They both went into business 30 years ago, with what was then a new and unproven concept: a store devoted to selling running shoes. Now, as they prepare to retire, two prominent local retailers are turning to a traditional method of small business succession:

They’re turning it over to their kids.

The Gubbins running specialty stores on the East End and the Runner’s Edge in Farmingdale — founded by families related through marriage — are in the midst of transitions to a new generation.

“When my mom opened the store in 1987, I was in a crib in the store,” jokes Geary Gubbins, 29, who now owns one of the family’s four stores. “All I know is the business.”

A slight exaggeration: Although he did grow up around the flagship store, Gubbins Running Ahead in East Hampton, Geary attended Duke University on a track scholarship and was thinking about a career in law. Instead, after graduating from college, he began to take an expanded role in the family business — and in 2014 opened his own store, Geary Gubbins Sports in Southampton. Plans are that when his mom and dad, Barbara and Justin, retire, he will take over the other three family stores in the Hamptons.

Justin’s cousin Sue is married to Bob Cook, who opened The Runner’s Edge in 1985. Their daughter Allison, now 30, was turned away by her dad when she first asked about employment at the store. “He wouldn’t let me work here when I was in high school,” says Allison, laughing. Instead, she worked in a local supermarket while she was a teenager. (“I wanted her to see what it was like to work for someone else, instead of getting a free ride,” said Bob Cook.)

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Allison, who majored in education at Eastern Connecticut State University, decided that a teaching career was not for her. Like Geary Gubbins, she instead found herself taking a larger role in the family business. “I loved the staff here, I loved the store,” she says. “And I’m really interested in fashion. I gravitated towards that.”

Now, eight years since joining the staff after graduation from college, she is poised to take over the business — although no firm date for her father’s retirement has been set.

What’s happening with the Gubbins and Cook families is not typical among the nation’s estimated 1,000 running specialty stores, many of which were founded during the running boom of the 1970s and 1980s. “A lot of owners are left wondering how they’re going to exit the business,” says Terry Schalow, executive director of the San Diego-based Running Industry Association. “The common strategy is to sell to larger groups.”

Cook says he had such an opportunity. “But because Allie was here, I said ‘no thanks,’ ” he says.

Barbara Gubbins, a registered nurse who loved to run, says long-term planning was not part of her vision back in the 1980s. “It was never like ‘I’m going to be a successful business person,’ ” she says. It was like ‘this would be cool!’ ”

Both Geary Gubbins and Allison Cook bring new ideas to their respective businesses, at a time when internet competition is pressuring brick-and-mortar retailers of all kinds.

“These are challenging times,” Barbara Gubbins says. “You have online vendors competing against us. You can buy running shoes on Amazon!”

Still, overall sales are growing. Wholesale sales of running shoes totaled $4.4 billion last year, up from $3.6 billion in 2010, the Sports and Fitness Industry Association says.

For her part, Allison “is building stronger community ties with a younger generation,” says Geary. “We’re doing the same thing, but in a different situation.”

The younger Gubbins has expanded the store’s apparel lines, aiming at local consumers. “I take a brand such as Under Armour, and I print local sports team’s logos on shirts,” says Geary. “So if a kid comes in and he’s looking for his new pair of cleats or running shoes, hopefully he’ll see team apparel, a nice Southampton High School soccer or track-and-field T-shirt.”

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Allison Cook is aiming at younger runners, beefing up the store’s social media profile — the Runner’s Edge now has about 3,600 Facebook followers — and creating offbeat, millennial-friendly events, such as a scavenger-hunt run last summer to help promote the new Brooks Ghost running shoe. About 25 participants ran around Farmingdale’s Main Street, searching for strategically placed images of famous ghosts and capturing them on their cellphone cameras.

While both Geary Gubbins and Allison Cook recognize that they will be taking over at a time when participation in running has declined slightly after years of growth, neither is worried about the future. “Running is one activity that I don’t think will ever die,” Allison says. “People are always going to want to stay fit.”

The sport certainly looks healthy this week: With the New York City Marathon coming up, the Runners Edge will be hopping, particularly on Sunday when about 160 local participants will meet there early to take three chartered buses to the start line in Staten Island.

As for the long-term health of two of Long Island’s best-known running specialty stores, it’s soon going to be in the hands of the next generation.

“My parents are getting tired,” says Geary Gubbins. “When you’ve been doing it for thirty years, retail can be mentally and physically exhausting. A new face and new energy can really bring a lot of life to a business.”