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

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