But a study published Tuesday in the American Journal of Sports Medicine provides a look at how the brain and sports performance still may be affected after the most obvious symptoms of concussion have cleared, raising questions about whether athletes -- at all levels -- are truly recovered when we send them back on the field.
The research looked at professionals' ability to hit a baseball -- one of the most difficult skills in sports -- after returning from a concussion. Hitting requires remarkable vision, reaction time and hand-eye coordination, and every at-bat can be measured in a number of ways.
When the researchers from the University of Rochester compared 66 batters who were cleared to resume play after a concussion with 68 who took similar time off for the birth of a child or a death, they found that the concussed group had much more trouble hitting. In the two weeks after re-taking the field, they had lower batting averages (.235 vs .266), on-base percentages (.294 vs .326), slugging percentages (.361 vs .423), and on-base plus slugging percentages (.650 vs .749).
The good news is that the gap between the two groups closed within four to six weeks after the athletes took time off, though the concussed players still showed slightly poorer performance.
"Our findings suggest that concussed baseball players who are cleared to return to play through traditional approaches may not have fully returned to baseline status before their return," the authors wrote. Under Major League Baseball policy, a club must certify that all of a player's concussion symptoms have disappeared and that his results on a standardized screening test have returned to pre-concussion levels.
"The more we look at it, the more we see that the brain takes a long time to heal," said Jeff Bazarian, a professor of emergency medicine at the University of Rochester, who led the study. "The good news is it does heal."
Research and anecdotal reports have long indicated that symptoms such as slowed thinking and response, fogginess, poor concentration, attention deficits, slower information processing speed, poorer balance and problems with eye movement can linger for weeks or months after a concussion. Yet, if cleared on screening tests, a player can return to the field in many sports and risk another dangerous blow to the head.
Bazarian believes that hitting a baseball is so complex and difficult -- at the Major League level, hitters have four-tenths of a second to do it -- that the performance decline may signal ongoing problems that current tests do not. "Baseball uncovers that weakness because it's such a difficult thing to do," he said.
According to the researchers, this is the first study to look at the performance of baseball players after a concussion. To allow a fair comparison, they controlled for numerous factors and looked at both groups' pre- and post-event performance. "The rust factor is not at play here," Bazarian said. "[The concussed hitters'] performance is not worse because they were rusty."
Interestingly, hitters who suffered concussions struck out and walked at about the same rate as those who took time off, suggesting that they did not have trouble seeing the ball. But the study suggests that lingering concussion symptoms may affect a batter's timing just enough to diminish power and control of the bat.
"I think we need to know more about what we're doing when we clear people," Bazarian said. "They're clearly not recovered."