There was a surge in Boston Marathon participation this year on Nantucket, with 13 island runners slated to be at the starting line in Hopkinton Monday, but the biggest story is the man who won’t be running.

After 48 straight years of running in and finishing the Boston Marathon, Dr. Tim Lepore is hanging up his sneakers, at least for this year.

“My back hurts just walking around. It’s painful. It isn’t that I don’t want to run. I want to run, I just can’t,” Lepore said. “If this improves I’ll get more in and aim for 50 (Boston Marathons finished).”

And so the second-longest, consecutive-finish streak in the history of the Boston Marathon comes to an end. Lepore was just one marathon finish behind record-holder Ben Beach, who began his streak in 1967, a year before Lepore. Beach, a 67-year-old runner from Bethesda, Md., is slated to run the marathon again this year.

Lepore first ran the marathon on a bet with a buddy, who didn’t think Lepore could make it to the Happy Swallow Pub, in Framingham, only 6.5 miles into the 26.2-mile marathon course. Not only did Lepore win the bet, he did it easily.

“I felt pretty good when I got to the Happy Swallow, so I decided to keep going. But then (near the finish) I didn’t feel so good,” he said.

Having only prepared for a run of less than a third of the full marathon distance, his legs began throbbing and the skin on his feet started peeling, but Lepore finished. And the experience woke something inside him.

“I used to run in college and medical school for exercise but then (after the first Boston Marathon) it got out of hand,” he said.

Over the next 40 years, Lepore became immersed in long-distance running, going on to run marathons on back to back days and participating in ultra-long-distance marathons of 50 or more miles. His personal record is running 87 miles in a 24-hour period.

“It’s beautiful. You’re just motoring along, and you never know what kind of a day it will be. I love it, running early in the morning or late in the evening, running on the trails, the dirt roads, it’s so quiet, it’s the most relaxing thing I do,” Lepore said.

Over his 48 years running Boston, Lepore has seen it all. When he first started, only men raced. It wasn’t until 1972 that women were allowed to compete.

There was the time in 1975, when Lepore said he ran “more like a god than a man,” finishing with a time of 3 hours, 12 minutes and eight seconds. “I was flying and I felt great,” he said.

On the other end of the spectrum there was 2008, when Lepore had to gut out the race only 9 days after an operation on his knees.

Lepore also had the opportunity in 2014 to run with his friend Robin Harvey, who died in 2015 after being hit by a car while training for her second Boston Marathon.

“When Robin ran, she passed me around Wellesley and I liked to tell people she slapped me on the ass and yelled, 'See ya, fat boy.’ But she didn’t, she was very gracious as she ran by me,” Lepore said.

This year, six friends and family members of Robin Harvey are running in the marathon on behalf of the Spaulding Rehabilitation Hospital: Harvey’s daughters Adriene Lombardi and Keri Harvey as well as friends Liza McKenney, Michael Dussault, Liz Reinemo and Jena Winchell.

Robin Harvey spent time recovering at Spaulding in Boston after being struck by a car on her bicycle in 2012. Finishing her first Boston Marathon in 2014 was a high point in her recovery from that accident. She ran the race with her daughters for the Spaulding Foundation.

Nantucket resident Kelsey Perkins will also be running in Monday's marathon. Perkins, a nurse practitioner in Lepore’s office, will be running for the 26.2 Foundation, wearing the bib Lepore would have worn if not for his injury.

“When Dr. Lepore wasn’t physically able to train, I said I would do it, so we kind of flip-flopped,” Perkins said. “I had a moment where I said this is somebody who has done so much for me both personally and professionally and I just felt like I should do it for him.”

But Perkins isn’t expecting to follow in Lepore’s footsteps. This, she said, would most likely be her first and only Boston Marathon.

“I felt like this was something to do to honor him because running 48 (Boston) marathons is a huge accomplishment,” Perkins said.