If Michael Waltrip were to count up all the concussions he has sustained over a NASCAR career that stretches back nearly 30 years, he'd certainly hit 10 - and probably keep going.
Safety measures since Dale Earnhardt's death in 2001 have gone a long way toward preventing head injuries, and NASCAR officials have taken steps to improve the way they identify and treat concussions. But Waltrip knows that won't undo all those hits he took in the 1980s and '90s.
''I whacked my head - a lot,'' Waltrip said. ''If you think about this, I showed up in '85, when it was relatively 'safe.' We thought we had it figured out. I raced all the way through 2001 when people were getting killed. And all through that time, I was hitting my head and knocking myself out and getting concussions and going to the hospital. And I don't know what that means to me in 10 years. But I know it's a concern.''
The 48-year-old Waltrip gets uneasy when he hears stories about NFL players and other athletes who are having serious neurological problems after they retire, issues that a growing amount of research indicates may have been caused by repetitive brain injuries they sustained during their playing days.
Could that happen to him, too?
''I would be the perfect case study to see what's going to happen,'' Waltrip said. ''Because I can go back and look at the races and count up times I was knocked unconscious that I can't count on both hands.''
Five-time NASCAR champion Jimmie Johnson says he has had two concussions racing stock cars, and probably many more racing dirt bikes when he was younger.
''We're not immune to concussions,'' Johnson said. ''And certainly after severe concussions or being concussed several times, the numbers change. We know that. The dynamic is there. I think we've reduced the opportunity for it to happen, but ultimately, it can happen. I just think the odds are a lot better today than they've ever been.''
Earnhardt's death in the 2001 Daytona 500 - which came after drivers Kenny Irwin, Adam Petty and Tony Roper all were killed from similar head injuries - forced NASCAR to get serious about safety.
Today, drivers must wear a head and neck restraint, while impact-absorbing SAFER barriers have been installed on racetrack walls and NASCAR completely redesigned race cars to reduce the risk of injury. Racing seats used to look a lot like passenger car seats; now they look more like something out of a spaceship, with foam-padded supports on each side of the helmet that barely allows a driver's head to move during a crash.
It's working. Going into Sunday's Daytona 500, there hasn't been a death in NASCAR's top three national series since Earnhardt's.
''If I'm Kasey Kahne or Kyle Busch, I don't have those concerns any more,'' Waltrip said. ''We've got the cars and the tracks, we've got it all fixed. You can still get hurt. You're running 200 miles an hour. But the chances of getting hurt are slimmer. The chances of hitting your head and hurting it are really slim.''
NASCAR officials say they've identified 29 concussions in their top three series since 2004 - and only 11 of those happened in the past five seasons.
''Not huge numbers, when you see it,'' said Steve O'Donnell, NASCAR's senior vice president of racing operations. ''But with each of those, each one's different, we've had to assess each one differently. Knock on wood, we haven't had as many to have to deal with.''
And while there have been some drivers who experienced long-term effects from traumatic head injuries over the years - including Bobby Allison, Ernie Irvan, Jerry Nadeau and Steve Park - O'Donnell says NASCAR doesn't see any evidence of widespread health issues related to multiple head injuries, as the NFL and other sports are.
''There's always concerns for any driver that's been in the sport,'' O'Donnell said. ''But in terms of drivers formally approaching us and saying, `Hey, I want to talk about this or look at it,' we haven't seen that occur, in terms of what you're seeing in other sports right now. We'd certainly be open to working with anyone, if we see that, in helping to stop any trend that we saw.''
In response to reports of football players, hockey players and other athletes having serious neurological issues in retirement, researchers at the Boston-based Sports Legacy Institute have studied brain tissue of deceased former athletes. They've found evidence of a degenerative brain disease known as Chronic Traumatic Encephalopathy that has been linked to repetitive brain injuries.
O'Donnell said NASCAR officials have noticed.
''Absolutely,'' O'Donnell said. ''It's something we pay attention to on any aspect of other sports, what they're doing. Can we learn from it? Can we implement some of these things? We're open to working with any other sport as well.''
For now, veteran driver Jeff Burton is trying to gather as much information as he can about the long-term effects of concussions. Burton's father-in-law is a physician and has attended sports medicine conferences on his behalf.
''I think anybody that has any sense at all has to understand that it doesn't matter if you're playing football or hockey or racing a car, head injuries can have bad ramifications later in life,'' Burton said. ''It appears to be the case. I think we are exposed to less of it. But at the same time, when we do have them, they can be big hits.''
The 44-year-old Burton started racing in NASCAR's top division in 1993, well before the post-Earnhardt safety advances.
''I can tell you that in retrospect, there's been many times that I've had concussions,'' Burton said. ''And the definition of concussion is a very widely used term, and how you actually define a concussion has changed over the years. But there's no question that with hitting concrete, not having (today's safety equipment), there's no question people had concussions. No question.''
Waltrip said he blacked out after an accident in practice at Las Vegas in 1998, but kept it to himself.
''Hit the wall, got in the backup car, made a couple laps, went to the hotel, woke up the next morning, didn't even know how I got there,'' Waltrip said. ''You could just fake people out back then. `Yeah, I'm fine, I'm fine.' They didn't care. 'OK, you're fine.'''
Today, any driver involved in a significant accident must visit the infield medical center, where checking for signs of a concussion is standard procedure. If there's reason to suspect a concussion, the driver will be sent to a local hospital. From there, the driver will need to be cleared by a neurosurgeon with at least five years' experience in sports-related head injuries before he or she can race again.
''They always ask you,'' Burton said. ''The key to that, though, is honesty. Unless it's obvious. Sometimes you can tell. But a lot of times, in football and in every sport, people say, 'I'm fine.' It's hard if you don't tell them the truth to help you.''
Burton acknowledged that drivers, along with athletes in other sports, have an incentive to hide symptoms.
''There's fear in not being able to do what you want to do,'' Burton said. ''NASCAR's always been really good saying, 'Look, we don't want to keep you from racing unless it's in your best interests.' They've been pretty good about that. People are always nervous, I think, in any sport to stand up and say I'm having these issues, because they want to race or they want to play. But if NASCAR doesn't want you to race, then you probably shouldn't be racing.''