MARINA DEL REY, Calif. (AP) _ An estimated 350,000 athletes endure some kind of head injury while playing sports every year in the United States, and that's only counting the ones who lose consciousness after impact.
Counting the rest of the dings, pings and ``rung bells'' that result in concussions, the total could be as high as 3.8 million.
That's why concussions are, in the words of agent Leigh Steinberg, ``a health epidemic, the consequences of which are a ticking time bomb that may not be seen in their totality for 10, 15 or 20 years.''
Steinberg and NFL Hall of Fame quarterback Warren Moon, who suffered the first of his half-dozen concussions at age 11, headlined a summit Friday designed to draw attention to the growing problem of concussions in sports.
It's a problem most widely recognized in the NFL, where the suicide of former defensive back Andre Waters and the story of former Patriots linebacker Ted Johnson's hurried return to the field made recent headlines.
But the issue has repercussions in almost every sport, at almost every level.
``A lot of parents aren't aware of what concussions are and what the severity is,'' Moon said. ``My first concussion didn't necessarily come from a collision. It came from my head slamming against the infield where we practiced on a baseball diamond.''
Indeed, determining the cause of concussions and both the immediate and long-term effects they have is a constantly shifting science.
Steinberg touted numbers from a series of recent studies, hoping the gravity of the new stats will intensify the debate and bring quicker change.
``What are the stakes?'' Steinberg said. ``It's one thing to go out and play football and understand that when you turn 40, you can bend over to pick up your child and have aches and pains. It's another thing to bend down and not be able to identify that child.''
One study showed that athletes are six times more likely to suffer a second concussion if they return within a week of the first one. A client of Steinberg's, former 49ers quarterback Steve Young, retired after precisely that kind of quick return and repeat injury.
Other studies showed that in cases where athletes had three or more concussions over their lifetime, they were five times more at risk for early onset Alzheimer's disease, three times more at risk of significant memory loss and four times more likely to have severely elevated depression.
The NFL and the NFL Players Association have done some things to lessen the impact of head injuries _ most notably with rules changes and the gradual elimination of Astroturf as a playing surface. They're looking at changes in helmets and mouthpieces to lessen the severity of hits to the head.
Steinberg some day also would like to see neurologists present on every NFL sideline and more effective use of baseline tests that establish players' capabilities before they get injured and can be used as good markers for the tests they take after concussions.
Not as easily changed is the football player mentality. From a young age, they're taught to play in pain, to sacrifice their bodies, to stay on the field and to make their coaches happy.
``Most athletes are in a state of denial,'' Steinberg said. ``They're taught to ignore pain.''
He hopes some of the most recent studies will lead NFL management to conclude that rushing players back isn't in anyone's best interest. After all, is getting a player back for one week worth risking him for the rest of the season _ or his career? It's a question that has gained more traction as salaries and signing bonuses have exploded over the past decade.
Almost as difficult as changing the mind-set simply is determining what is or isn't a concussion, which would translate into determining the kind of medical attention these players receive.
To illustrate this challenge, one doctor showed two plays from a recent Oregon-Arizona college football game. One showed a player's helmet getting popped off after a particularly vicious hit made under his chin. Another showed one player knocking his teammate to the ground in a congratulatory body bump after a good defensive play.
The player in the first example walked away with a cut lip. The player in the second example had a concussion because his head banged against the turf as he received the congrats.
``It goes to show that we can be fooled by what we see,'' said Kevin Guskiewicz, a specialist from the University of North Carolina who studies the biomechanics of sports concussions.