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. That possibility is particularly worrisome in football, in which frequent “subconcussive” blows are unavoidable.
On Thursday, researchers based atBoston University reported the most rigorous evidence to date that overall exposure to contact in former high school and college football players could predict their likelihood of experiencing problems like depression, apathy or memory lossyears later.
The finding, appearing in The Journal of Neurotrauma, is not conclusive, the authors wrote. Such mental problems can stem from a variety of factors in any long life.
Yet the paper represents researchers’ first attempt to precisely calculate cumulative lifetime exposure to contact in living players, experts said. Previous estimates had relied in part on former players’ memories of concussions, or number of years played. The new paper uses more objective measures, including data from helmet accelerometer studies, and provides a glimpse of where the debate over the risk of contact sports may next play out, the experts said.
“They used a much more refined and quantitative approach to estimate exposure than I’ve seen in this area,” said John Meeker, a professor of environmental health sciences at the University of Michigan School of Public Health, who was not a part of the research team. But he added, “Their methods will have to be validated in much larger studies; this is very much a preliminary finding.”
The study did not address the risk of chronic traumatic encephalopathy, or C.T.E., a degenerative scarring in the brain tied to head blows, which can be diagnosed only after death.
The Boston team estimated overall exposure to contact in 93 former high school and college players ages 24 to 82. The estimate was based on the number of seasons played; at which position; and the average number of hits expected for that position, at each level of play, beginning in youth leagues.
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 researchers used data from helmet accelerometer studies to estimate the average number of these hits per position. For example, a college linebacker might have 685 impacts per season, and a college quarterback closer to 200.
Those hits added up, the researchers found: 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.
Robert Stern, another of the authors, said: “We do not want to imply that the numbers or thresholds in this paper should be used to evaluate risk for any individual athlete. We’re going to need much larger studies to get numbers that are meaningful.”