In this April 19, 2015 file photo, NASCAR driver Jimmie Johnson runs through the tunnel during a rain delay in a Sprint Cup Series auto race at Bristol Motor Speedway in Bristol, Tenn. Johnson plans to run in the Boston Marathon on Monday, April 15, 2019. AP file photo

BOSTON — Just because he won’t be surrounded by 3,300-pound cars traveling at more than 200 mph doesn’t mean Jimmie Johnson will be able to relax when he runs the Boston Marathon on Monday.

If the seven-time NASCAR champion isn’t thinking about his heart rate or his pace, he’ll be concentrating on the conditions or the course or whether he is drinking enough water.

In that way, it’s a lot like his regular job.

“If it’s a lap time I’m trying to hit or a heart rate you’re trying to hit, either way it’s not comfortable,” Johnson said during a break from the two-way training he has undertaken to get ready for a 26.2-mile footrace in the middle of the NASCAR season. “You’re in very similar head space. It’s shocking how similar it is.”

An 83-time winner on the racetrack — sixth most in Cup history — Johnson has long been a fitness freak who swam in high school and has always run and cycled to stay in shape for driving. Now 43, he has a bit of a bucket list of athletics events he wants to complete; he has already knocked off a couple of mini triathlons and half marathons as well as the Assault on Mount Mitchell, a 102.7-mile with a 10,000-foot vertical climb up a North Carolina mountain that he rode with Jamie McMurray and Matt Kenseth.

“Training is a part of every race car driver’s life,” said Johnson, who will wear bib No. 4848 as a nod to his No. 48 Chevrolet. “Certainly, getting ready for a marathon is more than the normal event. There’s just a lot of miles required.”

That was the biggest surprise, Johnson said, when he shifted his training from fitness to getting ready for a three-hour race. He has run up to 80 miles per week to get ready, though it tapered down to about 20 as he got closer to race day.

“It’s not like I’ve not run before, but to increase the volume and the daily miles required. It’s crazy what you put your body through,” he said. “I’m enjoying this taper right now. But honestly, I’ve loved the experience and enjoyed all the pain and suffering that comes with it.”

Fitting the training in with his driving has been a challenge that at times has required him to get up at 5 a.m. to run. He’s used his travel schedule to his advantage, finding running paths near the track that provide the hilly terrain he needs to prepare for Boston’s challenging course.

His competitors have noticed.

“Jimmie Johnson is crazy,” Daytona 500 winner Austin Dillon said. “He’s a seven-time champion and he still tries to come out here every weekend and kick everybody’s butt. He’s a different animal and I respect him for that.

“He can probably do whatever he wants. I think he’s a freak. He’s a beast,” Dillon said. “You see him out here, out running, sweating and I’m trying to stay as hydrated as I possibly can, and he’s got a different process. And it obviously works for him.”

Johnson might not have even been able to run Boston but for a quirk of the schedule that had NASCAR racing Saturday night in Richmond, Virginia; he finished 12th after failing prerace inspection and getting sent to the back of the grid. The marathon is held on the traditional Monday Patriots’ Day holiday, giving him about 36 hours to recover from his drive, which typically leaves him with a sore lower back, glutes and hamstring.

That’s earned him no slack from his coach, Jamey Yon.

“In his world, he thinks that Sundays are an off day for me,” said Johnson, who can sweat off five to ten pounds per race. “In my opinion, the car is part of my workout and I’m putting in seven days a lot lately. There’s a huge physical component to it.”

Johnson ran the Daytona Half Marathon in 1 hour, 33 minutes, and is hoping to break 3 hours on Monday.

“I know that’s a very lofty goal,” he said.

McMurray ran a marathon in December in 3:14:06 — good enough to meet the Boston qualifying time — but the race filled up with faster runners. Johnson, who got his Boston bib through a sponsor’s exemption, tried to draft him as a running buddy, but McMurray wants to qualify on his own.

“If I could run fast enough to make it in on my time, then I would probably go do that,” he said. “Only because in the running world people spend their whole life trying to qualify for Boston.”

Johnson has gotten some pushback on social media from fans who think his side gig is hurting him on the racetrack; he hasn’t won in almost two years, and this year he is adjusting to a new crew chief and new sponsor for the first time in his career.

But Chase Elliott, Johnson’s 23-year-old teammate at Hendrick Motorsports, thinks the running actually helps.

“You live in this world, and you are traveling so much and it is just racing, racing, racing,” Elliott said. “I think that is his way of disconnecting and doing his own thing to clear his head. It is something he enjoys and just so happens to be good for him. Kudos to him.”

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AP Auto Racing Writer Jenna Fryer contributed to this report.