangers of choking based upon the above experiments.
- To perform a "choking" hold on subjects with cardiac disorders or hypertension.
- To apply "choking" on youngsters whose central nervous system and heart have not yet attained complete development.
- To continue to hold after the subject falls unconscious.
Since the advent of Judo, first developed by Professor Jigoro Kano in 1882, no death directly attributed to choking has been reported. There are four main reasons why fatalities do not occur:
- Choking, whether in practice or competition is supervised and observed by qualified trained instructors and officials.
- The contestant submits before unconsciousness occurs.
- After choking the contestant regains consciousness naturally and spontaneously without difficulty in ten to twenty seconds.
- The immediate application of artificial respiration by the qualified instructor or official prevents prolonged hypoxia.
Choking in Judo is safe because since the advent of Judo statistics show no fatality attributed to the shime-waza. Moreover, scientific studies on choking reveal no deleterious after effects. Finally, the precautionary rules and methods used make the technique of choking a relatively safe means of subduing an opponent in competition.
(Source: E. K. Koiwai, M.D., How Safe is Choking in Judo?)
Our dear doctor goes further, investigating a number of deaths due to law enforcement choking various persons, and finds:
In all 14 cases, this author has noted evidence of injuries to the structures of the neck from bruises, ecchymosis, hemorrhages to fractures of the cartilage of the neck (Cases 1, 5, 10, 13, and 14), and intervertebral discs (Case 7).
He makes the point that these injuries suggest improper application of the choke, such that these should not be considered in the same category as actual judo techniques:
If the carotid artery hold is properly applied, unconsciousness occurs in approximately 10 seconds (8-14 seconds). After release, the subject regains consciousness spontaneously in 10-20 seconds. Neck pressure of 250 mm of Hg or 5 kg of rope tension is required to occlude carotid arteries. The amount of pressure to collapse the airway is six times greater.
(Source: E. K. Koiwai, M.D., Deaths Allegedly Caused by the Use of "Choke Holds" (Shime-Waza))
A Dissenting Case Report
Owens and Ghiadiali present a contradicting possibility. From the abstract:
A case is presented of a patient with signs of anoxic brain damage, with psychometric investigation showing memory disturbance consistent with a left temporal lobe lesion. This patient had been frequently strangled during his career as a judo player; it is suggested that such frequent strangulation was the cause of the damage. Such an observation indicates the need for caution in the use of such techniques.
I do not have access to the full text. It is not clear that judo is well implicated in this case, nor do we know the extent to which this individual was choked out (how often, how long, et cetera), nor can we extrapolate from this one data point. Even being charitable, the conclusion to take from this case would be "don't be choked all the way to unconsciousness, and if you do, don't do it frequently". NB: this is not shown, merely suggested as a cause for further research.
My Tentative Conclusion
There are some contraindications for being choked: heart conditions, hypertension, young kids. But people who are choked out for ten or thirty seconds seem to be fine within five minutes, and certainly by the next day. Being choked out repeatedly would seem to be a bad idea.
I'm not going to go out and try to get choked out. But if it happens in the course of training or competing, the only thing I'm worried about is that someone notices before too much time passes. Students should know to pay attention to their partner and not hold onto a choke with a limp partner. Instructors should pay attention to students who are grappling, taking particular note of those caught in a choke, and make sure nobody holds on to a choke after the other person passes out. These simple precautions have, according to the data, largely prevented choke-related serious injury in one of the world's most practiced martial arts.
Normal practice of grappling chokes is almost entirely safe. One instance of being choked out and immediately resuscitated doesn't appear to have any serious negative consequences, say both anecdotes and the data.
So barring contraindications, choke away, judoka.