Hits and checks have long been accepted as inherent to the game of hockey, but a decision by the NHL's biggest star to sit out of the game indefinitely represents only the latest professional athlete to suffer lasting injuries to the brain.
Sidney Crosby last week cited lingering concussion-like symptoms from at least one blow to the head that left him out of the game for 10 months.
"I've got to make sure with these sort of things that I'm careful and aware and making sure I'm 100 percent before I come back," Crosby, 24, told reporters in Pittsburgh last Monday. "You've got to listen to your body on these things."
Frustrated with the long-term risk of these sports, one neurologist, along with many others in agreement, called for a ban on intentional hitting and fighting in the game of hockey.
Dr. Rajendra Kale, neurologist and interim editor-in-chief of the journal CMAJ, published an editorial today that cites several athletes who experienced repetitive blows to the head during contact sports. Such hits led to severe medical problems, including short-term and long-term memory loss, chronic headaches, sleep disorders, mood and behavioral problems, psychiatric changes and even early onset dementia.
"When you find any tradition is causing damage to human's brain, it's time to change traditions," Kale told ABCNews.com. "We found traditions that are harmful and we need to give them up."
Symptoms of concussions include headache, nausea, confusion and loss of memory. Lingering effects can last for days, weeks or months, depending on the severity of the blow.
While Kale noted in the editorial that he was fascinated by the skill, grace and physical fitness needed to play hockey, he "was appalled by the disgraceful and uncivilized practice of fighting and causing intentional head trauma. The tragic story of Sidney Crosby's layoff due to concussions has not been sufficient for society to hang its head in shame and stop violent play immediately."
Kale cited three other hockey players -- Rick Martin, Reggie Fleming and Bob Probert -- who have been diagnosed with chronic traumatic encephalophy, or CTE, a progressive degenerative disease found in people who have sustained several concussions or other head injuries.
As a native Canadian, Dr. Lyn Turkstra, professor in the department of neurological surgery at University of Wisconsin-Madison School of Medicine, said there is still much to learn about how to best protect athletes in contact sports.
"I grew up with hockey fights and appreciate that blood sports are a part of our collective culture," Turkstra said. "So is exceptional puck-handling, however, which would be more evident if players spent less time with their gloves off. It's good to remember that helmets and mouth-guards also were highly controversial when implemented in sports, and perhaps the same was true for hockey pads in the early 20th century, but most players would feel dangerously exposed without any protection today."
Blows to the head and body cause a series of changes in the brain, including mechanical injuries to brain cells and their connections, stress on cells that are not receiving enough oxygen, and, in more severe cases, damage to specific regions to the brain that are next to sharp interior surfaces of the skull, Turkstra explained. The brain seems to be able to recover from mild disruptions in function, if given enough time to heal, but at some point, the brain can no longer adjust to compensate for such stressors.
"We don't know what that magic threshold is, and also don't yet know why some people seem more vulnerable than others," Turkstra said.
"I'm concerned that these new findings are just the tip of the iceberg," said Dr. Christopher Giza, associate professor of pediatric neurology at UCLA and member of the American Academy of Neurology. "There are studies that show the longer you have a career in contact sports, the higher a person is at risk for chronic impairment. It's worrisome whenever you see a dose response like that."
Despite the many unknown variables, scientists have found that "brain rest" after any force has been applied to it, including direct contact to the head, but also body blows that cause the brain to move about within the skull, has shown some improvement in long-term outcomes.
Players should always wear proper equipments, experts said, and unnecessary hits and fighting should be penalized with heavier fines and regulations. If players get their "bell rung," coaches should take them out of the game immediately to be evaluated.
More than 500 professional athletes agreed this fall to donate their brains to science, a move that scientists hope will allow for a better understanding of the progressive brain diseases associated with professional athletes who play contact sports.
While studying the brains of contact-sport athletes is important, Giza said, the sample should also be expanded to all contact-sport athletes, to compare the seemingly healthier players with those who experience more adverse effects.
"One concussion is one too many," neurologist Kale said. "Hockey is a beautiful game, but it is spoiled and marred by these fights, hits and subsequent danger and damage to the brain."