Cumulative head impact burden in high school football
Broglio SP, Eckner JT, Martini D, Sosnoff JJ, Kutcher JS, Randolph C. J Neurotrauma. 2011 Jul; ahead of print
Recent studies have been trying to look at how much force or how fast the head needs to be going to sustain a concussion (see past SMR Post: Broglio et al), but sub-concussive impacts (e.g., soccer heading) that do not result in a concussion are much more common and are speculated to lead to long-term brain alterations. However, no research has evaluated the cumulative effect of repetitive head impacts. A first step towards this goal may be to quantify the amount of head impacts (including sub-concussive) our athletes are experiencing. The purpose of this study was to better describe high school football athletes’ exposure to impacts during a season and career. Researchers followed 95 athletes on the same 3A football team from 2007 to 2010, and recorded how many impacts they received during each practice and game. Head impacts were recorded with helmets that were fitted with an impact tracking system (HITS; head impact telemetry system). Computer software calculated peak linear head acceleration, rotational head acceleration, and HITsp (severity profile; a calculation that uses linear and rotational acceleration as well as impact duration and location). Over the course of the four-year study a total of 101,994 impacts were collected across 190 practices and 50 games. This included 20 concussive events from 19 athletes. On average each player sustained about 652 impacts per 14-week season. The lowest number impacts a player sustained was 5 (kicker) and the highest number of impacts recorded from an athlete was 2,235 (starting defensive tackle). Lineman experienced the greatest annual number of head impacts over an entire season followed sequentially by tight ends, running backs, linebackers, and quarterbacks. The amount of head impacts sustained in practice versus games was different based on position. Annually, the quarterback sustained more impacts during games than in practices, but all other positions obtained equal or greater number of head impacts during practices.
This study had several important findings about sub-concussive impacts, which are often neglected since athletes do not usually show any signs or symptoms of distress (only 20 concussions from 101,994 impacts). The large number of the impacts for those who play football all 4 years in high school is striking. It also interesting to note that all positions, except the quarterback (who is usually not touched in practice), sustained more head impacts during practices than games; probably because of the repetition of their drills. It is important to remember that there is no direct link between the magnitude or frequency of the linear and rotational acceleration on sub-concussive impacts so it is hard to say if the magnitude or frequency of sub-concussive head impacts is more important. Also, the researchers did a 4-year study only 2 of the athletes were included in this program all 4 years. Future research, including longer prospective studies (following a lifetime), should try to confirm if there is an association between sub-concussive impacts, cumulative impacts, and long-term changes in brain structure or function. They should also consider differences among starters versus second and third string players, since starting athletes will have more repetitions in practices and games. Other studies could go a step further and utilize magnetic resonance imaging to view the brain before the season, after the season, and then follow up before the next season to see how the brain changes. These studies could lead to football coaches adjusting practices to minimize head acceleration magnitudes for high school football athletes.
Written by: Jane McDevitt
Reviewed by: Jeffrey Driban
Related Posts:
In a similar study on collegiate football athletes by Schnebel et al in 2007, the Head Impact Telemetry (HIT) System recorded an average of 5,416 head impacts in a typical 4-year career. Results from this study also showed that skill position players received harder impacts and lineman sustained more total impacts compared to other football positions.
Due to the increased number of head impacts that high school and college football players sustain, there must be an increased potential for concussion in this population. If an individual plays 4 years of high school football and 4 years of college football then according to Broglio et al and Schnebel et al’s HIT statistics they could sustain a combined average of 8,024 head impacts! Depending on position, this number of impacts could be even higher.
The real question for me is: what are the effects of these multiple sub-concussive impacts on long-term brain health and function? Current data is conflicting on the long-term, cumulative effects of concussion. Several studies have found that individuals who have suffered from multiple concussions may have long-lasting deficits. (Collins, 1999; Moser, 2005; Moser,2002; Covassin, 2008;Guskiewicz, 2005; Schatz, 2011;Wall, 2006) Oppositely, there is a number of studies that have not found a relationship between concussion and long-lasting neurocognitive effects. (Broglio, 2006; Bruce, 2009; Collie, 2006; Iverson, 2006; Gaetz, 2000;Macciocchi,2001)
Due to these inconsistent conclusions, there is not enough supporting evidence to call for a drastic change in football rules or techniques. The NFL has taken a step in the right direction by cracking down on dangerous plays, but there is still work to be done to improve the safety of play. As a Sports Medicine professional, we need to use our brains and find a concussion solution in order to protect the brains of those we care for.
Like you have pointed out there has been research demonstrating the potential for long lasting deficits due to multiple concussions. However, the problem with the research is that they do not follow the athlete long enough (lifetime) to form a strong connection between multiple concussions and the diseases associated such as Alzheimer’s Disease or Depression. Many of the articles you cited suggest that athletes that had a previous concussion may sustain a second concussion easier (Collins, 2002), they may drop in their memory ability (Iverson, 2004), and did worse on measure of attention and concentration (Moser, 2005). Those studies used retrospective data (concussion history) and did not follow the athletes prospectively. There are those studies such as Collins, 2006 that demonstrate that one concussion does not have a cumulative effect on a second. Authors suggest that if the concussion is completely recovered it should not affect the athlete if they receive a second, or even third.
Though Broglio et al. did show some alarming statistics they did not measure any concussion sign and symptoms after practice so it is hard to say if those impacts had a cumulative effect. Again, to have any strong association data a research study needs to follow an athlete through their lifetime to the possible onset of the disease such as Alzheimer’s.
Currently you are correct our only true defense against concussions is through the enforcement of safe play including correct technique and rules encouraging safe play. Medical professionals need to stay up to date with their evaluation and treatment of concussions. Evaluating a concussion utilizes a battery of tests including SCAT2, BESS, Concussion sign and symptoms checklist, ocular tests, and hopefully a computer assessment (e.g., Headminder, ImPact) with a baseline measurement. Also, knowledge about potential concussion treatment methods including limiting the athletes’ workload, decreasing the athletes’ time on the computer, texting, and TV. There have also been studies suggesting potential pharmaceutical treatments for concussion sign and symptoms. As well as the gradual return to play are the way medical professionals can protect athletes that sustain a concussion.