Michael Westphal was close enough to see the marathon finish line clearly, so he decided to put on a show. Over the final 50 yards he would shift into high gear past the cheering fans and flapping flags on Great Cranberry Island, off the coast near Mt. Desert Island.

“I started leaning forward,” he said, “but my legs just didn’t follow.”

He pitched forward, extended his hands to brace himself but failed to prevent the left side of his face from smacking asphalt.

“It was kind of like slow motion,” he said. “I could feel it but I couldn’t stop it.”

This sort of thing can happen when you have Parkinson’s disease.

Undaunted, he pushed himself up to his knees, took two quick steps … and fell again.

At that point a thought ran through his mind.

You fool. You just had to sprint to the finish, didn’t you?

This time he rolled to his side and spread his feet wider to create a sturdier base. He walked his hands toward his toes, pushed off with his fingers and stood upright, pausing briefly to walk seven steps before resuming his splay-footed stride amid cheers and whoops.

Michael Westphal of Great Cranberry Island refuels after completing The Great Run marathon in June.

“Absolutely amazing, Mike,” shouted a tinny, megaphone-enhanced voice as Westphal pushed through a finish-line banner held by two girls in yellow T-shirts. “The whole island is cheering for you today!”

Westphal, a 58-year-old carpenter, will run before a much larger audience Monday when he attempts to complete the Boston Marathon for the first time in 30 years. He earned his qualifying time by completing The Great Run marathon last June in 3 hours, 32 minutes, 56 seconds. For Boston he only needed to break 3:40.

“He was a good runner and he gave it up for years,” said Rolf Westphal, 51, who lives in Cumberland and will run alongside his older brother over the 26.2-mile route from Hopkinton to Copley Square. “But after he was diagnosed (in 2006), he decided ‘I’m not going to sit around and let this thing take over.’ He’s going to go out and live life. He’s out there doing what he likes to do no matter what comes his way.”

Of the six Westphal children, five wound up running distance for Mt. Desert Island High. Joan Westphal, a 1977 graduate, holds the distinction of beating future Olympic marathon gold medalist Joan Benoit Samuelson in a state championship mile.

The family moved from Minnesota to Cranberry Isles in 1970 when Mike, the third oldest, was 13. After high school he continued running at the University of Maine, through his graduation in 1979, and on to local road races, with his best years in the early ’80s.

He won the Paul Bunyan Marathon in 1980 (in 2:29:32) and the Bangor Labor Day race in 1982.

After getting married and starting a family, Westphal dropped off the road racing circuit and ran only for fitness. He looked after his carpentry and caretaking business, which oversees about 35 summer properties on the islands just outside the mouth of Somes Sound, near Southwest Harbor below Mt. Desert Island. He coached Little League baseball. He raised two sons.

The first symptoms of Parkinson’s started appearing in 2003 but it took three years before Westphal received a formal diagnosis. His older sister, Gretchen, also has the disease, as did several aunts and uncles.

As it turned out, running helped alleviate Westphal’s symptoms. Medication also provides some relief, replacing the dopamine no longer produced by brain cells, as is the case in healthy patients.

Parkinson’s is a chronic and progressive movement disorder affecting a half-million Americans. There is no known cure, but the National Institute of Neurological Disorders and Stroke (NINDS) supported $146 million in research in fiscal year 2015.

Danny Paul, the Falmouth High track and cross country coach who grew up in Portland and ran competitively at Northeastern, is a few years older than Westphal. They both ran Boston in 1985 and crossed paths several other times.

“Before the Parkinson’s took over, he was just a good runner,” Paul said. “Not a top-top guy but in that next group, in the 2:30, 2:40 (marathon) range.”

Paul, now 62, lost track of Westphal until beginning a running camp on Mt. Desert Island seven years ago.

“That’s when I got wind that he was training, but that he had the Parkinson’s and they didn’t know what he could do,” Paul said. “I kept getting more feedback that in spite of it he was running these amazing distance runs.”

Five years ago Paul took a group of campers for a fun run on Great Cranberry Island.

“I saw Mike then and even walking looked hard,” Paul said. “And yet he was running 10 miles a day. It’s almost like what they tell older people: If you stay active, you don’t lose it.”

Michael J. Fox, the actor who gained fame on television’s “Family Ties” and cinema’s “Back to the Future” trilogy, disclosed his Parkinson’s diagnosis in 1998, seven years after receiving it. His research foundation claims to be the world’s largest nonprofit funder of Parkinson’s drug development, and inspired Westphal’s marathon return.

With a modest goal of a few thousand dollars, Westphal was surprised when more than $38,000 in donations came in. Footage of his unintentional tumbles was posted on YouTube and has been viewed more than 5,400 times. A moving 12-minute documentary called “Outrunning Parkinson’s” produced by Peter Logue of Southwest Harbor is approaching 10,000 views on Vimeo.

Rolf, who paced Michael for the last 16 miles of the Great Run, ran the entire MDI Marathon with him in October. Their time was slower, but Michael found he had run with a broken pelvis.

“I thought it was a pulled muscle,” he said. “I remember jumping off the deck stiff-legged and feeling a little bit of a pull. I took 12 days off (from training) because of the injury. I don’t know if it broke during the race or earlier. It just got painful about two miles out.”

Michael Westphal picked himself up – as he has done since learning he has Parkinson’s disease in 2006 – and keeps living his life as he wants. That includes finishing the race on Great Cranberry Island.

Westphal was on crutches through November before being able to walk and ride a bike. In late December he started running again but wasn’t free of pain until February.

As one of the Fox Foundation’s top fund-raisers, Westphal was a guest speaker at an awards dinner in New York City on Friday night. He created another fundraising page for Monday’s Boston Marathon. He and Rolf – who qualified with a 3:15 in New York City last fall – are scheduled to run in the second wave beginning at 10:25 a.m.

“We’re going to try to go out at an 8-minute pace for the first 10 miles, shooting for a 3:30 finish,” Rolf said. “But to finish is the ultimate goal.”

Michael’s last attempt at Boston ended with a knotted calf muscle in Mile 9. That was in 1993.

“I just want to inspire people to step outside themselves and attempt something that they never thought was possible,” Michael said. “That’s my hope.”

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