Heads up: American football collision course

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  • Published: Aug 1, 2013
  • Author: David Bradley
  • Channels: MRI Spectroscopy
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Cracking nuts

A new measure of the effects of cranial impact in American football players can be used in conjunction with magnetic resonance imaging (MRI) and neurological testing to assess the cumulative effect on players before and after the American football season.

A new measure of the effects of cranial impact in American football players can be used in conjunction with magnetic resonance imaging (MRI) and neurological testing to assess the cumulative effect on players before and after the American football season.

Scientists at Wake Forest Baptist Medical Center in North Carolina have developed the novel metric, known as Risk Weighted Cumulative Exposure (RWE), to allow them to capture the exposure of players to the risk of concussion over the course of a football season by measuring the frequency and magnitude of all impacts. The metric was developed by biomedical engineers Joel Stitzel, Jillian Urban and colleagues at Wake Forest Baptist and the Virginia Tech - Wake Forest University School of Biomedical Engineering and Sciences. Details have now been published in the online edition of the Annals of Biomedical Engineering.

The team collected data from high school football games and practices during the sport's season and looked at the effects in terms of linear and rotational acceleration separately on the overall risk of injury to layers. They also recorded the combined probability of injury associated with both types of movement and then developed the RWE to give them cumulative risk of injury.

Stats and metrics

“This metric gives us a way to look at a large number of players and the hits they’ve incurred while playing football," Stitzel explains. "We know that young players are constantly experiencing low-level hits that don't cause visible injury, but there hasn't been a good way to measure the associated risk of concussion." Concussion is a rather too common sports-related head injury and participants in American football tend to have the highest rate among US high school athletes, according to the study. It is estimated that nearly 1.1 million students play high school football in the USA. However, research on the biomechanics of football-related head impacts traditionally has concentrated on the collegiate level rather than on the high school level. With such a large number of players in the sport, it is critical to understand the risk associated with different levels of impact and accurately estimate cumulative concussion risk over the course of a practice, game and the season or a player's lifetime at the game, Stitzel adds.

The Wake Forest Baptist study involved using sensor pads in the players' protective helmets and recording the linear and rotational acceleration experienced by the players. They gathered data from forty players experience a staggering 16,502 impacts over the course of just a single American football season. They then analysed the data at the group and individual player level. The researchers weighted impacts according to the associated risk from linear acceleration and rotational acceleration alone, as well as to the combined probability of injury associated with both. This, they say, is an improved method of capturing the cumulative effects from each impact because it accounts for nonlinear relationships between impact magnitude and the associated risk of injury.

Safer helmets

"All hits involve both linear and rotational acceleration, but rotation coveys the idea that your head is pivoting about the neck whereas linear acceleration is experienced from a direct blow in more of a straight line through the centre of mass of the head," Stitzel explains. The median impact for each player ranged from 15.2 to 27.0 g, with an average value of 21.7 g, which shows the wide variability in the force of impacts. The units "g" are in terms of "acceleration due to gravity".

Perhaps not surprisingly, the team found that the impact frequency was greater during games (15.5) than during practices (9.4); presumably when players are acting in earnest to win a game rather than simply assimilating skills, technique and fitness. However, overall exposure over the course of the season was greater during practices, presumably as there are more repeat manoeuvres as players practice specific actions used in a game.

The researchers suggest that the information and knowledge they have gleaned from the study might be useful in helping coaches and teams reduce exposure to head impacts during practices by teaching better tackling techniques. Additionally, the study found a wide variation in player exposure within the team, with a 22-fold variation in the exposure per impact for practices and a 47-fold variation in the exposure per impact for games. This information too, albeit on a small sample size, might be useful in improving coaching techniques. Overall, such studies are important for sports scientists, coaches and players hoping to understand the biomechanical basis of head injuries in sport, specifically in this instance, American football. According to Stitzel, the new metric captures fully a player's exposure over the course of the season and will be coupled to MRI scans and neurological tests in the future to garner a wider view of risk in such high-contact sports. The researchers suggest that the work might ultimately be used by equipment designers and manufacturers to improve helmet safety.

The next step, Stitzel told SpectroscopyNOW is, "to study imaging data, study cognitive testing data, continue to follow as many players as we can. We hope the study will have an impact on practices, helmet safety, and overall safety of the game to reduce overall exposure to players while not impacting quality of the game."

Related Links

Ann Annals of Biomed Eng 2013, online: "Head Impact Exposure in Youth Football: High School Ages 14 to 18 Years and Cumulative Impact Analysis"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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