An expert committee of clinicians and researchers today called for an end to most types of bodychecking, a collision tactic, in youth ice hockey, and backed other changes for preventing and treating sports-related concussions. But the international panel offered no resolution to an especially controversial question in professional sports—the extent to which repetitive head injuries cause brain disease later in life—instead saying rigorous cohort studies are needed to prove a causal relationship.

“We need … much better designed case control and cohort studies that include most importantly, careful control of the confounding variables,” said Robert Cantu, a neurosurgeon at Boston University School of Medicine and a co-author of a systematic review that addresses the question. Those conclusions drew fire from outside researchers who say the panel ignored compelling evidence that establishes a causal link.

The panel, Concussion in Sport Group (CISG), funded by the International Olympic Committee and other international sports federations, periodically conducts systematic literature reviews to inform consensus statements that influence physicians and other practitioners worldwide. The group’s sixth consensus statement, published today in the British Journal of Sports Medicine, recommends banning bodychecking (a hit by a defensive player on a player carrying the puck) in most youth ice hockey and backing universal mouthguards in children and adolescents in the sport. (Its systematic review of prevention measures found that bans on bodychecking in youth hockey reduced the rate of concussions by 58%.) The report also called for broadening the use of warmup neuromuscular training exercises that have reduced concussions in rugby and limiting contact practice in U.S. football at all levels.

The 31 co-authors, drawing on literature reviews assisted by 70 others, also conclude that the standard prescription of strict rest and bans on screen time for days after a sport-related concussion may not be beneficial. They advise that supervised activity such as walking or stationary cycling should begin immediately and limited screen time should be allowed in the first 2 days, unless any of these cause significantly worse symptoms.

“The main message [is]: ‘Don’t cocoon,’” said John Leddy, a co-author who directs the concussion management clinic at the University at Buffalo, at a press conference yesterday. The prior advice, he said, was based on animal research and “expert opinion.” But, “New evidence … is now quite strong and based upon randomized controlled trials in humans showing that in fact, doing that does not help recovery. It probably actually delays recovery.”

Members of the panel and outside experts also compiled a systematic review on the long-term health effects of repeated sport-related concussions, analyzing their links to diseases including dementia, amyotrophic lateral sclerosis, and Parkinson’s disease as well as the neurodegenerative disease known as chronic traumatic encephalopathy (CTE). They concluded that no causative links have been established, although they acknowledged that CTE is “potentially associated” with repetitive head injuries in sport.

“The studies that we reviewed have some pretty significant methodological limitations … because they could not control for or examine factors that we know are important when we’re looking at later in life problems with brain health, like genetics, your level of education, your socioeconomic status, hypertension, and cardiovascular disease,” said lead author Grant Iverson, a neuropsychologist at Massachusetts General Hospital and Harvard Medical School.

But some epidemiologists note that the panel excluded a large literature of case studies such as those arising from brains of former professional athletes housed in a bank at Boston University. They also say no plausible confounders have been proposed.

“Confounding only occurs when some variable is both a cause of disease and is associated with the exposure you’re studying,” says Adam Finkel, an environmental risk assessor at the University of Michigan School of Public Health. In the case of CTE and repeated concussions, he says, a confounding variable would have to be both toxic to the brain and something that football players were exposed to far more than others—like a brand of locker room soap that only National Football League (NFL) players use.

Finkel, a former chief scientist at the U.S. Occupational Safety and Health Administration, added: “These guys won’t accept case reports, basic epidemiology, animal models. They are waiting for the prospective cohort study that will either never happen or happen after they are gone,” because it requires following players and nonplayers for decades. Finkel and colleagues including Cantu last year concluded from a literature assessment that there’s convincing evidence that repetitive head impacts cause CTE.

Although many CISG panelists are academic experts, many have been, or currently are, volunteer or paid consultants for sports organizations including NFL and FIFA, professional soccer’s international governing body. Others currently work for the National Collegiate Athletic Association, the National Hockey League, and Major League Soccer.

CISG has in the past been criticized for a lack of transparency in its consensus statement process. In the current report, unlike past ones, votes were anonymous—80% was needed for consensus—but dissenting opinions were included in the statement, as were extensive financial disclosures.

Those measures did not satisfy Willie Stewart, a neuroscientist who studies traumatic brain injury at the University of Glasgow and who tweeted critically today. He says that the panel’s process was flawed because it gave equal voting weight to panelists who were nonspecialists in the topic at hand. For instance, he says of the lopsided, 27-to-two vote approving the text on long-term neurological impacts, “How many of those admitted nonexpert[s] … simply agree[d] with … the summary text provided by the lead reviewer? This is where it becomes an echo chamber, and not a valid consensus—by any stretch.” He added that on these grounds alone, “Any editor should have rejected the draft [consensus statement] as fundamentally flawed.”

The panel has also taken heat for lacking diverse representation of disciplines and experience, including patients or family members. Many panel members are sports medicine physicians and other medical specialists who treat patients, as opposed to public health experts like epidemiologists and biostatisticians who look at populations.

The group’s statement did not address the issue of diversity of expertise, but it acknowledged needing greater demographic and geographical diversity: South Africa was the only non–Northern Hemisphere country represented; six of 31 members were women; two were nonwhite; and one was a former Paralympic athlete. And panelists acknowledged a stark lack of content addressing women in sport, because they are not represented in the literature. For instance, no women were included in the research that was assessed for the systematic review of long-term neurological disease.

“A challenge is that a lot of the literature is not focused on female athletes,” explained Kathryn Schneider, the consensus group’s co-chair and a physiotherapist at the Sport Injury Prevention Research Centre at the University of Calgary. “This is an important consideration for the future.”

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