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Author: Robert C. Cantu
A person can have functional abnormalities of the brain in the absence of symptoms and a diagnosis of concussion. This creates particular risks for athletes, as injury may go undetected during and even after a drill or game.
What can be done to reduce the risk of concussion and subconcussive head trauma among athletes? There are four main areas to consider in such efforts: protective equipment, increasing the neck strength of athletes, changes to game and practice rules, and education to modify behavior and exposure.
Helmets and other protective headgear can attenuate the highly focal, linear impacts that lead to skull fracture, concussions, and intracranial bleeding, but they are not very effective in reducing rotational accelerations. The human brain is highly sensitive to injury from rotational impacts, but no helmet has been designed that can dampen shear stresses from such impacts. For this reason helmets will likely never be the major way to reduce concussions.
Can increased neck strength and bracing for impact reduce the likelihood of concussion? At the most basic level, collisions are governed by Newton’s second law: force = mass × acceleration. If a small mass is hit with a given force, a significant acceleration will occur, compared to a large mass hit with the same force. Hits of over 20 g in acceleration of the head can occur in the act of tackling or being tackled. Increasing the mass can decrease the acceleration that causes concussion.
Two populations at increased risk for concussion are women, who have roughly two to three times the incidence of concussion in the same sports men play, and youth. Both tend to have weaker necks than adult men.
Strengthening the neck—by increasing its girth and stiffness—and bracing for impact protect the head by connecting it more solidly to the rest of the body. The acceleration of the head upon impact is reduced as the incoming force meets a resistance more comparable to the mass of the body rather than the small mass of the head (i.e., conservation of momentum).
We recently conducted a study that showed that athletes with the greatest neck strength had the fewest concussions, and those with the least had the highest number of concussions (Collins et al. 2014). We found that, adjusted for gender and sport, essentially one pound of increased neck strength decreased the odds for a concussion by 5 percent.
Neck strength can be reliably measured with a very inexpensive device and minimal training (figure 1). Adding neck strengthening exercises to training regimens could be a viable and attainable part of a concussion reduction plan for athletes.
Game and Practice Rules
The incidence of concussion can be reduced by rule changes, especially those that reduce hits to the head. Such rule changes are being adopted or considered for both professional and youth athletes.
Changes in the NFL
Concussions and subconcussive blows can be dramatically reduced in helmet-to-helmet collisions by limiting full contact in practice. The NFL allows 14 full contact practices during the 18 weeks of the season—less than one a week—and none in the off-season.
Another significant new NFL rule prohibits above-the-shoulder hits to a “defenseless player,” defined as a player who cannot see the approach of the impact. Penalties range from 15 yards to fines and removal from the game, depending on the circumstances. The ability of a player to brace for impact, for example by engaging neck strength, is crucial to prevent brain injury.
A further factor in reducing the incidence of concussion is moving the kickoff up to the 35-yard line. The kickoff runback is recognized as the most dangerous play in football (per seconds of play). As a result of this change the ball is run back less than 50 percent of the time, eliminating half of these risky episodes.
During practice, tackling drills in which the player is not taken to the ground or a robot is used also reduce concussion risk.
Thanks to these changes, a comparison of annual data from the National Football League (NFL)1 shows a 25 percent reduction in concussion incidence from 2013 to 2014 (the concussion rate per game in the NFL was 0.43 in 2014). And concussions from helmet-to-helmet hits, the most common cause of concussion, declined 28 percent from 2013 to 2014. From 2012 to 2014 season concussions went down 43 percent.
Changes for Youth Athletes
A program called “Practice Like the Pros” can decrease the risk of brain trauma for young athletes by bringing some of the improved professional football conventions to youth and college athletes. The program minimizes the risk of injury in practice by tackling without bringing the opponent to the ground.
Education can reduce the incidence of subconcussive and concussive trauma by teaching athletes to develop an awareness of their own concussion risk and alter their behavior accordingly. They may choose to play fewer or different sports, modify their hours of practice, or change their style of play.
Rules that limit the number of hits to an athlete’s head in a week, month, or season can also reduce the incidence of head trauma. It is ironic that there are pitch counts in youth baseball to prevent ulnar collateral ligament injuries, which are reparable, but not hit counts to the head (in football or any other sport) to lower the risk of traumatic brain injury. Hit counts have been shown to work.
In one study of three youth football teams (ages 9 to 12), one team had an average of 145 hits during the season, while another was as low as 61 (Cobb et al. 2013). The difference between the teams was the way the coach ran the practices and taught tackling techniques.
Protective equipment has not been proven to significantly reduce overall concussion risk. Instead, a number of behavioral and rule changes can improve protection from head injury. Neck strengthening and bracing for impact can protect against brain trauma. Changes in the NFL’s competition play rules can reduce injuries substantially. And athletes can modify their exposure and behavior through education. As with any change, each risk strategy must be carefully examined to prevent unintended consequences that result in other types of injury.
Cobb BR, Urban JE, Davenport EM, Rowson S, Duma SM, Maldjian JA, Whitlow CT, Powers AK, Stitzel JD. 2013. Head impact exposure in youth football: Elementary school ages 9–12 years and the effect of practice structure. Annals of Biomedical Engineering 41(12):2463–2473.
Collins CL, Fletcher EN, Fields, SK, Kluchurosky L, Rohrkemper MK, Comstock RD, Cantu RC. 2014. Neck strength: A protective factor reducing risk for concussion in high school sports. Journal of Primary Prevention 35(5):309–319.
1 I serve as a senior advisor to the NFL’s Head, Neck, and Spine Committee