Ben Beach, running along the Capital Crescent Trail near his Bethesda home, has completed 43 consecutive Boston Marathons, the second-longest streak in history behind only Neil Weygand, who has a current streak of 44 in a row. (Doug Kapustin/For The Washington Post)

Bethesda’s Ben Beach has run 43 straight Boston Marathons, but gone are the days when he could be seen near the elite women’s leaders of the legendary road race. A distance he once covered in less than 21 / 2 hours now takes nearly five.

Beach is 61 years old now, and he suffers from a neurological movement disorder known as dystonia. His left leg swings awkwardly with every stride. He runs sparingly, perhaps 10 miles per week.

Yet he will be at the starting line Monday morning, as he has been every Patriots’ Day since 1968, expecting to traverse the full 26.2 miles of the 115th Boston Marathon, past Wellesley’s shrieking collegians, up Heartbreak Hill and into the throngs at the finish, for the 44th consecutive time.

Now, Beach runs — even though he can barely run — because he cannot stomach the idea of the race going on without him. He finished in 4 hours 40 minutes 35 seconds last year.

“A lot of people wonder how crazy I must be to keep doing this, especially if they’ve seen me running. It’s not a pretty sight,” he said. “I’m just so caught up in the streak . . . I can’t seem to find a way to stop.”

To Carol Beach, Ben’s wife, this is normal. She does not worry about her husband, whom she met at a road race in Rock Creek Park. She does not fear for his health. She does not consider that he will not finish.

“The only way it would be,” she said, “is if he fell down unconscious during the race. He’s told me he would crawl if he had to. What am I going to do?”

She will just have to cheer. Years ago, she realized her husband’s annual jaunt through Boston’s heart was as much a mission as a marathon. Beach has run five labored Boston Marathons on a bum leg and 38 with two strong legs at impressive speeds. He has competed on pleasant days and in near-monsoons, in fields with Bill Rodgers, Joan Benoit, Rosie Ruiz and Uta Pippig.

Beach hopes to outlast his spirited rival in Boston streakdom: Neil Weygandt, age 64. Weygandt has run 44 straight Boston Marathons, which gives him a one-year edge on Beach for the all-time record. The two exchange holiday cards and greetings on race day, but there is no question each wants to outkick the other in the race for record longevity, and neither expects the other to quit.

“I just assume Neil is going to show up,” Beach said. “The two of us will stagger toward the finish, and chances are both of us will get there — though it takes longer and longer and longer.”

Beach ran his first Boston out of curiosity as a freshman at Harvard, finishing in 3:23.50. He ran for fun and competition for years after that, posting a personal best of 2:27.26 in 1981 — just 40 seconds behind the women’s winner.

He considered dropping out only once, when his knee got sore during his fourth race in 1972. He couldn’t find a ride to the finish, so he just kept running.

Beach earned a law degree at Catholic University, assisted with George McGovern’s presidential campaign, worked for a former Michigan lawmaker on Capitol Hill, met and married his wife, fathered three children, put them through college, wrote for various magazines and became senior editor at the Washington-based Wilderness Society as he knocked off one Boston Marathon after another.

Yet he displays virtually no memorabilia from his Boston races. His race numbers sit in a box. Only a single trophy from a victory at a marathon in Fairbanks, Alaska, occupies a public perch in the basement. Beach doesn’t care to be nostalgic, at least not yet.

He’d prefer to look to the next race, or ponder the achievements of those who inspire him to keep going. Which is perhaps the reason his basement does feature a framed photo of Olympic marathoner Johnny Kelley, who ran a record 61 Boston Marathons, finishing 58, before he stopped in 1992 at age 84.

“If I am lucky enough to get to 62 [Boston Marathons], I would be 80 years old,” Beach said. “I think I kind of figure that would be the point at which I might say, ‘Enough.’ ”

Or maybe not.

“People who know me, and know how dug in I am, would say, ‘No, Ben is not that sensible,’ ” Beach said. “ ‘He will run until they come in with a stretcher and carry him off.’ ”

Beach takes pains to keep himself out of the path of stretchers. Though he can’t log the 60 miles a week he once handled, he still works out twice every day. A typical week, he said, includes three runs, five or six bike rides, two weight-training sessions, three elliptical trainer workouts and one or two rides on an exercise bicycle. From May to September, he tosses in three swims.

In 2002, Beach began to notice an odd sensation in his left leg. There was no pain, just an inability to use the leg as usual. It took four years before a neurologist at the George Washington University Hospital diagnosed the disorder, which in Beach’s case shows up as a failure of his brain to process instructions from his left hamstring.

As Beach adapted to a new, uncomfortable stride, he began sustaining injuries to other parts of his body. He realized he had to modify his training to ensure he could keep racing.

“Running is not as fun as it used to be, because it’s awkward,” he said. “It’s an effort. But it’s still better than not running. It’s something that’s important to me.” His time in the marathon would no longer qualify him for Boston, but after he completed his 25th straight, organizers gave him a lifetime pass into the field.

Beach, who also has run 39 consecutive Cherry Blossom Ten Mile Runs, is focused on finishing the Boston Marathon in less than six hours, when the race officially “closes,” to ensure that his result actually counts.

“I care, but I can’t get too caught up in it,” he said. “It’s kind of discouraging to see how much slower I am. My main goal is to finish. My second is to do it as quickly as I can.”

Knowing how their father was struggling, physically and mentally, with his dystonia, his children Carter (30), Emily (28) and Evan (24) teamed up to run legs with him at the 2007 race. Attempting to describe that year’s event leaves Beach repeatedly choked up.

That year, he had been worried about the possibility of terrible weather. He was still struggling to adapt to his distorted gait. He feared his streak would end at 39. And his children surprised him on race weekend, announcing they would join him along the course to push him along. It’s the only time they’ve ever run with him. And it worked.

“I really wanted it,” Beach said. “With the dystonia being such an obstacle, and having the kids . . . It was very sweet.”

Emily won a national championship in 2005 with the University of Maryland field hockey team and was recently named head coach of the women’s team at Stevens Institute of Technology in Hoboken, N.J. Even so, she can’t bring herself to compare her achievements to her father’s.

“I feel like he’s accomplished way more than I ever could athletically,” Emily said. “When I tell people what he’s done, they’re blown away.

“When he got to numbers like 35 and 40, it’s crossing into unbelievable. . . . We not only assume, but just know, that he’ll finish. It’s not up for debate . . . He’ll get there.”