Account for Variance in Concussion Tolerance Between Individuals: Comparing Head Accelerations Between Concussed and Physically Matched Control Subjects
Rowson S, Campolettano ET, Duma SM, Stemper B, Shah A, Harezlak J, Riggen L, Mihalik JP, Guskiewicz KM, Giza C, Brooks A, Cameron K, McAllister T, Broglio SP, McCrea M. Ann Biomed Eng. 2019 [Epub ahead of print]
Take Home Message
Prior to a concussion, football athletes experience more head impacts at higher magnitudes compared to non-concussed athletes with similar characteristics.
Investigators have reported a wide range of head acceleration during head impacts that cause a concussion. Further, investigators have reported that cumulative head impacts may also lead to a concussion. However, it is still unknown why some athletes suffer from cumulative or low magnitude head impacts and others do not. Therefore, the authors of this study examined the biomechanics of concussion in football when carefully selecting healthy controls for factors that may alter concussion tolerance. Athletes were selected from the Concussion Assessment, Research, and Education (CARE) Consortium cohort, which included 502 Division I collegiate football players from 4 universities and 2 military academies. These players had completed demographic reports and wore helmets equipped with head accelerometers between 2015 to 2017. Forty-four athletes that sustained a concussion were matched as closely as possible by body mass index, age, race and number of previous concussions. The authors focused on the time between the first day of practice and the date of a concussion for each matched set of players (concussed and healthy).
Athletes with a concussion experienced ~94 more head impacts and participated in ~4 more contact sessions compared to controls. Additionally, the athletes with a concussion suffered more severe contacts than controls. The authors performed a second analysis with just 24 of the best matched pairs. Among these 24 pairs of athletes, the athletes with a concussion had on average 205 more head impacts and greater head acceleration (~7g).
The authors reaffirmed that athletes with concussion experience greater head impact frequency and acceleration compared to their matched counterparts. They were also involved in more contact practices/games. The authors findings are novel because they tried to control for factors that may alter someone’s concussion tolerance; however, they had to make several large assumptions and may have missed other important factors (example: genetics). The author’s approach acknowledged that we may lack specific concussion head impact tolerances/thresholds because large cohorts hide the individual factors that increase risk such as physical traits. However, combining height and weight and matching by BMI may not be the best way to control and match for physical traits. For example, the physical attributes (muscle mass vs. adiposity) of an 18-year-old football player may not be the same as a 23-year player with the same BMI and concussion history. Additional efforts should be made to investigate other traits that may increase risk to poor head impact tolerance. Despite these limitations, this study reinforces the idea that clinicians should be aware that prior head impact may influence the chance of getting a concussion. Hence, we need to do more to encourage helmet-less practice drills and/or limiting the number of contact practices.
Questions for Discussion
Do you think these physical traits increase the risk of concussion? What additional factors do you think contribute to an athlete’s head impact tolerance?
Written by: Jane McDevitt
Reviewed by: Jeffrey Driban
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I think this is very interesting. It makes sense that those who received more head impacts suffer from more head related injuries. Their increased exposure to head contact makes it easier for them to come across a head injury. I think that controlling for outside factors the best they can worked well, however, I think it would be interesting to see if life stressors could have an impact of their head injury rate as well. Also, I wonder if we would find the same outcome in youth football.
I found this studies findings to be very interesting that it was not just an increase in g’s but also an increase in the number of head contacts. This study should be a good teaching tool that you don’t want your “best players” getting a lot of reps in practice, no matter how good they are, for it could cause them to be more likely to get a concussion due to the increase in the amount of impacts.
I think that a difference in neck strengths (as previous studies have shown) would also have an influence on the athlete’s head impact tolerance. I would be interested to see if that an increase in the number of impacts in ice hockey and soccer (due to heading the ball) would also cause a similar outcome.
Throughout my education I’ve learned that the brain is an organ floating in out cranium. I like to picture a pickle in a jar, if you move it it’s going to move. If you move it fast enough it will hit the jar. The pickle won’t necessarily be damaged by such a minimal impact, but if you keep shaking the jar for an entire season the pickle might look a little different. Every time the brain hits the skull, even if it’s minimal, will add up over time. This is increased by participating in sports. The fast movements and changing of direction is going to shake the brain, causing it to hit the skull more. I am interested to see how this concept varies sport by sport, and even compared to normal everyday life.
the anthropometric properties, maturity level, and skill of an athlete definitely have an effect on the risk of concussions. Both offensive and defensive players who are fast and strong have a relentless peruse for the desired play and a winning mentality will put their bodies on the line and do not hesitate to make dangerous plays sometimes. Tolerance to head impacts could be affected by cervical spine stability, strength, and mobility. The ability to absorb an impact through the kinetic chain and not just absorb it at the cranium can affect the tolerance to repetitive impact.
Reading this article I would have never guessed that body trait may or may not have a role in concussions. I do believe physical traits can increase the risk of concussions. I would assume that those with a lower BMI or lower body fat, muscle mass percentage would have an increased risk of a concussion due to decrease muscle mass and the inability for the neck musculature to properly absorbed the hit. Other times I believe that it’s just luck if the athletes aren’t expecting the hit, they cant anticipate it and tense up to absorb it. Depending on the tackle/hit there are some factors that contribute to an athlete’s head impact tolerance such as being tackled head down can cause a lot of damage regardless of head impact tolerance and things like neck strengthening exercises can build a tolerance. I feel that because a concussion is the brain hitting the skull, the idea that those who already have had a concussion previously are more prone to concussions as opposed to those who don’t. The brain is already injured it will most likely reinjure. I have seen a lot of concussions at my clinical site and it’s usually the same athletes because of their position they are more prone to head impact so maybe besides size weight and previous concussions, maybe the position of the athlete plays a role as well.