Boxing - Is our brain on the ropes?
By Dr Thomas Di Virgilio (@ThomasDiVi), December 20th, 2020
Even if you are not a sports fan, you will have undoubtedly seen the famous photo of Muhammad Ali towering over a defeated Sonny Liston, or the clip where the same Ali dodges 21 of Michael Dokes’ punches in 10 seconds. In one form or another boxing has been part of human culture for millennia. Throughout the centuries this sport has evolved; rules have changed, equipment improved, training enhanced. However, one key aspect has essentially stayed the same: incapacitating the opponent before they incapacitate you.
Boxers are largely exposed to subconcussive head impacts (i.e. impacts that do not result in visible symptoms of concussion; soccer heading is also a prime example). There is still uncertainty surrounding repetitive subconcussive head impacts and the immediate/short-term changes that result in the brain, so more research is needed. Overall, there are growing concerns about the effects on brain health, and a need to better understand the factors (e.g., exposure to concussions/sub concussions; individual difference variables) that are at play.
Our research team has previously shown that 20 football headers affect how the brain talks to the muscles, so now we wanted to see if other sports found similar effects. Sparring sessions in boxing and other martial arts are well suited for research because they are often done as part of an athletes training regime, and are fairly easy to replicate in a controlled laboratory environment.
We recruited 20 boxers and Muay Thai athletes, and 20 healthy individuals as a control group. All participants completed baseline tests measuring communications between the brain and muscles in the lower limb and cognitive function. Participants in the experimental (sparring) group then completed a sparring session consisting of 3 x 3 minute rounds, replicating what they would do in a normal training session.
The results showed us that, similarly to soccer heading, a sparring session resulted in changes in the brain, and the brain-to-muscle pathways. More specifically, there was an increase in inhibitory mechanisms (i.e. a slowing down of the communications between brain and muscles) within the central nervous system. In order to function properly we need a good balance of excitation and inhibition in the brain, too much of one or the other can lead to health issues.
We also found that motor unit behaviour changes with subconcussion. A motor unit is made up by a neuron (main cell in the central nervous system) and all the muscle fibers it controls; the brain can perform virtually any task (from stitching up a cut artery to smashing a cement block with a big hammer) by changing the way motor units are activated.
Increased inhibition in the brain is seen following concussion and is thought to be a protective mechanism designed to help recovery. However, repeatedly activating this defensive response without any actual injury could create a toxic environment, ultimately damaging the brain. We have also said that a good balance of excitation and inhibition is needed in order to move properly; changes to this delicate balance in the brain may have knock on effects in other parts of the body. Therefore, it is interesting that we show changes in motor unit behaviour at the same time as increased inhibition. It is possible that the two are linked: increased inhibitory mechanisms in the brain change how the brain talks to the muscles. If the control the brain has over the muscle is not perfect, the athlete may be at greater risk of muscular injury. In fact, it is unsurprising that athletes returning to play following a concussion are more likely to sustain a musculoskeletal injury, suggesting the link between brain injury and increased likelihood of muscle injury are indeed related to these impaired brain-muscle communications.
Ultimately, more studies are needed as it is still unknown exactly how repetitive exposure to subconcussive impacts over the course of a game/season/career may negatively affect brain health. Furthermore, we believe the relationship between subconcussive head impacts and brain-to-muscle communications are particularly worthy of attention as it could link concussion/subconcussion to increased risk of other types of injury.
Our key papers can be found here:
https://www.thelancet.com/journals/ebiom/article/PIIS2352-3964(16)30490-X/fulltext
https://www.frontiersin.org/articles/10.3389/fnhum.2019.00294/full
Thomas Di Virgilio , PhD, is a Lecturer at the University of Stirling.
Image credit:
Photo of boxer by Ground Level Up Productions.
Motor unit image taken from Mosbys Medical Dictionary 8th Edition – ISBN 9780323052900