How bad is kickboxing for your brain?

Question

I'm not asking for medical advice, I'm just asking this out of sheer curiosity:

To me it seems that kickboxing is the best kind of workout I could get, nothing else gets me in shape quite as quickly and as well. But as a noncompetitive kickboxer, I've always wondered what doctors would say about the potential for brain damage with kickboxing.

I mean, is it something that always occurs, or is it incidental? Sometimes when I'm hit well (about 2 - 3 times every training), I see stars and feel a little lightheaded. I've always wondered what's actually going on in my body when that happens. I mean, most sports tend to damage you a little, but in the long run the gains are worth it and you heal from the damage. Or is the damage you do to yourself with kickboxing beyond healing (and if so, is there a point of no return)?

Answer 1

I don't think the science is settled to a degree where we can give a solid answer, or make too many specific conclusions. Disclaimer: I'm not a kickboxer, and I haven't studied the subject deeply.

Dementia pugilistica

Getting hit in the head is not good for your brain. Getting hit a lot in the head is very bad for your brain. That's true regardless of dosage, but large, repeated doses of getting hit in the head over long periods of time are particularly problematic.

Medicine has known about the brain damage from boxing and kickboxing for a long time. We have a name for it:

Dementia pugilistica...[is a] variant of chronic traumatic encephalopathy... Symptoms and signs of [dementia pugilistica] develop progressively over a long latent period sometimes amounting to decades, with the average time of onset being about 12 to 16 years after the start of a career in boxing. The condition is thought to affect around 15% to 20% of professional boxers.

I would argue that there are probably a lot of people with minor brain damage that doesn't rise to the level of dementia pugilistica. That damage might be insignificant, but it exists. This is backed up by more recent studies, as reported in the LA Times:

A yearlong study of boxers' and mixed martial-arts fighters' brain activity has found those who fight for more than six years begin to experience damage and those who fight longer than 12 years expose themselves to an even greater decline each time they return to the ring.

Mitigation

The degree of brain damage depends greatly on how you train. Competing seriously is definitely a different animal from training hard, and training hard is different again from training casually. Getting your bell rung is a minor concussion, make no mistake, and those are no good. But in terms of serious damage, I bet a lot of people get a handful of minor concussions spread out over a few years of training and don't suffer any major brain damage. Taking three or four ring fights a year, and the training that requires, would probably mean a greater degree of brain damage. (Not debilitating in every case by any means, but it's certainly present.) Doing this for several years would in most cases cause noticeable problems.

Reading up on the signs of concussions is extremely informative. Staying out of hard training after a serious or moderate concussion is definitely a good idea. It would be a good idea for boxing and kickboxing coaches (in addition to grappling and field sports coaches) to adopt a concussion-recognition protocol. The King-Devick test has been shown to work well for boxing and MMA:

The King-Devick (K-D) test is based on measurement of the speed of rapid number naming (reading aloud single-digit numbers from 3 test cards), and captures impairment of eye movements, attention, language, and other correlates of suboptimal brain function. We investigated the K-D test as a potential rapid sideline screening for concussion in a cohort of boxers and mixed martial arts fighters.

In particular, getting knocked out or losing the match were predictors of damage:

Those with loss of consciousness showed the greatest worsening from prefight to postfight. Worse postfight K-D scores and greater worsening of scores correlated well with postfight MACE scores.

So work on your slipping and defense!

It is also probably a good idea to get regular MRIs or other brain tests done, if you continue to train over several years. As noted in the LA Times article, this is already enforced by boxing commissions.

But in the end, hard training is not knitting class. The risks of learning to hit and get hit can be mitigated through careful control in sparring and diligent use of equipment (and recognizing the limitations thereof), but at some point you're going to get concussed.

Answer 2

The biggest risk with concussions is getting a second one shortly after the first. For competetive boxers and kickboxers, this means the 10 count and standing 8 count are sentencing them to long term brain damage. If you're training casually, wearing very good headgear (Winning FG-2900 if you can afford it, Rival d3o would seem to be a good second choice) and a very good mouthguard (custom made for boxing) will help. Also, if you get hit once and see stars - call your sparring off right away, and don't finish the round. You'd want to not do any further sparring for at least 2 weeks.

Answer 3

What is a concussion?

In the last few years we've gotten a lot more info on them, and literally, they are brain damage. What makes them especially dangerous is that concussions can be extremely unpredictable in terms of cause to effect - sure, getting hit harder in the head is worse, but sometimes lighter hits can cause severe concussions or heavier hits not one at all.

Concussions build up over your lifetime. Earlier concussions make later ones worse and more damaging. Receiving a second concussion while still under the effects of a first one can literally kill you. (High school football deaths are mostly from this.)

The only way to avoid concussions is don't hit your head at all.

That said, you can do a few things if you're going to be in an activity where these happen.

1. Wear headgear, use gloves. Preferably, go light. Really preferably, don't hit each other in the head and train well to take falls. Obviously, this runs counter to a lot of self defense training and sports, so you have to figure out where on the scale you want to be and how many head shots and how hard is going to be necessary for you to develop and keep your skills and conditioning.

2. Strengthen your neck muscles. The stronger your neck, the better you can take those shots because you'll have better stabilizer muscles. You can still roll with punches, you just don't want the whiplash effect happening. Stats show sports you wouldn't necessarily think of as being that brutal to the head having high rates of concussions (soccer, volleyball), primarily because they don't do a lot of strength training for the neck and supporting muscles.

3. Learn what the signs of a concussion are. Don't ignore them. Don't try to tough it out.

When do you have a concussion?

The old way of recognizing a concussion was to ask people things like - "How many fingers am I holding up?" "Who is the President?" "What is your name?" These are valid in the loosest sense - if you lose the ability to visually focus, if you cannot remember things (including short term memory loss - "What were you doing 2 minutes ago?"), you have a concussion.

Do you have a headache? Do you feel nauseous? Do you feel dizzy? Does light seem too bright? Do you slur your speech or mix up your words? You also have a concussion.

If someone's eyes look in different directions, or the pupils do not match in size, there is a concussion. If you shine a light in their eyes and they don't react, there's a concussion.

Sports teams now have a computerized word test they run people through while they're healthy and after they take a hit, run them through again - if they drop below a certain performance level, this indicates a concussion as well.

What do you do if you have a concussion?

If you have a headache that seems to be getting worse? Go to the hospital RIGHT AWAY. The worst case scenario is internal brain swelling/bleeding. People who die from concussions typically die 30 minutes to a few hours after taking the hit, as their brain slowly swells and crushes itself inside their skull.

If not, the answer is it's time for you to stop training. Take a rest. Go home.

Now comes the other unfun part of recovering from a concussion. You're looking at 3-10 days of recovery IF you rest. Rest means:

1. Don't take any other head hits
2. Try to engage your brain as little as possible - no reading, no studying, no figuring out the tough problem at work...

Non-rest can increase your concussion recovery time to months.

The concussion has damaged the neural connections in your brain, and you basically are stuck letting your brain connect things around again, starting from the most basic autonomic processes. Things like "pupils focus like this", "We control our tongue and mouth using these neural connections", etc. Trying to read or intake heavy information ends up causing the brain to prioritize high level processes and leaves the low level ones unrepaired.

Wow that sounds totally unreasonable!

Yep! The brain is not well designed to take hits. It helps if you remember that for most of human evolution we weren't designed to last quite as long as we do these days, nor did we need to do much more than organize hunting food or gathering it as a social group.

It's up to you to decide for your own health how much risks you want to take with head shots and how you want to train around that.

You can see a lot of traditional martial arts where sparring only involves body and leg shots. That's an adaptation, but not necessarily as good for self defense. You can also see arts where people do controlled drills most of the time, and only once in a while break out the head gear and go with any force. That's more useful. It really depends on what risks you plan on taking for you.

Just be aware - muscle heals easiest, bone heals ok, joints heal hard, the brain barely heals.

Answer 4

I also think it's worth mentioning that if you are a beginner then you should either, not be sparring until you learn proper technique, tactics, and defense, or spar with someone of your same level. Frankly, as a kickboxer, if you are sparring with someone who rings your bell two or three times each session, then you are sparring with someone who is too far beyond your level. It's one thing for your coach to toughen you up--that's part of the process--it's another thing for them to put you up with an opponent who is going to hurt you. Think about that and whether your coach is making good choices.

Answer 5

You should stop training IMMEDIATELY

I mean, is it something that always occurs, or is it incidental? Sometimes when I'm hit well (about 2 - 3 times every training), I see stars and feel a little lightheaded.

You are getting hit too hard too frequently. This is not normal or acceptable, neither for casual nor professional athletes. Also it is not necessary for your personal goals of getting fit.

Reconsider your training

You mention that kickboxing is great for getting you in shape fast. Bag and pads training sessions are great for this.

Sparring is not for 'getting fit' or athletic performance. It's seriously dangerous (if you're seeing stars). It's a testing ground for your technical skills and combat mentality - if you are interested in developing technical combat skills, you may try sparring again once you feel ready.

Sorry this is like 6 years late, but I hope some people in a similar situation read this. Stay safe!!!

Answer 6

Interesting question... just the other night there was a segment on brain injury on local TV ( not sure if you'd be able to see it or not... http://tvnz.co.nz/sunday-news/research-reveals-damage-football-video-4894963 )

basically it was saying that any concussion is BAD, but even more minor hits can cause injury.
It can the manifest itself in many ways later in life, like higher rates of depression.

Answer 7

How bad for your brain is Kickboxing and MMA?

TL;DR: Pretty bad, but not quite as risky as boxing.

From an article about an ongoing long-term study called the "Professional Fighters Brain Health Study", whose findings to date were published in 2015:

“Repetitive head trauma may be a risk factor for Alzheimer’s disease and is considered the primary cause of chronic traumatic encephalopathy (CTE),” wrote the authors in their new study. Alzheimer’s is a well-known form of dementia, while CTE is a progressive degenerative disease of the brain linked to memory loss, confusion, impaired judgment, impulse control problems, aggression, depression, and progressive dementia.

To understand how these sports might affect fighters’ brains, researchers from Cleveland Clinic turned to the data collected by the Professional Fighters Brain Health Study (PFBHS). They identified 224 professional fighters: 131 mixed martial arts (MMA) fighters and 93 boxers. The PFBHS athletes were all between the ages of 18 and 44 and the average time these professionals had fought was about four years, with an average number of 10 total matches. While slightly more than half had a high school education (give or take), just under half had spent at least some time in college. In terms of race, 89 were white, 59 black, and 76 other. Next, the researchers matched these athletes with 22 same-aged people with a similar level of education but no history of head trauma.

At the start of the study, all participants underwent an MRI scan to assess their brain volume and then they returned for a brain scan annually for four years after that. At each juncture, the researchers tested their verbal memory, processing speed, fine motor skills, and reaction times as a general assessment of brainpower. Next, the researchers calculated for each athlete a Fight Exposure Score, or FES, which combines duration and intensity of fight career.

Fighters with an FES score of four were found to be 8.8 percent slower in processing speed than those with an FES score of 0. Add to that, the higher the score, the smaller the brain volume, particularly in the thalamus and the caudate. The thalamus acts as a gateway to the cortex, the outer layer of brain tissue linked to consciousness and decision-making. The caudate resides in the basal ganglia, where it is part of a system responsible for voluntary movement. The researchers speculate the typical response to a punch — when a fighter’s head rotates slightly — might be the cause of volume loss in the thalamus and caudate.

More generally, smaller brain volumes plus higher Fight Exposure Scores were linked to slower brain processing speeds. In fact, the researchers estimated a 0.19 percent reduction in processing speed per fight and a 2.1 percent reduction for each increase in FES. Irrespective of age, boxers tended to fare worse than martial arts combatants.
- Head Blows And Brain Injury: Boxing And Mixed Martial Arts Cause A Similar Loss Of Processing Speed In Fighters' Brains

From another article about a second study, which borrowed some participants from the one linked above:

"While we already know that boxing and other combat sports are linked to brain damage, little is known about how this process develops and who may be on the path to developing CTE," study author Dr. Charles Bernick, a CTE researcher at the Cleveland Clinic said in an American Academy of Neurology written statement. CTE is only diagnosed through autopsy after death, but symptoms may be similar to Alzheimer's and include memory loss, aggression and difficulty thinking.

For Bernick's study, which will be presented at the academy's annual meeting in New Orleans next week, researchers looked at 78 boxers and mixed martial arts (MMA) fighters, average age of 29, who were enrolled in the ongoing "Professional Fighters Brain Health Study." The fighters underwent MRI brain scans and also took computer tests to measure their memory and thinking abilities, and were then split into groups based on whether they had more than or less than nine years of fighting experience.

The researchers found in both groups that those with more years of fighting experience overall, as well as those participating in more fights per year, were more likely to have lower brain volumes than fighters who had the least experience. In those with fewer than nine years experience, there was no link between fighting and symptoms of memory loss or cognitive decline. But among fighters with more than nine years experience, those who fought the most times annually performed worse on thinking and memory tests.
- Boxing, MMA study examines threshold before fighters suffer brain damage

From the abstract for a report titled "Kickboxing sport as a new cause of traumatic brain injury-mediated hypopituitarism" published in the Oxford Journal of Clinical Endocrinology in 2007:

OBJECTIVE:
Traumatic brain injury, which is a frequent and a worldwide important public health problem, may result in pituitary dysfunction. Concussion, a common type of lesion after traumatic brain injury, is an injury associated with sports including boxing and kickboxing.... Head is the most common site of injury in amateur and professional kickboxers. Pituitary consequences of chronic repetitive head trauma in kickboxing have not been investigated until now. Therefore, the present study was designed to investigate the pituitary function in both retired and active amateur kickboxers.

PATIENTS AND DESIGN:
Twenty-two amateur kickboxers who have boxed in national and international championships (16 men, 6 women) with a mean age of 27.3 +/- 7.1 years, and 22 age- and sex-matched healthy controls were included in the study. Basal hormone levels were obtained from the participants. To assess GH-IGF-I axis, GHRH + GHRP-6 test and glucagon stimulation tests were used. Hypothalamo-pituitary-adrenal axis was assessed by glucagon stimulation test.

RESULTS:
When mean basal hormone levels were compared between kickboxers and the controls, IGF-I level was significantly lower in kickboxers (P < 0.05). Five (22.7%) and two (9.1%) of the 22 kickboxers had GH deficiency had ACTH deficiency, respectively. There were significant negative correlations between IGF-I levels and age, duration of sports and number of bouts (P < 0.05).

CONCLUSIONS: Present data clearly demonstrate for the first time that amateur kickboxing is a novel cause of hypopituitarism and kickboxers are at a risk for hypopituitarism especially isolated GH deficiency. Therefore, participants of the combative sports who were exposed to chronic repetitive head trauma need to be screened.

From an article on a 2014 study, limited to kickboxers and MMA fighters:

The rate of serious head injuries among professional mixed martial arts competitors is potentially twice that of professional football players, according to U.S. researchers.

The first event they looked for was knock-outs, in which players are literally knocked unconscious. The second, known as technical knockouts, occur when a referee or other authority judges that the player is too woozy to successfully defend him- or herself. Both kinds of knockout end the match.

The researchers also used statistics to investigate which factors were associated with a player having a higher risk of a knockout or a technical knockout due to being struck multiple times.

They found that players suffered a knockout in 12.7 percent of matches, and that a technical knockout took place in about 19 percent, meaning that nearly one-third of matches ended as a result of some type of head trauma.

These numbers mean that out of every 100 matches in which a mixed martial arts athlete could be knocked out, known as an athlete exposure, the injury would happen 6.4 times.

The comparable concussion rates for boxing and kickboxing are, respectively, 4.9 and 1.9 per 100 exposures, the authors note.

Moreover, they observed that competitors often used the few seconds before the referee stepped in to repeatedly kick the downed opponent in the head.

If all knockouts and technical knockouts are counted as concussions, the rate among professional mixed martial arts athletes seen in the study was about 16 per 100 athlete exposures.

It's tempting to compare those statistics to rates of concussions in sports such as football, which has been found to have 8.08 concussions per 100 plays, and ice hockey, with 2.2 concussions per 100 athlete-encounters.
- Head injury risk is high in mixed martial arts: study

Conclusion:

Like any sport in which the head is being struck, kickboxing and MMA carry high risks of brain injury. We don't have a lot of reliable statistics that might help us quantify the risk, but all the data we do have says that yes, kickboxing and MMA clearly cause brain damage in many of the people who participate in them.

The reasons for having relatively little data on kickboxing and MMA (compared to the much larger amount of data on other sports, like boxing and football) is pretty easy to explain: Professional kickboxing and MMA haven't been around for very long, they are still in the process of developing regulatory standards in many countries, and there aren't many professionals in these sports. MMA, for example, began in the 90's; professional boxing has existed for centuries. MMA was virtually unregulated almost everywhere until the 2000's and it is still unregulated in many countries; professional boxing has been subject to the Marquess of Queensberry Rules (and later regulations based on Queensberry) since the 1860's. An informal effort conducted by Sherdog.com estimated that there are roughly 5,000 active MMA fighters in the world right now (the largest MMA organization, the UFC, has only 600 fighters on its roster); Boxrec lists about 22,000 pro boxers who have fought at least once in the past year, and it is safe to assume that they missed a good number of boxers, so the real number is probably closer to 30,000.

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Why is Kickboxing bad for your brain?

TL;DR: Because you're getting hit in the head.

American football is considered the "most concussive sport", but that's only because we don't track concussions in combat sports.

“[Boxing] is not really tracked the way school sports are tracked,” says Robert Cantu, clinical professor of neurology and neurosurgery at the Boston University school of medicine. “Concussions in boxing are a poorly reported sample, but at B.U. we’ve had a 100% incidence of CTE ["chronic traumatic encephalopathy", a degenerative neurological condition caused by repeated blows to the head] in the boxers we’ve studied¹.”

With good reason. Various studies have put the force delivered by a blow from a trained boxer at anywhere from 450 lbs. (204 kg) to over 1,400 lbs. (635 kg), enough to accelerate the head to 53 g’s. Those forces hit in one of two ways - linear and rotational - and neither of them is good.

“Acceleration from a straight-on punch is linear, while a roundhouse is more rotational,” says Dr. Christopher Giza, professor of pediatric neurology and neurosurgery at UCLA’s Mattel Children’s Hospital, and a former commissioner of the California State Athletic Association. “We think rotational forces are more important in getting knocked out, but most punches have components of both.”

Within the brain, it’s the white matter - or the fatty sheathing on nerve cells that serves as insulation and connective tissue - that suffers the most. “The brain has the consistency of firm Jell-O,” says Giza. “If you shake or twist it you put strain on the connections, leading to stretching or tearing.” That causes both immediate and long-term harm, with the damaged connective tissue leaking what are known as tau proteins, which build up over time to form the signature deposits that signal CTE.

The brain’s slightly loose fit in the skull causes other problems. A thin layer of fluid surrounding the brain is supposed to provides shock absorption in the case of minor blows, but when you get hit hard enough, that little bit of wiggle room allows the brain to rattle around, with soft tissue colliding with unyielding bone. That can cause shock, bruising and even bleeding and death.
- Pacquiao, Mayweather, and the Physics of Getting Punched in the Head

Neurologist Dr. Margaret Goodman, former Chair of the Nevada State Athletic Commission's Medical Advisory Board, says that sparring is a particular cause for concern:

When a fighter is licensed to compete - whether it is for one bout or the entire calendar year, it is a green light for them to spar. Sparring means head shots and further exposure to brain damage. No fighter should receive a boxing license unless they prove they are fit to spar.
- Jones-Hopkins: The Worst Side of Boxing

And:

"Irrespective of the fighter’s age,” Dr. Goodman continued, “there are really extensive tests that need to be done based on somebody’s MRI studies, neuropsychological testing, neuropsychological exams... I still see fighters that I have concerns about, not just in boxing but also in MMA. Some of these athletes that have continued to compete year after year after having so many knockout losses that it takes a great deal of effort."
- Dr. Margaret Goodman on Fighter Safety and PEDs in Boxing: Part One

And:

"I completely agree with Roy [Jones Jr., the boxer] that balance problems are one of the earliest signs of brain damage from boxing. I think it is admirable that he is seeking treatment. There are certain types of physical therapists that also specialize in balance retraining, and it can be successful - to some degree. With that said, the only sure way to improve balance caused by chronic brain injury from boxing is to stop getting hit in the head. Roy has been one of the greatest boxers of our time. He is brave enough to admit he has neurological problems from boxing. Continuing to spar and fight will significantly worsen these problems and contribute to other more serious problems, like cognitive dysfunction (disruption in memory/concentration) in the future. I believe that his balance issue is a significant warning that needs to be heeded. You cannot spar away age or neurological problems irrespective of any medical therapy."
- Dr. Margaret Goodman Speaks Out About Roy Jones

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Will brain damage from kickboxing get better over time?

TL; DR: No. Some symptoms might improve slightly if you stop getting hit, but damage from repeated traumatic brain injuries is basically irreversible and permanent.

Brain traumas, especially chronic injuries such as those sustained in sports can, over time, lead to irreversible brain damage. There is just so much jarring and shaking the brain can take. The difficulty is that the most serious, long-term symptoms often don't show up until later in life, but clearly CTE can develop almost any age...

Chronic traumatic encephalopathy affects many areas of a person’s functioning, including mood, emotional regulation, cognitive capacity, memory, and personality. It often doesn’t develop for years after the traumas occurred, and can present with a different constellation of symptoms in each person it affects...

Its prevalence in boxers continues. One recent review study of athletes who were diagnosed with CTE found that of the 51 confirmed cases of CTE, 46 were in athletes – and of these, 39 were boxers. Five football players, a soccer player, and a wrestler made up the remainder of the athletes affected by chronic brain trauma.

When the head undergoes a trauma, the brain takes a hit. Brain tissue may be insulated by layers of bone and fluid, but severe or repeated injuries disrupt the neural communication in the brain. Recent research on the long-term effects of concussion offers a picture of the lasting effects a brain injury can have. Lateral, or side-to-side, traumas are more damaging to than sagittal, or front-to-back, motion...

The brain trauma associated with CTE may also trigger the death of neurons; inflammation in the brain; and damage to the white matter, the connective fibers in the brain by which neurons “talk” to one another. One team of CTE researchers suggests that there are probably many “pathological cascades” that are occurring over time. These cascades are thought to continue throughout the course of a lifetime. And the worse the initial injury – or injuries – the more severe the brain damage that can follow.

There are likely multiple mechanisms by which traumas can lead to brain damage and dementia, and the more traumatic and more repetitive they are, the more likely they are to result in irreversible damage.
- Athletes and Brain Trauma

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Fatalities in Boxing and MMA:

I did some research, and found that over a period of about 7 years, the rates of deaths from injuries sustained in the ring were roughly similar between professional boxing and regulated/sanctioned MMA contests:

Recorded MMA deaths in regulated fights:

1. Sam Vasquez 30 Nov. 2007
2. Michael Kirkham 28 Jun. 2010
3. Tyrone Mims 11 Aug. 2012
4. Booto Guylain 5 Mar. 2014

Pro boxing deaths in regulated fights during that same period:

1. Yo-sam Choi 25 Dec. 2007
2. Alex Aroy 4 Feb. 2008
3. Rafael Ortiz 8 Mar. 2008
4. Hi Cho (Mikeo Takeuchi) 3 May 2008
5. Samora Msophi 27 Jun. 2008
6. Luis "Tino" Lugo Quintero 27 Jun. 2008
7. Dachirri "Bashiru" Thompson 27 Jul. 2008
8. Daniel Aguillon 15 Oct. 2008
9. Benjamin "El Michoachano" Flores 30 Apr. 2009
10. Marco Nazareth 18 Jul. 2009
11. Francisco "Pancho" Moncivais 24 Jul. 2009
12. Somboon Wiengchai 12 Oct. 2009
13. Francisco "Paco" Rodriguez 20 Nov. 2009
14. Hirokazu Yamaki 19 Feb. 2010
15. Ki suk Bae 17 Jul. 2010
16. Anele Makhwelo 7 Oct. 2011
17. Roman Simakov 5 Dec. 2011
18. Karlo Maquinto 28 Jan. 2012
19. Muhammad Afrizal 30 Mar. 2012
20. Jose Angel "Vitaminas" Jimenez 31 Mar. 2012
21. Willman Rodriguez Gomez 4 May 2012
22. Ermelito "Jog" Alim Jr. 19 Jun. 2012
23. Okson Edison Ingamiua (Okson Palue) 21 Nov. 2012
24. Michael Norgrove 6 Apr. 2013
25. Francisco Javier "Frankie" Leal 19 Oct. 2013
26. Tesshin Okada 20 Dec. 2013
27. Oscar "Fantasma" Gonzalez 1 Feb. 2014

Methodology:

MMA:

I started with the "sanctioned bouts" section of the wiki article on fatalities in MMA, and did some googling to try to find records of other deaths in pro MMA bouts, which turned up nothing useful. I used the dates of the first and last deaths listed on the wiki page to limit my the data set - that is to say, I ignored all deaths before 30 Nov. 2007 and after 5 Mar. 2014. I also ignored all deaths that weren't caused by events that took place in the ring, and I ignored all deaths that resulted from unsanctioned/unregulated events.

Boxing:

I started with the raw data from the Manuel Velazquez Boxing Fatality Collection, and ignored all deaths due to sparring, practice, amateur bouts, and preexisting medical conditions. There were several deaths each related to amateur bouts and sparring, one related to training, and one related to a preexisting medical condition (a man who died shortly after a fight, but whose cause of death was kidney failure - from overuse of dietary supplements - and liver damage - from alcoholism). The Velazquez collection data didn't mention whether the bouts in question were regulated or sanctioned, so I had to assume that they were. However, I can't vouch for that, so my work might include some unsanctioned/unregulated fights.

Analysis:

There are probably at least 30,000 pro boxers in the world, vs. maybe 5,000 pro MMA fighters. That means that we should expect about 6 times more deaths in boxing, because 6 times more people box.

That is almost exactly what we see here. Four deaths in sanctioned MMA bouts, and twenty seven deaths in pro boxing matches. That's a ratio of 6.75:1. Since we expected 6:1 based on the differences in the number of people who participate in either sport, we only have to explain why it is 6.75:1 instead of 6:1.

I think the extra 0.75 deaths in boxing per death in MMA is probably just a problem with the resources available. The Manuel Velazquez Collection is a meticulously compiled, thorough, and rigorously updated resource so reliable that it is frequently used as the sole source of data for academic and medical journal articles about boxing mortalities. Thus, the data for boxing deaths is almost certainly complete, and includes every death that actually occured.

There is no comparable resource for deaths in MMA - I relied on Wikipedia and google. Thus, the data for MMA deaths may very well be incomplete.

Whether or not this is the case, the fact is that a difference this small, in a sample size this small, is probably not statistically significant.
- Quoted from my own work, originally posted by me in the Sherdog forums

Why is this relevant?

Because in every case, in both the MMA and Boxing fatalities, the cause of death was traumatic brain injury.

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¹"The 100% figure Cantu cites is derived, he readily acknowledges, from a self-selected population of fighters who come to his clinic seeking help for neurological symptoms. At least some of the larger population of boxers who don’t show up may be fine. What’s more, smart boxers - at least at the championship level - are increasingly taking steps to protect themselves, sparring less, engaging in safe aerobic training more and fighting perhaps only two bouts a year."