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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