Last winter, Jennifer Sanford was sitting at her desk at MassMutual in Springfield where she works as a trader, when an e-mail message came across her screen. The message gave the details of an upcoming triathlon to be held later that summer on Martha’s Vineyard. Ms. Sanford had never entered a triathlon or a race really of any kind before and so it wasn’t the competition that first caught her eye. It was the date of the race: Sept. 11, 2011.

The race had not been billed as an event to honor the 10th anniversary of 9/11, but for Ms. Sanford this was exactly the feeling she had. She was one of the first to sign up.

Training in the Vineyard Waters has healing effect. — Patricia Roberts

In September of 2001, Ms. Sanford was in between jobs, having worked for years at Lehman Brothers in New York city and about to begin a new job on Oct. 1 at Jefferies in Stamford, Conn. The weekend before 9/11 she had taken her two small children, Alex, age eight, and Christian, age six, on a Circle Line boat cruise around lower Manhattan.

“I was a working single parent so I would always visualize stuff for them,” she said, remembering that day as they cruised past the Twin Towers. “I’d say, that’s where mom works, and they were so proud on the Circle Line and we took tons of pictures of the towers.”

A few days later, while at home in Westchester, she received a call from her sister, Patti Roberts, to turn on the television. Her first thought upon seeing the planes hit the towers was that of a trader, her career for close to 30 years.

“I called up my good buddy who was an economist at Texaco in White Plains and he manages oil for them and I said you need to sell everything you have because the world’s about to shut down.”

Then she tried to get her kids.

“But it was impossible,” she said. “They were kept at school until the end of the day. They [the school officials] tried to make it normal for them. I think they were trying to figure out whose parents were dying and who didn’t have parents to go home to, so they didn’t want to release the kids.”

It was a scene that played out all over the suburbs of New York, New Jersey and Connecticut, where so many of the men and women who worked in the World Trade Center lived and raised their families.

Two weeks later, when Ms. Sanford began her new job at Jefferies, her employer greeted her with “a face mask and a water purifier and all kinds of emergency strategies.

“They sat me down in a chair at a trading desk and there was an empty chair next to me and I said, ‘Whose is this?’ And they said, ‘It’s Mark’s.’ And where is he? ‘Well, Mark went to three or four funerals a day for about two months and he never came back to work.’ It was all around you. Wherever you were. I lost a lot of friends that day.”

She also lost family.

Ms. Sanford’s brother in law, Frank Piacentino, worked at Cantor Fitzgerald, a firm that occupied the 101st to 105th floors of One World Trade Center.

“He was at work that day,” Ms. Sanford said. “He called his wife and kids and talked to them before he died, but he was on one of the high floors.”

In deciding to train for the triathlon, Ms. Sanford felt that she really had no other choice.

“It just felt like I’m meant to run and be grateful for the energy and health and life and figure as much suffering as I really think it’s going to be, which it is, you don’t know how many days during the training I feel like I can’t do this, honestly, I feel the thoughts of these people I knew individually.”

The Vineyard Warrior Triathlon is an Olympic distance race with a one-mile swim, a 24.6-mile bike ride and a 6.2-mile run. Much of her training has been done on the Vineyard, a place that has always been special to her but after 9/11 became a sanctuary for her entire family.

“It was after 9/11 that my parents bought the Ivy Cottage [in East Chop]. They had this urge to spend time with their family and so they sold stocks and bought this house and pretty much gave it to the kids to share — build it and they will come. For my children the Island became a refuge. They would ask me in New York what would happen, where will we go because we were right near the nuclear [facility] in Indian Point so there was a lot of uncertainty, but the one thing that helped them, I would say, we will go to Martha’s Vineyard.”

The swim part of the race which can be the most difficult or frightening to many participants has been eased thanks to the waters around the Island. “It’s been the best part of the training, getting in the Vineyard water,” she said. “I miss it when I’m here back at work. And then there’s the 24.6-mile bike ride which I’ve done growing up around the Island and the 6.2-mile run which is kind of in my back yard. I call it my healing run. It’s that loop around East Chop.”

But still it hasn’t been easy for a single, working mother — her boys are now 18 and 16 — trying to fit in all the training between work, car pools and other responsibilities.

“My sister, Patti Roberts, has been my biggest fan. She’d pull me away from work, laundry or cooking to push me to run or swim. She had me swimming in the morning a mile, then again later that afternoon another mile. In the beginning, I was a bit timid of the swim in the ocean, especially if no one was around on the beach or water. She’d walk along the shore for my whole route . . . cheering me on and reassuring me that there were no sharks.”

There were injuries, though. Last May, while training, Ms. Sanford broke her ankle. In July, she re-injured it.

“I went to physical therapy and pushed them, ramping up on massage and they just go and put my joints back together. I’m driven to do this. I’m not going to fight it,” she said.

There is also the matter of her birthday. On Sept. 12 she will turn 50. Which means the day after 9/11 she turned 40.

“My birthday has never been the same, but this time, for my 50th it feels different. It’s progress for me. It’s a page turner in my life,” she said.

Ms. Sanford will have plenty of fans cheering her on this weekend, including her family and even a group of friends from high school.

“I have a group of us who reconnected from high school to celebrate everyone’s 50th,” she said. “They’re scattered all around the country and for everyone’s 50th we get together for dinner. And they are all coming to cheer me on.”

And about race day, even with the support of family and friends, how does a novice keep it together in order to finish the race? Again, it goes back to 9/11.

“It’s going to be a mental race for me. Literally, that’s my race strategy, to think about these people.”