The director of the Canadian Concussion Centre at Toronto Western Hospital says when it comes to the number of acknowledged concussions, you can usually double the total for athletes who participate in collision sports.
That is not good news for Pittsburgh Penguins captain Sidney Crosby, who suffered what is believed to be the fourth concussion of his NHL career on Monday night.
Neurosurgeon Dr. Charles Tator says when someone has suffered multiple concussions, the chance of having persisting symptoms "goes up terrifically."
He notes that athletes may experience the sensation of seeing stars or might take knocks to the head at the youth level but don't acknowledge them as head injuries.
Tator says a concern for Crosby to consider at this point is the likelihood of a full recovery, since the chances of that go down as the number of concussions goes up.
He also says the fact that Crosby needed almost a year to recover from a concussion in early 2011 means there was a significant, residual effect on his brain. Tator adds that if Crosby were an amateur, he would probably be advised to quit the sport.