The study found that brain volume loss in particular brain regions results in poorer brainpower. The researchers suggest this may relate to the way fighters receive head blows.
As well as shrinkage in parts of the brain, the fighters in the study suffered losses in brain processing speeds in comparison with controls who had never taken part in any type of sport that could lead to head injury.
The participants were all from a long-term cohort study - fighters tracked in the Professional Fighters Brain Health Study run by the Cleveland Clinic Lou Ruvo Center for Brain Health, in Las Vegas, NV.
The results, published online in the British Journal of Sports Medicine, show an average of 4 years of professional fighting across the athletes, who were between 18 and 44 years of age. They held professional fight licenses for combat sports, either boxing or mixed martial arts.
The number of professional fights they had taken part in ranged up to 101, with an average of 10 matches, and their professional fighting careers ranged up to 24 years.
At the start of the study, and annually for the next 4 years, all participants had:
- Brain volume assessed by magnetic resonance imaging (MRI)
- Brainpower assessed by tests of verbal memory, processing speed, fine motor skills and reaction times.
The researchers previously developed a way of scoring fighters' careers by duration and intensity of fighting - a "summary measure of cumulative traumatic exposure." Called the fight exposure score, or FES, it is a function of the total number of career matches and the average number of professional fights each year, producing a score of 0 to 4.
For the higher FES counts, the researchers found a reduction in brain volumes in particular regions, and a correlation with poorer cognitive performance.
An increased number of blows to the head, assumed from the more extensive fight histories, showed a correlation with lower volumes in the caudate and thalamus regions of the brain, which in turn were associated with lower processing speeds.
Some of the quantitative results of this were as follows. For each increase in fight exposure score (FES):
- There was a volume shrinkage of 0.8% in both brain structures
- A reduction in processing speed of 2.1%, which translated into an estimated 0.19% reduction per fight.
Fighters with an FES of 4 were 8.8% slower in processing speed than those with an FES of 0.
Cumulative brain damage
The thalamus of the brain acts as a gateway to the cortex and can affect a wide range of neurological functions, say the researchers. Dr. Charles Bernick, director of the Lou Ruvo Center and lead author of the study, explained that regional brain changes were an important measure of cumulative injury, and of worsening brainpower over time, even if changes are not noticeable from one day to the next.
Dr. Bernick told MNT: "The most common measurable relationship between smaller brain volumes and performance is in tasks that involve speed of processing information. Keep in mind, we are studying young active fighters, so the slower processing speed may be difficult for someone to notice on a day-to-day basis.
"However, the regions that show a correlation between fight exposure, volume and speed of processing are deep in the brain and receive input, connections, from a wide range of other areas that converge."
Dr. Bernick added:
"The importance of finding specific 'vulnerable' regions may allow us to track, at an individual level, change over time, and monitor accumulating injury."
Boxing 'more dangerous than martial arts'
Perhaps unsurprisingly, given their focus on the head, the boxers in the study generally fared worse than the martial arts combatants, irrespective of age. They showed smaller volumes in the scanned regions of the brain and gave slower mental performances.
If you want a combat sport that's less likely to cause brain damage, martial arts are better than boxing because they're not so focused on concussing the opponent.
"Perhaps the most obvious explanation is that boxers get hit in the head more," the authors suggest. "In addition to trying to concuss (i.e., knockout) their opponent, martial arts fighters can utilise other combat skills such as wrestling and jiu-jitsu to win their match by submission, without causing a concussion."
One of the explanations for the way in which the thalamus and caudate of the brain are particularly vulnerable to volume loss, the researchers say, is that punches delivered during a fight result, for example, in a rotational movement of the head.
Dr. Bernick is a supporter of the idea of monitoring sports fighters more closely and believes the fight exposure score provides a simple way of monitoring combatants' risks, directly linking an individual fighter's career with the potential effects on their brain as found in the research.
Asked by MNT if he believed there was enough interest in the industry for monitoring tools such as the FES to work effectively, he answered:
"Yes, I believe that athletic commissions that license fighters are very interested in tools that may help them in identifying athletes that may need closer scrutiny.
The information that goes into the FES is readily available public information and would be a simple instrument to institute."
Dr. Bernick added there was active interest for the idea in his home state of Nevada: "I will be presenting information about the fight exposure score to our state athletic commission at one of the upcoming meetings, as there is an interest in adopting it."
Fighters may be able to reduce their own risks
One part of some practical advice that fighters might take for their own protection can be interpreted as simply trying to win their matches and so, in the case of boxers, reduce how often they get a knockout (KO) or technical knockout (TKO).
But advice given by Dr. Bernick also applies to changes that fighters can make to their training and competition programs. He told MNT:
"From what we know of the relationship between exposure to head trauma and either imaging or performance on clinical testing, it seems most prudent to try and avoid significant head trauma in training (that is, limit the amount of hard sparring that is done in training), and allow enough rest time between competitions, particularly if it was a hard fight or if the fighter was KO'd or TKO'd."