Until he landed in the emergency room last June, Joe Johnson had run every day for 21 years. A mystery virus interrupted that streak, but he refused to allow it to end another one.

Johnson left the hospital, drove to Duluth from his home in Menominee, Mich., and ran in his 36th consecutive Grandma's Marathon. He was promptly readmitted to the hospital for four days, but he had retained his membership in the three-man club that has made the run from Two Harbors to Canal Park every year.

"My rules are, nobody is allowed to get married or die on this weekend," Johnson said. "I was sicker than heck, but I wasn't going to miss Grandma's."

Johnson, Jim Nowak and John Naslund raced those 26.2 miles for the first time in 1977, when Canal Park was largely an industrial area that attracted more rats than people. None could picture what they will see Saturday. More than 15,000 runners from 40 countries and all 50 states will flood Duluth for Grandma's Marathon and the Garry Bjorklund Half Marathon, with 6,000 volunteers and thick crowds of spectators lining what was once a quiet, lonely course.

Last Friday, Johnson, 63, went to the emergency room again after tripping on a log during a training run. Though he was idled for a few days — and is dealing with a nerve injury to his foot — he plans to hobble his way through. Naslund, 63, is well-prepared after running the Minneapolis Marathon on June 2, marking his 40th consecutive year of running at least two marathons.

Nowak, 62, swore he would never go the distance again after getting sick in the heat at the first Grandma's. Years later, when his pregnant wife's due date fell on race day, he was plotting ways to avoid missing one blessed event for another one.

"My son was born early, but I had planned in my head that I would drive up at midnight, then jump in the car and drive back right afterward," said Nowak, a Duluth native who now lives in Reedsburg, Wis. "It just became a lifelong thing. You put that day away, and nothing's going to interfere with it."

In 36 previous editions of Grandma's Marathon, there have been 175,626 finishers, with Nowak, Naslund and Johnson the only ones to race every year. Dubbed "The Iron Three," the trio were inducted into the Grandma's Marathon Hall of Fame in 2002, a year after they and the race hit the 25-year mark.

Nowak, a retired teacher, and Naslund, a stockbroker who lives in Bloomington, were college track teammates at Minnesota Duluth in the early 1970s. They were members of the North Shore Striders track club, where they came to know the men who founded the race along their scenic training route.

Naslund, a native of Two Harbors, was a pole vaulter at UMD who took up running in 1972 to get in shape; he tackled the first Grandma's after running the Boston Marathon in 1974. Nowak had tried one marathon and wanted no part of another, but friends persuaded him to enter the hometown race his club was launching. Johnson, who began running in 1970, drove over from Michigan with some pals who thought it sounded like fun.

They were among 150 people who paid $3 each to run. Naslund finished fifth — the best finish of any of the Iron Three — in the inaugural Grandma's, which all of them remembered for its 11 a.m. start on a hot day.

All three men said their families willingly honor the marathon's sacred status on their summer calendars. Some of Johnson and Naslund's favorite editions of the race are the ones they have run with their children, with Naslund's wife also joining him for several years.

"Now she's wondering how long I'm going to keep this going," said Naslund, who has run more than 150 marathons, including several in Boston and New York. "At this point, you think, 'What would stop me?' If someone has a funeral in the morning, I'm not going to get there."

By the 10th year of the marathon, the men said, race organizers were recognizing the diehards. At that point, Naslund recalled, there were between 10 and 15 people who had run them all. The number gradually dwindled as other streaks were ended by injuries or family obligations.

Nowak remembered that back then, he hoped he could make it through the first 20 Grandma's Marathons. His new target is 50. He will be 75 when that race is held in 2026, but he remains a man obsessed. His scariest dreams are of going to the wrong city for the start of the race, and he uses three alarm clocks to make sure he awakens on time.

"One year I stayed overnight with my dad at his assisted-living facility and got locked in the night before the race," he said. "They didn't unlock the doors until 7 in the morning. I found a back way out, but I was ready to break a window."

The trio have suggested that the race create a new award: a belt buckle for those who reach 1,000 Grandma's Marathon miles. Not that they need any extra incentive to keep returning. Naslund said he plans to continue running Grandma's as long as he is able, while Johnson — who has his eye on the 40-year mark — already has proved the lengths to which he is willing to go to get to the start line.

"If I have to walk part of it, I will," he said. "We always have such an awesome time. I feel more at home there than anywhere."