Concussions in sport

Concussions, a type of traumatic brain injury, have been a notorious issue in sports, being a notable reason for player suicides and retirements due to chronic traumatic encephalopathy (CTE) from their playing careers.[1] A form of CTE common in boxing is dementia pugilistica (DP). Over 1.6 million Americans have sustained concussion-related injuries, a number that has since then grown in high school and college athletes.[2] Because concussions cannot be seen on X-rays or CT scans, attempts to prevent concussions have been difficult.[3] As of 2012, the four major professional sports leagues in the United States and Canada have concussion policies.[4] Sports-related concussions are generally analyzed by athletic training or medical staff on the sidelines using an evaluation tool for cognitive function known as the Sport Concussion Assessment Tool (SCAT), a symptom severity checklist, and a balance test.[5]

Incidence

It is estimated that as many as 3.8 million concussions occur in the US per year in competitive sports and recreational activities; however, as many as 50% of concussions go unreported. Concussions occur in all sports with the highest incidence in football, hockey, rugby, soccer, and basketball.[5] In addition to concussions caused by a single severe impact, multiple minor impacts may also cause brain injury.[6]

Injury rate per exposure based on sport in collegiate athletes from 1998 to 2004[7]
Sport Injury rate per 1,000 athletic exposures
Women's ice hockey 0.91
Men's spring football (American) 0.54
Men's ice hockey 0.41
Women's soccer 0.41
Men's football (American) 0.37
Men's soccer 0.28
Men's wrestling 0.25
Men's lacrosse 0.25
Women's lacrosse 0.25
Women's basketball 0.22
Women's field hockey 0.18
Men's basketball 0.16
Women's gymnastics 0.16
Women's softball 0.14
Women's volleyball 0.09
Men's baseball 0.07
All sports 0.28

Policies

Major League Baseball

Major League Baseball's policy was first started in 2007, and injured players are examined by a team athletic trainer on the field.[8] On March 29, 2011, MLB and the Major League Baseball Players Association announced that they have created various protocols for the league's concussion policy. The new policy includes four primary components:[9]

National Basketball Association

The National Basketball Association does not have a policy, and team procedures after concussions vary by team.[8]

National Football League

The National Football League's policy was first started in 2007, and injured players are examined on field by the medical team.[8] The league's policy included the "NFL Sidelines Concussion Exam", which requires players who have taken hits to the head to perform tests concerning concentration, thinking and balance.[11] In 2011, the league introduced an assessment test, which combines a symptoms checklist, a limited neurological examination, a cognitive evaluation, and a balance assessment. For a player to be allowed to return, he must be asymptomatic.[12]

National Hockey League

The National Hockey League's concussion policy began in 1997, and players who sustain concussions are evaluated by a team doctor in a quiet room.[8] In March 2011, the NHL adopted guidelines for the league's concussion policy. Before the adoptions, examinations on the bench for concussions was the minimum requirement, but the new guidelines make it mandatory for players showing concussion-like symptoms to be examined by a doctor in the locker room.[13]

"We celebrate the big hit, we don't like the big head hit. There is an important distinction because we celebrate body-checking."[13]
—NHL Commissioner Gary Bettman

Table

League Year policy first introduced Year baseline testing occurred Year current policy became effective First step after injury Person who approves/denies player to return Person who decides player return
NFL 2007 2008 2009 Evaluation by medical team Medical staff Medical staff/Consultant
MLB 2007 2011 2007 Evaluation by an athletic trainer using National Association Guidelines Medical staff Head physician/Medical director
NBA Never Never Never Depends on team Depends on team Depends on team
NHL 1997 1997 2011 Neuropsychological evaluation by team doctor off rink Team doctor Team doctor
MLS 2011 2003 2011 Evaluation by medical team Team physician Team physician/Neuropsychologist
NASCAR 2003 2003 2003 Ambulance to infield care center NASCAR NASCAR

Concussions in other sports

American football

American football has been known to have the most concussions out of any other sport in the United States, with over 250,000 injuries reported annually in football players, with 20% of high-school football players experiencing a concussion every year.[14] In 2000, researchers from the Sports Medicine Research Laboratory at the University of North Carolina at Chapel Hill analyzed 17,549 players from 242 different school. Research eventually revealed that 888 (5.1%) of the players analyzed have at least one concussion a season, and 131 (14.7%) of them have had another concussion the year later. Division III and high-school players have a higher tendecy to sustain a concussion than Division II and Division I players.[15] In 2001, the National Football League Players Association partnered with the UNC to determine whether professional football players suffer any health effects after any injuries, with the findings being criticized by the NFL for being unreliable due to being based on self-reporting by the players.[16]

Association football

Association football— also known as "soccer"— has been one of the world's major sports to have concussions. Even though 50-80% of injuries in football are directed to the legs, head injuries have been shown to account for between 4 and 22% of football injuries, with a possibility that heading the ball could damage the head, as the ball could travel at 100 km/hour. However, most professional footballers reported that they experienced head injuries from colliding with other players and the ground.[17] A Norwegian study consisting of current and former players of the Norway national football team found out that 3% of the active and 30% of the former players had persistent symptoms of concussions, and that 35% of the active and 32% of that former players had abnormal electroencephalogram (EEG).[18] Another example is found on Czech goalkeeper Petr Čech who once suffered from a severe concussion during the 2006-07 English Premier League season in a match between his club Chelsea and Reading. During the match Čech and Reading midfielder Stephen Hunt both challenged each other for the ball inside Chelsea's penalty area, which led to Hunt's right knee impacting Čech's head, knocking the keeper out.[19] Čech underwent surgery for a depressed skull fracture and was told that he would miss a year of playing football. Čech resumed his goalkeeper duties on January 20, 2007 in a match against Liverpool, now wearing a rugby helmet to protect his now-weakened skull.

A growing topic recently is concussions in girls soccer, predominantly in high-school girls. The country is in the midst of “a concussion crisis” and that studies show girls are reporting nearly twice as many concussions as boys in the sports they both play. Not only that, but the number of girls suffering concussions in soccer accounts for the second largest amount of all concussions reported by young athletes.[20] In 2010, more highschool soccer players suffered concussions than basketball, baseball, wrestling, and softball players combined, according to the Center for Injury Research and Policy in Columbus, Ohio.[21] What is even more worrisome is that, according to a study posted to the web site of the JAMA Pediatrics medical journal, many girls are not getting the necessary care and prevention regarding concussions. Even more worrisome is that 56 percent of players (or their families) reporting concussion symptoms never sought treatment.[22] Playing through concussion makes people more vulnerable to getting hit again, and having longer and more severe symptoms. A second blow can cause a rare condition known as second-impact syndrome, which can result in severe injury or death. Second-impact syndrome typically occurs in people under 20, O’Kane said. This has brought up concerns based on it may be beneficial to teach proper heading techniques to younger players, and there may be situations where those players shouldn’t head the ball.[23]

On November 2, 2013 in a match between Tottenham and Everton, Tottenham goal keeper Hugo Lloris sustained a blow to the head by on -coming player Romelu Lukaku's knee. The blow left Lloris knocked out on the ground. Reluctantly manager Andre Villas Boas decided to leave the player on after regaining consciousnesses and having passed a medical assessment. This breaks the rule of The PFA, stating it should be made mandatory for any player who has lost consciousness to be substituted.[24]

There has been a widespread debate on protective head gear in soccer. Known as a sport associated with intricate footwork, speed, and well-timed passes, soccer also is classified as a high- to moderate-intensity contact/collision sport, with rates of head injury and concussion similar to those seen in football, ice hockey, lacrosse, and rugby. While the benefits of helmets and other head protection are more obvious in the latter sports, the role of headgear in soccer has been and still is unclear. No headband or headgear can prevent another concussion in this young athlete. Although some headgear products may decrease the force of the impact during a hit, they cannot eliminate the possibility of concussion.[25]

There are clear rules from FIFA regarding what to do when a player gets a concussion. Its [FIFA] detailed guidelines say that a player who has been knocked unconscious should not play again that day. The rules do however allow for "a transient alteration of conscious level" following a head injury, which says a player can return to play following assessment by medical staff. The rules also state that a player who is injured with head damage is not to be played for five days.[26]

According to a 2012 study published by ScienceDirect, soccer has the highest injury rate per athlete-exposure among 7- to 13-year-old children.[27]

Auto racing

The death of Dale Earnhardt at the 2001 Daytona 500, along with those of Kenny Irwin, Adam Petty and Tony Roper in 2000, and serious injuries sustained by Steve Park in a wreck in September 2001 at Darlington, led to NASCAR establishing numerous policies to assist in driver safety, such as the introduction of the Car of Tomorrow. Drivers were eventually instructed to wear both head and neck restraints, and SAFER barriers have been installed on racetrack walls, with foam-padded supports on each side of the helmet that would allow a driver's head to move in the event of a crash. Despite this, 29 concussions have been identified since 2004, and 12 of them have happened since 2007.[28]

In 2012, when Dale Earnhardt, Jr. suffered a concussion after being involved in a crash at Talladega in October, NASCAR expressed consideration in adding baseline testing to its concussion policies. NASCAR was one of few motorsport organizations that do not have baseline testing,[29] though that ended in 2014, as baseline testing started being performed at the start of the seasons.[30]

Basketball

In the 2005 high school basketball year, 3.6% of reported injuries were concussions, with 30.5% of activity report when a concussion occurred being rebounds.[31]

Boxing

Despite boxing's violent nature, a National Safety Council report in 1996 ranked amateur boxing as the safest contact sport in America.[32] However, concussions are one of the most serious injuries that can occur from boxing, and in an 80-year span from 1918 to 1998, there were 659 boxers who died from brain injury.[33]

Ice hockey

Ice hockey has also been known to have concussions inflict numerous players. Because of this, the NHL made hockey helmets mandatory in the 1979–80 NHL season.[34] According to a data release by the National Academy of Neuropsychology's Sports Concussion Symposium, from 2006 to 2011, 765 NHL players have been diagnosed with a concussion.[35] At the Mayo Clinic Sports Medicine Center Ice Hockey Summit: Action on Concussion conference in 2010, a panel made a recommendation that blows to the head are to be prohibited, and to outlaw body checking by 11- and 12-year olds. For the 2010–11 NHL season, the NHL prohibited blindside hits to the head, but did not ban hits to the face. The conference also urged the NHL and its minor entities to join the International Ice Hockey Federation, the NCAA and the Ontario Hockey League in banning any contact to the head.[36]

Prevention could be helped by professional sports such as the National Hockey League pushing towards making hockey safer. Concussions have become a more common injury in hockey today and are being critiqued under a microscope for both there immediate and long-lasting effects. Even with the increase in concern with concussions there still needs to be more done to cut down on the number of concussions we see in today's game.[37] Concussion symptoms can last for an undetermined amount of time depending on the player and the severity of the concussion. There is also the potential of post-concussion syndrome, which can last for months after the concussion. A concussion will affect the way a person's brain works.[38] Concussions damage the brain of a person and the brain controls everything in the body so to limit this severe injury to the highest percentage possible would be in everybody’s best interest. National Hockey League Commissioners have been pushing towards stricter rules and longer suspensions to crack down on concussions. There have been great strides taken in changing the rules to help concussion prevention but officials still have to continue to look into this considering the game is evolving at an extremely fast pace. Players also need to make it a responsibility within themselves to protect each other and not take runs at each other with a player with their head down. Taking all these things into consideration, this could help the prevention of concussions in the National Hockey League considerably.

Rugby union

Concussions are also a significant factor in rugby union, another full-contact sport. The sport's world governing body, the International Rugby Board (IRB), has issued a highly detailed policy for dealing with injured players with suspected concussions. Under the policy established in 2011, a player suffering from a suspected concussion is not allowed to return to play in that game. Players are not cleared to play after the injury for a minimum of 21 days, unless they are being supervised in their recovery by a medical practitioner. Even when medical advice is present, players must complete a multi-step monitoring process before being cleared to play again; this process requires a minimum of six days.[39] In 2012, the IRB modified the policy, instituting a Pitchside Suspected Concussion Assessment (PSCA), under which players suspected of having suffered concussions are to leave the field for 5 minutes while doctors assess their condition via a series of questions. Players who pass the PSCA are allowed to return to play.[40]

However, an incident during the third Test of the 2013 Lions tour of Australia led to criticism of the current protocols. During that match, Australian George Smith clashed heads with the Lions' Richard Hibbard and was sent to pitchside. According to ESPN's UK channel, "despite looking dazed and confused, Smith passed the PSCA and was back on the field minutes later."[40] in 2013, former Scotland international Rory Lamont charged that the current concussion protocols can easily be manipulated. A key part of the current protocols is the "Cogsport" test (also known as COG), a computer-based test of cognitive function that each player undergoes before the start of a new season. According to Lamont,

To be declared fit you must reach your baseline score which you set during your pre-season, when you were considered to have 100% cognitive function. Players can view the baseline test as an obstacle in their way for getting back playing. To achieve an accurate score, you must pay full attention. The conflict of interest is this: the better score you set in the baseline test, the more difficult it will it be to pass the test after concussion. Set a high score and you might end up missing more games than you would like; put in 80% effort and it will be easier to pass the COG test after concussion. Players will deliberately cheat the protocol by putting in a sub-maximal effort when setting their baseline. Without maximum concentration and effort, the COG test will be unreliable for identifying if a player is suffering concussive symptoms.[41]

Lamont was also critical of the PSCA, noting,

The problem with the PSCA is a concussed player can pass the assessment. I know from first hand experience it can be quite ineffective in deciding if a player is concussed. It is argued that allowing the five-minutes assessment is better than zero minutes but it is not as clear cut as one might hope. Concussion symptoms regularly take 10 minutes or longer to actually present. Consequently the five-minute PSCA may be giving concussed players a license to return to the field.[41]

Female sports

Numerous reports have indicated that female athletes suffer more concussions compared to male athletes. A December 2008 report states that 29,167 female high school soccer players suffered from concussions in 2005, compared to 20,929 male players. In high school basketball, 12,923 girls suffered from concussions while only 3,823 boys did. Girls also sustained more concussions in softball, compared to boys in baseball.[42] Female athletes also had longer recovery times than males, and also had lower scores on visual memory tests. One of the possible reasons that is suggested by various researchers as to why girls have longer recovery times include the possibility that the greater rate of blood flow in the brain for females might have affected the recovery times.[43]

Women's ice hockey was reported as one of the most dangerous sports in the NCAA, as the concussion rate is 2.72 per 1,000 player hours. Even though men's ice hockey allows body checking, which is illegal in the women's game, the rate of concussions for men is 46% lower, at 1.47 per 1,000 player hours. Women’s basketball is one of the top women’s sports with the highest risks of getting a concussion. With high competition comes a higher risk of injuries. College level sports can be very physical, especially women’s basketball (The Epidemiology). Concussions are associated with different activities. For women, they have a greater risk of getting a concussion by dribbling/ball handling rather than defending. Also it was found that female college basketball players typically receive concussions during games rather than practices. The reasoning for this could be that they are competing at a higher level, and are more aggressive in games than practices. Not only just in concussions, but for overall injuries (The Epidemiology)."The Epidemiology of Sport-Related Concussion." Clin Sports Med, 1 Jan. 2012. Web. 8 Feb. 2013. College football also has lower concussion rates than women's hockey, with a rate of 2.34 per 1,000.[44]

Prevention efforts and technology

There have been numerous attempts at preventing concussions, such as the establishment of the PACE (Protecting Athletes Through Concussion Education) Program, which works with the imPACT system, which is currently used by every NFL and some NHL teams.[45] In 2008, the Arena Football League tested an impact monitor created by Schutt Sports called the "Shockometer", which is a triangular device attached to the back of football helmets that has a light on the device that turns red when a concussion occurs.[46] Riddell has also created the Head Impact Telemetry System (HITS) and Sideline Response System (SRS) to record the frequency and severity of player hits during practices and games. On every helmet with the system, MX Encoders are implemented, which can automatically record every hit.[47] Eight NFL teams had originally planned to use the system in the 2010 season, but the NFL Players Association ultimately blocked its use.[48] Other impact-detection devices include CheckLight, by Reebok and MC10.,[49] and the online test providers ImPACT Test and XLNTbrain both of which establish cognitive function baselines against which the athlete is monitored over time.

Media coverage

In 2012, film producer Steve James created the documentary film Head Games, interviewing former NHL player Keith Primeau, and the parents of Owen Thomas, who hung himself after sustaining brain damage during his football career at Penn.[50] The documentary also interviewed former athletes Christopher Nowinski, Cindy Parlow, and New York Times reporter Alan Schwarz, among other athletes, journalists, and medical researchers.[51] Significant media coverage of concussions in sports, particularly American football, began after the death of Mike Webster. This includes newspaper and magazine spreads, television newsmagazine episodes, and the "Football High"[52] and "League of Denial"[53] (also the title of a book on the subject) episodes of Frontline, as well as work by political sports journalist Dave Zirin.[54]

See also

References

  1. ↑ Kingston, Gary (2012-05-29). "Concussion sends Mike Robertson into retirement". Vancouversun.com. Retrieved 2012-06-30.
  2. ↑ "Girls, sports and concussions". Philly.com. 2012-05-23. Retrieved 2012-07-14.
  3. ↑ "Think First - Pensez d'Abord". Thinkfirst.ca. Retrieved 2012-08-04.
  4. ↑ "Concussions in sports - NFL Topics - ESPN". Espn.go.com. Retrieved 2012-06-30.
  5. ↑ 5.0 5.1 Harmon, K. G., Drezner, J. A., Gammons, M., Guskiewicz, K. M., Halstead, M., Herring, S. A., ... & Roberts, W. O. (2013). American Medical Society for Sports Medicine position statement: concussion in sport. British journal of sports medicine, 47(1), 15-26.
  6. ↑ Rivara, G R (2014). "Sports-Related Concussions in Youth: Improving the Science, Changing the Culture". Institute of Medicine; National Research Council. Retrieved 12 November 2014.
  7. ↑ Hootman J, *** R, and Agel J. Epidemiology of collegiate injuries for 15 sports: Summary and recommendations for injury prevention initiatives. J Athlete Train 42: 311-319, 2007
  8. ↑ 8.0 8.1 8.2 8.3 Brady, Erik; Falgoust, J. Michael (2011-10-25). "Concussions now a hot issue as leagues toughen policies". Usatoday.Com. Retrieved 2012-06-30.
  9. ↑ Stephania BellFantasy SportsFollowArchive (2011-04-01). "7-day DL, return-to-play protocols part of MLB's new concussion policy - Fantasy Baseball - ESPN". Sports.espn.go.com. Retrieved 2012-06-30.
  10. ↑ 10.0 10.1 "Baseball establishes seven-day DL in concussion policy". Content.usatoday.com. 2011-03-30. Retrieved 2012-06-30.
  11. ↑ "NFL to require sideline test after head blows – - CNN.com Blogs". Thechart.blogs.cnn.com. 2011-02-25. Retrieved 2012-06-30.
  12. ↑ Mayer, Larry (2012-11-12). "Cutler on mend after suffering concussion". Chicago Bears. Retrieved 2012-11-12.
  13. ↑ 13.0 13.1 "NHL commissioner Gary Bettman pleased with league's concussion protocol - ESPN". Sports.espn.go.com. 2011-04-23. Retrieved 2012-06-30.
  14. ↑ SMH. "Sport-Related Concussion". Hughston.com. Retrieved 2012-07-01.
  15. ↑ "Neuroscience for Kids - Football Concussions". Faculty.washington.edu. Retrieved 2012-07-01.
  16. ↑ Hadhazy, Adam (2008-09-02). "Concussions Exact Toll on Football Players Long After They Retire". Scientific American. Retrieved 2012-07-01.
  17. ↑ "Neuroscience for Kids - Soccer". Faculty.washington.edu. Retrieved 2012-07-04.
  18. ↑ "Head and neck injuries in soccer. Impact of minor... [Sports Med. 1992] - PubMed - NCBI". Ncbi.nlm.nih.gov. 2012-05-24. Retrieved 2012-07-04.
  19. ↑ "Mourinho angry as keepers injured". BBC Sport. 14 October 2006. Retrieved 16 October 2006.
  20. ↑ Snow, Kate, Sarah Koch, Deirdre Cohen, and Jessica Hopper. "Concussion Crisis Growing in Girls' Soccer." NBC News. NBC, 9 May 2012. Web. 16 Feb. 2014.
  21. ↑ Cantu, Robert C., and Mark Hyman. "Soccer." Concussions and Our Kids: America's Leading Expert on How to Protect Young Athletes and Keep Sports Safe. Boston: Houghton Mifflin Harcourt, 2012. 40+. Print.
  22. ↑ Cook, Bob. "Study Reveals Many Girls Soccer Players Stay On Field Despite Concussions." Forbes. Forbes Magazine, 21 Jan. 2014. Web. 06 May 2014.
  23. ↑ Princing, McKenna. "Girls Frequently Play Soccer through Concussion, Study Finds." UW Today. University of Washington, 20 Jan. 2014. Web. 06 May 2014.
  24. ↑ Gibson, Owen. "Concussion Rules under Spotlight in Wake of Hugo Lloris Row." The Guardian. Guardian News and Media, 05 Nov. 2013. Web. 17 Feb. 2014.
  25. ↑ Malonie, Jamie, Linda Nield, and Matthew Livley. "Can Headgear Halt Soccer Concussions?" Consultant For Pediatritions. Consultant For Pediatritions, July 2013. Web. 04 Mar. 2014
  26. ↑ Gibson, Owen. "Concussion Rules under Spotlight in Wake of Hugo Lloris Row." The Guardian. Guardian News and Media, 05 Nov. 2013. Web. 17 Feb. 2014.
  27. ↑ Levy, Michael L., Aimen S. Kasasbeh, Lissa C. Baird, Chiazo Amene, Jeff Skeen, and Larry Marshall. "Concussions in Soccer: A Current Understanding." Science Direct. Science Direct, Nov. 2012. Web. 12 Feb. 2014.
  28. ↑ "NASCAR drivers have concussion concerns - Racing - SI.com". Sportsillustrated.cnn.com. 2012-02-21. Retrieved 2012-07-01.
  29. ↑ Bandoim, Lana. "NASCAR May Be Considering Changes to Its Concussion Policies: Fan View". Yahoo! Sports. Retrieved 2012-10-21.
  30. ↑ Gluck, Jeff (2013-10-24). "NASCAR will mandate baseline concussion testing in 2014". USA Today. Retrieved 2013-10-24.
  31. ↑ "Concussions becoming a concern in basketball | basketball, becoming, concern - Sports - Colorado Springs Gazette, CO". Gazette.com. Retrieved 2012-07-04.
  32. ↑ "Concussions in Boxing | iSport.com". Boxing.isport.com. Retrieved 2012-07-01.
  33. ↑ "–". Usatoday.com. 2011-08-29. Retrieved 2012-07-04.
  34. ↑ Stubbs, Dave (2012-06-19). "Dave Stubbs: Max Pacioretty richly deserves Masterton trophy". Montrealgazette.com. Retrieved 2012-07-14.
  35. ↑ "Bigger Hockey Players Causing More Concussions". LiveScience. 2008-11-10. Retrieved 2012-07-04.
  36. ↑ Klein, Jeff (2010-10-20). "Hockey Urged to Ban All Blows to Head by Concussions Panel". The New York Times.
  37. ↑ Proteau, Adam. "NHL Can Do More To Prevent Concussions". The Hockey News. Retrieved October 30, 2013.
  38. ↑ Wedro, Benjamin. "Concussion". MedicineNet. Retrieved October 30, 2013.
  39. ↑ "IRB Concussion Guidelines". International Rugby Board. 2011-05-24. Retrieved 2013-02-16.
  40. ↑ 40.0 40.1 "Lamont: Players are cheating concussion tests". ESPN Scrum. 27 July 2013. Retrieved 26 December 2013.
  41. ↑ 41.0 41.1 Lamont, Rory (19 December 2013). "'Players are deliberately cheating concussion tests'". ESPN Scrum. Retrieved 26 December 2013.
  42. ↑ "High school headaches: Girls' concussions outnumber boys' in most sports". News.medill.northwestern.edu. Retrieved 2012-07-04.
  43. ↑ "Concussions: Girls Have Longer Recovery Time". Webmd.com. 2012-05-11. Retrieved 2012-07-04.
  44. ↑ Klein, Jeff Z. (2010-10-19). "Women's Hockey, a Most Dangerous Game - NYTimes.com". Slapshot.blogs.nytimes.com. Retrieved 2012-07-04.
  45. ↑ "Drew Brees Teams Up Against Concussions in School Sports - ABC News". Abcnews.go.com. 2012-06-26. Retrieved 2012-07-04.
  46. ↑ "AFL-Test-Drives-Schutt’S-Shockometer / News". NFLPlayers.com. 2008-05-22. Retrieved 2012-07-04.
  47. ↑ "HITS™ Technology". Riddell. Retrieved 2012-06-26.
  48. ↑ "Failure to use HIT system exposes league to future concussion liability | ProFootballTalk". Profootballtalk.nbcsports.com. Retrieved 2012-06-26.
  49. ↑ http://www.bostonglobe.com/business/2013/07/14/reebok-introduce-concussion-sensor-for-sports/s7L509zIM5lBrHXb0ylDDM/story.html
  50. ↑ "'Head Games' Film Focuses on Concussions, Asks If Enough is Being Done". Athleticbusiness.com. Retrieved 2012-07-14.
  51. ↑ "Head Games: The People". Headgamesthefilm.com. Retrieved 2012-07-14.
  52. ↑ Football High
  53. ↑ League of Denial
  54. ↑ The Collision of Sports and Politics