Dale Earnhardt Jr. has started slowly in the NASCAR Monster Energy Cup season. He goes into Sunday's event at Martinsville Speedway without a top-10 finish in five races, his longest drought in a season since 2011.

He is enjoying every minute of racing in the middle of the pack.

"It's been a lot of fun inside the car," said Earnhardt, who will compete in the O'Reilly Auto Parts 500 at Texas Motor Speedway next Sunday. "I've had a good time every race. We just haven't had good finishes."

The finishes will improve if Hendrick Motorsports finds the speed that Earnhardt's No. 88 Chevrolet has been lacking from the beginning.

There is no problem with the driver, which is significant.

Earnhardt missed the final 18 Cup races last year because of debilitating concussions. Earnhardt said he has made it all the way back from that hellish experience to be at the top of his game.

"I don't think I'd be in the car if I wasn't," Earnhardt said. "You can't get out there with any kind of limitation. I definitely wouldn't want to be in the car if I didn't feel I was 100 percent. If you're not 100 percent, you don't need to be in the car."

Earnhardt's willingness to be transparent about the condition and get the help of a neurologist had a long-ranging effect on NASCAR's approach to the issue of concussions. When NASCAR's most popular driver speaks, people listen.

Earnhardt's father, the seven-time Cup champion, likely had numerous concussions. Drivers in that era hid their conditions to stay on the track.

The son did something similar in 2012, and that led to his involvement in a wreck at Talladega Superspeedway. Earnhardt almost made the same mistake again.

He incurred the concussion in a crash, his fourth of the season, at Michigan International Speedway in June. He ran in three more races before acknowledging persistent balance and vision problems. Earnhardt got out of the car and went to Dr. Jerry Petty, a neurologist in Charlotte.

"I was incapacitated," Earnhardt said. "I couldn't do my job, much less typical everyday things. I was desperate to get it figured out.

"Every concussion is different. It's like walking through a haunted house. You don't know what's going to jump out at you. ... That scares you, because you're feeling something new and different with each one you have. That gets you right in front of the doctor quick."

There were moments while under Petty's treatment that Earnhardt thought he would never get back on the track. His balance and vision slowly returned to normal.

Earnhardt returned to the track in December at Darlington Raceway for a special test session and received medical clearance from NASCAR to rejoin the Cup series.

In February, NASCAR also unveiled a new concussion protocol in which any driver involved in an accident that sends him behind the pit wall must be evaluated for head injuries. NASCAR also increased its neurological support at race weekends.

That's a long ways from the thinking that was prevalent early in Earnhardt's career. Of all the things Earnhardt has accomplished in what TMS president Eddie Gossage said is a Hall of Fame career, his role in the advancement on concussions is the most significant.

"It's hard to me to take any credit for doing the right thing, because I was scared into that situation," Earnhardt said. "The idea was most concussions would just go away. You didn't hear the horror stories you hear today.

"And you definitely didn't hear about the long-term effects. We were so uneducated about it."

Everyone in NASCAR is more knowledgeable about concussions because of Dale Earnhardt Jr.'s nightmare.

Junior's best tracks

A look at the tracks where Dale Earnhardt Jr. has had the most success in the NASCAR Monster Energy Cup series: