Some scientists studying the relationship between contact sports and memory or mood problems later in life argue that cumulative exposure to hits that cause a snap of the head — not an athlete’s number of concussions — is the most important risk factor.
A hit was defined as an impact causing 10 times gravitational acceleration — that is, a snap of the head more forceful than one produced by, say, jumping. Those hits included blows not directly to the head.
The greater the number in a career, the higher the likelihood of problems later in life. The cumulative number of hits was also a better predictor of later-life impairments than other measures, such as a player’s concussion total or the age when he began playing, the study found.
“I think of the study as just the beginning of trying to characterize exposure in a more precise way,” said Michael McClean, a Boston University public health researcher and one of the authors of the paper.