If the particulars of Alex Salazar’s transformation from couch potato to marathon man are fuzzy — he calls his efforts “pretty casual” — the benefits are clearly defined. In addition to toned pectorals and fierce quadriceps, Mr. Salazar gained a sense of purpose and a bustling social life after he started running and working out in 2012.

He also lost 50 pounds and met Krissa Cetner, who would vow to help keep him heart healthy, in both the physical and emotional senses. Though the courtship of the two fitness devotees hardly took place at a frenetic pace, it culminated in the middle of the Brooklyn half marathon on May 20.

Mr. Salazar, now 39 and a technology consultant, first met Ms. Cetner, 36 and a nurse practitioner at the Hospital for Special Surgery in New York, at a volleyball game in Manhattan in the fall of 2012. Mr. Salazar had signed up to referee, and Ms. Cetner had been playing on the Casual Sets team for years.

“So it’s my first time reffing by myself, and I’m all nervous,” Mr. Salazar recalled. “I’m fumbling around with the net, and it’s like 10 minutes in, and Krissa was the closest player to me. I said: ‘Hey, I’m new here and I don’t know what I’m doing. Can you help me?’”

She could. But there was no immediate tug of attraction; Mr. Salazar had a girlfriend, and Ms. Cetner was too interested in spiking the ball to take much notice of him.

“He seemed like a nice guy,” she said, “but I didn’t think much of it.”

That December, she broke her foot while going to block a shot, knocking her out of volleyball for a while. But by March 2013, she felt healthy enough to run in a chilly half marathon in Manhattan.

In the runners’ corral, she recalled, “I saw this guy who was all bundled up, and he looked familiar, but I couldn’t really see him that well.” Slowed by her still-healing foot, she lost him in the crowd.

During her first game back with the volleyball team, she recognized the bundled figure: “I said, ‘Hey, did you run the half marathon?’”

Mr. Salazar said he had, and invited her to join his running group, whose members capped their Tuesday night runs in Manhattan with tacos and beer. The invitation wasn’t meant to be flirtatious. Mr. Salazar was still in an exclusive relationship.

“But my personality has always been, like, the more the merrier,” said Mr. Salazar, who grew up in Brooklyn in what he called a festive Colombian family. His mother, Mavelly, and father, Dario, now live in Central Islip, N.Y.

Ms. Cetner soon began feeling relaxed around Mr. Salazar. “We could talk about anything,” she said.

One night after the runners had gathered, Mr. Salazar walked her to the subway. She was headed home, to her Upper West Side apartment and her cat, Bruce.

“We were standing there on the platform, and I had had a couple of beers, and I said, ‘You know, you and I would be amazing together,’” she said.

Mr. Salazar’s response was not the one most women, emboldened by a beer buzz and a runner’s high, dream of.

“I said something along the lines of, ‘I appreciate you being open and honest with me, but there’s not much I can do with that information,’” he recalled. “I put it out of my mind.”

Months later, Mr. Salazar was refereeing a volleyball game when Ms. Cetner noticed that something was wrong. “I had been in this relationship a year and a half,” he said, “and it was ending, really badly.”

Ms. Cetner asked if he wanted to go for beers.

“I wasn’t thinking, ‘Oh, great, here’s my chance’ or anything,” she said. “I was just thinking he might need to talk.” He poured his heart out. And then they went their separate ways, both dismissing Ms. Cetner’s drunken-crush admission in favor of a more substantial bond, rooted in friendship.

“We kept the idea of dating at arm’s length out of respect for each other,” Mr. Salazar said. Ms. Cetner, who had ended a long-term relationship a year before meeting Mr. Salazar, kept her attention on Bruce, and on her career. Mr. Salazar started seeing other women.

“But in the back of my mind, I knew there was something special about her,” he said.

It wasn’t just her long, athletic legs or the way she wraps her arms around anyone who merits a hug, he said. It was her character.

Ms. Cetner is as self-possessed as she is goal-oriented. She moved to Manhattan from Saratoga Springs, N.Y., in 2007 without much besides her nursing degree. She credits her parents, John R. Cetner of Ballston Spa, N.Y., and Deb Dittner of Saratoga Springs, who divorced when she was young, for her pioneering spirit. And for her excellent cardiovascular system.

“I did my first race when I was in my mom’s belly,” she said. “My parents were runners, and they would take me to races.”

By the summer of 2013, Mr. Salazar decided he was wasting his time dating other women. By late August, Ms. Cetner was spending most nights in Mr. Salazar’s Brooklyn apartment, and they had come up with nicknames for each other that have stuck: She is Baby Giraffe, a reference to her long limbs, and he is Beast, a nod to a workout video he follows.

Ms. Cetner finally moved in with Mr. Salazar in March 2015. Bruce went upstate to Mr. Cetner’s house, because Mr. Salazar is allergic to cats.

“Our relationship just flows,” Ms. Cetner said. Still, she had no idea that Mr. Salazar was planning to propose when they accepted an invitation to stay at a friend’s time share in Cancún, Mexico, in May 2015.

The right moment arrived at an archaeological site in Tulum.

“We were in ancient Mayan ruins, on a cliff overlooking the water,” Ms. Cetner said. “It had been such a great trip, and I said: ‘You’re my running partner, my darts partner and my life partner. It doesn’t get much better than this.’” Mr. Salazar knew an opportunity when he heard one.

“Speaking of life partner,” he said, producing a ring. Ms. Cetner’s acceptance was swift.

On May 20, Mr. Salazar and Ms. Cetner were married during the Brooklyn Half. By 7:30 a.m., Mr. Salazar was suited up in a running shirt silk-screened with a tuxedo motif. Ms. Cetner pulled on spandex pants and a white sleeveless top. At Mile 6, on a stretch in Prospect Park, 50 friends and family members were waiting.

Mr. Cetner greeted his daughter when she pulled off the race route at 9 a.m., panting but excitedly waving her arms toward the crowd. Mr. Salazar had arrived moments earlier. He waited for the bride, hands on thighs, catching his breath.

Before Mr. Cetner walked his daughter down the grassy aisle, her friend Alexis Schuster handed her a runner’s baton with pink peonies poking out of it. The ponytailed bride tucked a flower behind an ear and joined hands with Mr. Salazar. Hundreds of runners, including many who had noticed the custom “bride” and “groom” running bibs pinned to their backs, shouted and whooped their congratulations while hustling by.

The officiant, Alex Valentine, a friend from Mr. Salazar’s college days at N.Y.U., gave the couple some friendly advice.

“Marriage is a marathon, not a sprint,” she said. “Enjoy the highs and power through the lows.”

After a long kiss, a few smeared tears and a shower of blue-and-white confetti, the bride and groom again hit the trail, side by side.

The couple finished the 13.1-mile race in about 2 hours 45 minutes, a little slow for them. “We usually finish in about two hours,” Ms. Cetner said. “But we didn’t care. We accomplished a lot in those 2 hours and 45 minutes.”