Concussions in American football

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Debate regarding the health effects of concussions on American football players has caused considerable controversy. Concussions and other types of play-related traumatic brain injuries had been proposed as a major cause of player suicides and other symptoms after retirement including memory loss, depression and chronic traumatic encephalopathy (CTE).

The list of ex-NFL players that have either presented post-mortem with CTE, or otherwise have either reported symptoms or been diagnosed with CTE, continues to grow.

Concussions in the National Football League[edit]

There has been a problem for about 20 years regarding the longterm damage of repeated concussions among National Football League (NFL) players, often as a result of contradicting study results published by the NFL. However, by 2010, the NFL finally acknowledged that many of its ex-players were suffering from Chronic traumatic encephalopathy ('CTE').[1]

In 1994, then NFL Commissioner Paul Tagliabue approved the creation of the MTBI Committee with the stated goal of studying the effects of concussions and sub-concussive injury in NFL players. Tagliabue appointed rheumatologist Dr. Elliot Pellman to chair the committee.[2] Pellman's appointment was met with harsh criticism, because he is not a neurologist or neuropsychologist and often admitted ignorance about head injuries.[2]

The same year, the National Institute for Occupational Safety and Health (NIOSH) reported a statistically significant increase in the risk of neurological disorders such as amyotrophic lateral sclerosis (ALS) in retired football players, which furthered public knowledge about the risk of long-term neurocognitive disease related to repeated head impacts.[3] Despite the NIOSH study, Pellman and the MTBI Committee drew their own conclusions that continued to contradict these findings and those of other organizations. Biomechanical engineers and neurosurgeons informed the Committee that the helmet safety standard at that time was insufficient to minimize the risk of concussions.[4]

The MTBI Committee began studying the nature of tackle plays resulting in concussive impacts and developing its own biomechanical analysis of the effect of these forces on the brain.[5] It started publishing study results in 2003 that stated there were no long-term negative health consequences associated with concussions sustained by NFL players. A six-year study by the Committee concluded that, "Players who are concussed and return to the same game have fewer initial signs and symptoms than those removed from play. Return to play does not involve a significant risk of a second injury either in the same game or during the season."[6]

Other organizations continued to publish study results that linked repeated concussions and long-term health problems contrary to reports by the MTBI Committee. A 2003 report by the Center for the Study of Retired Athletes at the University of North Carolina, for example, found a connection between numerous concussions and depression among former professional football players. Further, the Center's follow-up study in 2005 associated both brain impairment and Alzheimer's disease with retired NFL players who had histories of concussions.[7]

A 2004 doctoral dissertation by Don Brady examined NFL Players’ knowledge of concussions, studying both active and retired National Football League Players' knowledge of concussions. Dr. Brady's findings concluded: that many NFL players lacked accurate and essential knowledge pertaining to various aspects of a concussion; that the preponderance of credible experimental and clinical evidence pertaining to the adverse effects of concussion indicates that the brain is injured as a result of a concussion; that the altered cell functioning and cell death along with subtle to more visible neurological, neurocognitive, psychological, and other medical problems reflect a diverse range of lifelong negative consequences of a concussion / brain injury; and that sports team health-care personnel need to focus primarily on the athletes’ health and well-being, and not minimize an injury or primarily concentrate on the players’ capacity to perform on the field. This expanded focus of health care is necessary in order to avoid any real or perceived conflicts of interest emerging in the concussion research, concussion management and related return to play decision-making process. .[8]

In addition to the studies that continued to contradict the work of the MTBI Committee, renowned experts and sports journalists wrote critical reviews of the Committee's studies. Dr. Robert Cantu of the American College of Sports Medicine noted bias in the committee's extremely small sample size and held that no conclusions should be drawn from the NFL's studies.[9] In an ESPN Magazine article titled "Doctor Yes," Peter Keating criticized Pellman and the MTBI Committee's work and argued that the "... Committee has drawn a number of important conclusions about head trauma and how to treat it that contradict the research and experiences of many other doctors who treat sports concussions, not to mention the players who have suffered them."[2]

More studies continued to associate repetitive head injuries with neurological problems later in life. Dr. Kevin Guskiewicz, Director of the Center for the Study of Retired Athletes in the Department of Exercise and Sport Science at the University of North Carolina, analyzed data from a 2007 study of nearly 2,500 former NFL players. He found about 11 percent of the study participants suffered from clinical depression, with a threefold increased risk in former players who had a history of three or four concussions.[10] The following year, the NFL commissioned the University of Michigan Institute for Social Research to conduct a study involving more than 1,000 former NFL players. The results reported that Alzheimer's disease or similar diseases appear to have been diagnosed in former NFL players vastly more often than in the general population at a rate of 19 times the normal rate for men ages 30 through 49. The NFL responded to these results by claiming the study was incomplete.[11]

In October 2009, NFL Commissioner Roger Goodell and the NFL Concussion Committee were called before Congress to defend their policies against allegations of neglect.[12][13] Goodell provided testimony, but was unable to answer many questions, as none of the primary authors of the league’s research, Dr. Ira Casson, David Viano, or Dr. Elliot Pellman were present.[12][13] As a result of this incident and pressure from the NFL Players Association, The NFL released a comprehensive overhaul of the league concussion policy in November and December 2009.[14] The policy expanded the list of symptoms that would prevent a player from returning to a game or practice on the same day their injury occurred.[14][15][16]

With continued pressure to protect players, the NFL began preventing players knocked unconscious by a concussion from returning to a game or practice, a policy that applied to Detroit Lions running back Jahvid Best in 2009.[17] Various players have filed lawsuits against the league for the concussions, accusing the league of hiding information that linked head trauma to permanent brain damage, Alzheimer's disease, and dementia.[18][19] Some teams chose not to draft certain players in the NFL Draft due to their past concussion history. According to an Outside the Lines report, the head impact telemetry system (HITS) was in question by the League, although Dr. University, a professor at the University of North Carolina, said the system is functional.[20] The technology could detect and measure the impact of blows to the head in real time during a game, but no such measurement exists in the league at this time.[21] Former Pittsburgh Steelers receiver and current NBC Sports analyst Hines Ward stated the use of the system would be "opening a Pandora's Box," and that the data recorded by the system could be used by team owners to give players lower salaries.[20]

In November 2011, the Cleveland Clinic Center for Spine Health created an online study released by the Journal of Neurosurgery in which various football helmets were compared with each other via crash test dummies. It was also found that leather helmets provided similar results to modern helmets, and in some cases, the leather helmets proved to have superior protection against concussive blows. However, the leather helmets did not provide as much protection against skull fractures.[22][23][24]

Federal NFL Concussion Litigation[edit]

In April 2011, attorneys Sol H. Weiss and Larry E. Coben from the Philadelphia law firm of Anapol Schwartz filed a federal lawsuit on behalf of Ray Easterling, Jim McMahon and five other players. Thousands of former NFL players have since filed lawsuits against the League after suffering repeated concussions throughout their careers.

The multidistrict litigation (MDL) titled In re: National Football League Players' Concussion Injury Litigation (MDL 2323) was filed on January 31, 2012 in the United States District Court for the Eastern District of Pennsylvania. Judge Anita B. Brody presides over the matter.[25] The master administrative long-form complaint, filed by Plaintiff's Co-Lead Counsel Sol Weiss and Christopher Seeger on June 7, 2012, alleges the League "... was aware of the evidence and the risks associated with repetitive traumatic brain injuries virtually at the inception, but deliberately ignored and actively concealed the information from the Plaintiffs and all others who participated in organized football at all levels." The master complaint argues the NFL knew or should have known players who sustain repetitive head injuries are at risk of suffering "... early-onset of Alzheimer's Disease, dementia, depression, deficits in cognitive functioning, reduced processing speed, attention, and reasoning, loss of memory, sleeplessness, moods swings, personality changes, and the debilitating and latent disease known as Chronic traumatic encephalopathy ('CTE')."[26]

In April 2012, Easterling was found dead from a self-inflicted gunshot wound in his home.[27] An autopsy report concluded Easterling's brain had evidence of CTE, a degenerative brain disease associated with frequent blows to the head.[28]

One month later, former San Diego Chargers player Junior Seau also died of a self-inflicted gunshot wound, and a brain autopsy showed he suffered from CTE.[29]

Like Easterling and Seau, an autopsy of Bears safety Dave Duerson's brain after he committed suicide earlier that year revealed he also suffered from the same degenerative brain disease.[30]

The autopsy results following these players' suicides heightened existing concerns regarding the connection between player deaths and concussions. Neurosurgeon Julian Bailes has identified CTE in the autopsies of former players Mike Webster, Terry Long, Justin Strzelczyk, Andre Waters, and Chris Henry.[31][32] One of the difficult issues facing doctors is attempting to identify mental health effects from concussions during the lives of former players rather than after their deaths.[33] In April 2012, a group of former Dallas Cowboys—including Pro Football Hall of Fame inductees Randy White, Bob Lilly, and Rayfield Wright (among other retired players from around the league)—filed a lawsuit against the NFL, again accusing it of ignoring a link between concussions and brain injury.[34]

In August 2012, the number of players involved in suits against the NFL increased to 3,402, and the League sued three dozen insurance companies in an attempt to force them to cover the costs of defending claims of not protecting players. However, Travelers ultimately sued the League on August 21 in a lawsuit called Discover Property & Casualty Co. et al. vs. National Football League et al., New York State Supreme Court, New York County, No. 652933/2012. The company provided liability coverage for the League's merchandising arm (NFL Properties), and the insurer also pointed out that the above mentioned lawsuit has allegedly 14 counts against the League, while only two against NFL Properties.[35]

After quarterbacks Jay Cutler, Michael Vick and Alex Smith sustained concussions in Week 10 of the 2012 season, the National Football League Players Association (NFLPA) reiterated their plans to have independent neurologists on the sidelines at every game.[36] The 2013-14 NFL season involved an independent neurological consultant per team on the sideline of every game.[37] Concussion guidelines released by the NFL in 2013, mandated a four-stage protocol for concussions, including examinations, treatment and monitoring prior to a return to play.[38][39][40] In March 2013, the League proposed a rule to reduce concussions by making it illegal for a ball carrier or tackler to "initiate forcible contact by delivering a blow with the top crown of his helmet against an opponent when both players are clearly outside of the tackle box." However, the proposal was met with criticism from players like running backs Matt Forte, Emmitt Smith and Marshall Faulk.[41]

A federal hearing was held on April 9, 2013 in Philadelphia to discuss the League's motion to dismiss the lawsuits brought on behalf of more than 4,500 former players On July 8, 2013, Judge Brody ordered representatives of both sides of the litigation to explore a possible settlement in the litigation. Judge Brody ordered a report on or before September 3, 2013 regarding the results of the mediation.[42]

A proposed settlement was reached in the litigation on August 29, 2013. Under the agreement, the NFL will contribute $765 million to provide medical help to more than 18,000 former players. Retired players who suffer severe neurological conditions such as Alzheimer's and amyotrophic lateral sclerosis (ALS) diseases in the future will also be eligible to apply for medical help. In addition, $10 million will fund brain injury research as well as safety and education programs.[43]

The settlement says it should not be interpreted as a statement of legal liability on the part of the NFL.[44]

The settlement, which is projected to protect retired players for nearly 65 years, will compensate injured former players who need immediate help and will provide baseline assessments and medical benefits to those who are symptom-free or beginning to show signs of neurological problems.

"I think it's more important that the players have finality, that they're vindicated, and that as soon as the court approves the settlement they can begin to get screening, and those that are injured can get their compensation. I think that's more important than looking at some documents," attorney Weiss said.[45]

Kansas City Chiefs concussion lawsuit[edit]

On December 3, 2013, 5 former NFL players filed a lawsuit against the Kansas City Chiefs organization: former Chiefs players Alexander Cooper, Leonard Griffin, Christopher Martin, Joe Phillips, and Kevin Porter. They wish to know what the Chiefs knew about concussions and when they knew it.

"I would like to have had the opportunity to know that going back on the field (after concussions) would cause me to have severe disabilities later in life ..." said Chris Martin, a former Kansas City Chiefs Linebacker.[46]

This lawsuit is unique and different from the thousands of lawsuits previously filed against the NFL. These players are not suing the NFL, and are instead suing the Chiefs.

From 1987 to 1993 there was no Collective Bargaining Agreement established in the NFL. With no existence of a CBA in these years, players who played during this time for the Chiefs can sue the team for many of the same reasons the NFL has been sued. The $765 million settlement in August 2013 between the NFL and former players only protected the NFL. "I think all of our clients were disappointed," McClain said of his clients reaction to the settlement with the NFL.[47] The players currently suing the Chiefs have all opted-out of the settlement from the previous mediation with the NFL.

A law unique to Missouri allows certain former NFL players to sue the individual team. The current Missouri law states that employees can sue employers in civil court if the employees declined worker's compensation. The Independence attorney for the five ex-Chiefs, Ken McClain said, "The lawsuit is allowed in Missouri after a state workers' compensation statute was amended in 2005 to exclude cases of occupational injury that occur over an extended time."[48]

The amendment of the 2005 law is set to be changed at the end of December 2013. Martin and McClain have both encouraged former players who are eligible to join the lawsuit before the their window of opportunity expires.

Concussions in college football[edit]

The NCAA, like the NFL, has been criticized for its handling of concussions, with numerous players having retired from football due to concussions, or have filed lawsuits against the association for failing to protect student-athletes from concussions.[49] In 2011, former players Derek Owens and Alex Rucks filed lawsuits against the association for failing to cover the players' safety. Both Owens and Rucks claimed that they had suffered brain trauma which could have been prevented.[50] In 2012, the Southeastern Conference and Big Ten Conference began work on preventing concussions, and appointed University of Mississippi Chancellor Dan Jones to evaluate and review existing research and various diagnoses from past analyses.[51] In 2009, an NCAA panel created and recommended a rule that prevents an athlete from returning to a game after he/she has sustained a concussion. The panel also had recommended for an athlete to be sidelined after any concussion-related injury until he/she has been cleared by a doctor.[52]

"There's been less focus on college players who don't go on to play professional sports, but I think you'll see that getting more attention and go down to people who play it at every level. From time to time we have all had concerns of what we ask student-athletes to do and what the long-term health may be."[53]

—University of Mississippi Chancellor Dan Jones

Concussions in other leagues[edit]

Canadian Football League[edit]

In the 2010 season for the Canadian Football League, there have been 50 reported concussions; 44.8 percent of players reported having a concussion or concussion-like symptoms, 16.9 percent had confirmed that they had a concussion, and 69.6 percent of all players who suffered from concussions that year suffered from more than one.[54] However, the average of 0.59 concussions per game is lower than the 0.67 recorded by the NFL in 2010.[55] The league eventually started a concussion-awareness program with the help of Football Canada, Canadian Interuniversity Sport (CIS), the Canadian School Sport Federation, the Canadian Football League Players Association (CFLPA), the Canadian Football League Alumni Association (CFLAA), and the ThinkFirst program.[56] The league eventually pointed out eight protocols:[57]

  • Team physicians and therapists are to use a SCAT2 (a medical protocol), to diagnose concussions and preventing athletes from playing until they have been cleared to play.
  • All players are to be submitted to IMPACT, which is a form of cognitive testing, during training camp.
  • All player concussion assessments in the CFL are to only be used by team physicians and therapists.
  • All coaches and players will receive educational items to aid in recognizing signs of a concussion.
  • Administrators are to report a change from the expectation that a player returns to the game to one that encourages players to be honest about symptoms.
  • The formation of certification programs that teach coaches how to recognize the symptoms of concussions.
  • The formation of training programs for coaches that emphasize that players should never use their helmets to tackle.
  • A new rule in the amateur football rulebook was implemented that requires officials to report suspected concussed players to the coaching or medical staff during games.

In 2012, ThinkFirst founder and Toronto Western Hospital neurosurgeon Charles Tator led a study that was conducted by the University of Toronto, which examined the brains of 20 former players with a history of concussions, and compared them to 20 other players without a history of head injury. A separate group of 20 without football experience served as a control group. Also in 2012, the league and Tator announced a partnership to work in a study that would perform postmortem tests on former CFL players to look for signs of CTE.[58]

Arena Football League[edit]

In the Arena Football League, despite the league's intense play, very few lawsuits have been filed for concussions. The most notable lawsuit against the league was a lawsuit filed by former Colorado Crush kicker Clay Rush in 2010, who claimed that he suffered from permanent brain damage due to repeated blows to the head during games.[59] Like the NFL, the AFL prohibits players who suffered from concussions from practicing.[60] In 2008, during the original league's final season, the "Shockometer" made its debut at two season-opening games (Dallas Desperados vs. Georgia Force/San Jose SaberCats vs. Chicago Rush) on 40 player helmets. The device is projected to sell for $30 if it is to become available on the market.[61] The players that were given the device play positions that are suspectible to hard hits, such as wide receivers, defensive backs, running backs and linebackers. AFL Players Association regional director James Guidry stated that the red light doesn't mean that the player has a concussion, but as a warning for team examiners to inspect the player. Guidry also said that the device could be used to prevent players who don't want to show any signs of weakness after sustaining any concussion-like symptoms from continuing to play.[62]

"What happens in a game is much different than what happens in lab situations. To be able to have a partner like the AFL that values this project as much as we do is fantastic. We can learn an awful lot and make this product as good as it can be before it's winding up on the field in widespread use."[61]

—Dave Rossi of Schutt Sports on the Shockometer

Youth football[edit]

Youth athletes make up 70% of football players in the United States. One of the first studies of its kind was performed during the Fall 2011 football season when researchers from Virginia Tech, receiving permission from parents, placed accelerometers (which measure g forces) inside the helmets of seven youth players. These seven players were 7- and 8-year-old boys participating in a community youth league who were chosen because they were expected to have high participation and also because they wore at least a youth medium Riddell Revolution helmet (enabling the accelerometers, battery, and wireless transmitter to fit inside the helmet between the padding). That is, these seven were not a random selecting of players. Rather, the purpose of this study was to establish a baseline of what range of hits are generally expected.[63]

As way of comparison, a collision of 80g is a big hit in a college football game of which there might be only six per game. And the range of 80, 90, or 100g is generally where risk of acute injury and concussion begins to occur (concussion being symptoms such as feeling foggy or woozy and not necessarily loss of consciousness). An example of a lesser force of 40g is heading a soccer ball, and even with blows in this 30 to 40g range, it is not known whether these pose a cumulative risk of injury.[63]

This 2011 study measured a total 753 impacts among these seven players with a median impact of 15g. It did, however, observe 38 impacts of 40g or greater, and six impacts of greater than 80g. Fortunately, none of these youth players experienced a concussion. There is also a concern that since many young players have less developed chest and neck muscles than older players, almost every impact potentially acts likes a surprise hit.[63]

A Virginia Tech doctor stated that reducing the number of higher hits during practice sessions constitutes a real opportunity. Of the 38 impacts of 40g or greater, 29 took place during practice. And of the six impacts greater than 80g, all took place during practice.[63]

Concussions in high school football[edit]

Concussions are prevalent in high school football. About 50 high school or younger football players across the country were killed or sustained serious head injuries on the field since 1997.[64]

A 2013 study by Cincinnati Children's Hospital Medical Center found that despite knowing the risk of serious injury from continuing to play with a concussion, half of high school football players would still play if they had a headache from an injury sustained on the field. Researchers surveyed 120 high school football players. Of those students, 30 reported having suffered a concussion. More than 90 percent recognized the risk of serious injury if they returned to play too quickly, but more than half of those aware of the risks responded they would "always or sometimes continue to play with a headache sustained from an injury," and only 54 percent indicated they would "always or sometimes report symptoms of a concussion to their coach."[65]

Prevention efforts[edit]

Numerous efforts have been attempted to prevent concussions, such as a device created by Schutt Sports during the Arena Football League's 2008 season known as the "Shockometer"—a triangle-shaped object with adhesive on its side that sticks to players' helmets. When a player gets hit by a g-force which exceeds 98, a capsule with a green light in it will change to a red light. Doctors have determined that a g-force of approximately 100 will increase the risk of a concussion, even though a quarterback that gets sacked would normally register a g-force of 150 g. A possible flaw to the Shockometer is that fan activity could accidentally trigger the device.[66] Riddell created the Head Impact Telemetry System (HITS) and Sideline Response System (SRS) to help record the frequency and severity of player impacts during practices and games. Every HITS helmet features MX Encoders, which would automatically record every hit.[67] Eight NFL teams had planned to use the system in the 2010 season, but it was ultimately not used.[20] In 2013, Reebok developed the Head Impact Indicator, which is a quarter-sized device placed on a player's skull, which activates a red/yellow light if the player is hit too hard.[68] Similarly to Reebok's Impact Indicator, Battle Sport Science has released the Impact Indicator 2.0. The Impact Indicator 2.0 looks to increase long-term brain safety for all those who play football.[69] On February 3, 2013, the NFL and General Electric partnered on a five-year, $50 million project to develop technology to predict brain injuries, show injury severity and the rate of recovery, and to create more protective material.[70]

Screening Procedures[edit]

To date, all screening procedures that examine football players for brain damage have been post mortem. In 2013, Dr. Gary Small and colleagues developed an in vivo chemical tracer that can detect tau protein build up in living players. Dr. Small and his team invented this new chemical tracer, 2-(1-{6-[(2-[F-18]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile, or FDDNP, that could be used in positron emission tomography (PET).[71] This new tracer measures for tau protein and amyloid plaque accumulation in human brains; symptoms of repetitive brain trauma among other things. Although tracers have been developed to screen for the build-up of tau proteins in the human brain, FDDNP is the first PET tracer that can be used in vivo in human trails. FDDNP was originally developed in an effort to detect Alzheimer’s in elderly individuals, thus the article was published in the journal of the American Association for Geriatric Psychiatry. However, because there are similarities between Alzheimer’s and the effects of chronic traumatic encephelopathy (CTE), FDDNP was used to study the extent of brain trauma in consenting, retired NFL players.

Dr. Small and colleagues performed a controlled experiment on retired NFL players and an equal number of control participants. Unfortunately the sample size was very small as only 5 players of the 19 contacted were eligible for the study. Though the sample size was small, a good range of positions were represented (linebacker, quarterback, offensive lineman, defensive lineman, and a center) and all players had played in the league at least 10 years. The players had to be at least 45 years of age and currently exhibit symptoms of cognitive and mood disruption. Control participants had to meet certain criteria as well to ensure that they were as similar as possible to the NFL players in order to eliminate any biases or confounding variables. Age, Body Mass Index (BMI), years of education, and family history of dementia were all selected as the selection criteria for control participants. All participants received intravenous injections of the FDDNP tracer and were tested over 4 weeks using PET imaging technology.

The injection of the FDDNP tracer was successful, and the results of the study showed significant differences between the NFL players and control participants. The NFL players had significantly higher FDDNP signals than control participants, indicating a greater amount of tau protein accumulation. The cortical regions of all the participants studied showed no significant difference, but the NFL players had FDDNP levels that were significantly higher in the caudate, putamen, thalamus, sub thalamus, midbrain, and cerebellar white matter regions of the brain as compared to the control participants.[71] In addition, a positive correlation was found between the number of head injuries the players sustained and the levels of FDDNP binding. This suggests that players with a more severe history of head trauma will likely have significantly more accumulation of tau protein. This, in turn, gives rise to the suggestion that a more sever history of head trauma will result in greater deterioration of the brain, cognitive functioning, and mood regulation.

The findings of the study were consistent with previous autopsy studies of individuals with CTE. The important distinction to make, however, is that the patients in Dr. Small’s study were not on the slab and walked out after testing was completed. This is monumental in the field of brain trauma and concussion research.

Recovery efforts[edit]

Concussions are proven to cause loss of brain functioning that can lead to physical and emotional symptoms, attention disorders, depression, headaches, nausea, and amnesia. These symptoms can last for days or week and even after the symptoms have gone, the brain still won't be completely normal. Players with multiple concussions can have drastically worsened symptoms and exponentially increased recovery time.

Researchers at UCLA have for the first time used a brain-imaging tool to identify a certain protein found in five retired NFL players. The presence and accumulation of tau proteins found in the five living players, are associated with Alzheimer's disease. Previously, this type of exam could only be performed with an autopsy. Scientists at UCLA created a chemical marker that binds to the abnormal proteins and they are able to view this with Positron Emission Tomography (PET) scan. Researcher at UCLA, Gary Small explains, "Providing a non-invasive method for early detection is a critical first step in developing interventions to prevent symptom onset and progression in CTE".[72]

Information[edit]

See also[edit]

Further reading[edit]

References[edit]

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  2. ^ a b c Peter, Peter. "Elliot Pellman, the NFL's top medical adviser, claims it's okay for players with concussions to get back in the game. Time for a second choice". ESPN Sports. Retrieved 2013-09-03. 
  3. ^ "Concussion in professional football: helmet testing to assess impact performance--part 11.". United States Public Health Service Centers for Disease Control and Prevention National Institute for Occupational Safety and Health. 2004-01-10. Retrieved 2013-09-03. 
  4. ^ "Concussion in professional football: helmet testing to assess impact performance--part 11.". Mild Traumatic Brain Injury Committee, National Football League. January 2006. Retrieved 2013-09-03. 
  5. ^ "The management of concussion in sports (summary statement)". Neurology Journal. March 1997. Retrieved 2013-09-03. 
  6. ^ "Concussion in professional football: players returning to the same game--part 7.". University of North Carolina, Chapel Hill, North Carolina. Retrieved 2013-09-03. 
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  8. ^ Brady, Don (2004). A Preliminary Investigation of Active and Retired NFL Players’ Knowledge of Concussions (Ph.D.). The Union Institute and University. 
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Brand and Age of Football Helmets Make No Difference in Concussions

External links[edit]