1 concussion + CTE
 

"Boston University researchers have found a degenerative disease linked to head trauma in the brain tissue of the late NHL great Rick Martin, the first 50-goal scorer for the Buffalo Sabres and a member of their famed French Connection line."

Rick Martin had only one diagnosed concussion and they found CTE in his autopsied brain. Scary stuff.

http://www.cbc.ca/sports/hockey/nhl/...-national.html

If you read the full research on CTE, one of the biggest causes is Sub-Concussive Impacts. Hockey players suffer many sub-concussive impacts in each game. Since there are no symptoms from these impacts, they do nothing to let the brain heal.

The research done at UNC-Chapel Hill shows that football players receive 700 to 900 sub-concussive impacts PER SEASON. These many mild shakings of the brain combine to cause CTE.

fyi, CTE is Chronic Traumatic Encephalopathy, defined as a shrinking or atrophying of the brain.