Rob Fitz knows the exact moment he decided to run the Marine Corps Marathon.

It was Sept. 26, 2001, at 11:20 a.m. -- the date and time of his mother's death.

"We were in the hospital," Fitz said. "My dad and I made the decision to take her off life support. I had that moment of clarity: I'm not going to be able to run this marathon with my mom. I'll never be able to do it with her, and she always wanted me to. It was that moment that I made that decision."

Barbara Fitz, an accomplished and enthusiastic runner, ran the Marine Corps Marathon 10 times. Each time she ran it, she asked her son to run it with her. Each year, Fitz found a reason not to run.

Then his mother died.

Now three years later, after giving up smoking and losing 50 pounds, Fitz will run the Oct. 31 marathon. Although his mother won't be running next to him, the 32-year-old Virginia Beach resident expects her spirit to fortify him over the 26.2 miles.

Her friends and family remember Barbara Fitz as a devoted Army wife and loving mother to three children. She enjoyed gardening and owned Green Mansions Florist in Centreville.

She also loved to run and took it very seriously. She ran ultramarathons and at one time was ranked among the top 10 in her age group in the Washington area. Along with her husband, Bob, she helped found the Mount Vernon chapter of the Hash House Harriers, a raucous club of hard-core runners. When she coached her daughter's high school track team, Barbara Fitz usually ran faster than her daughter.

But more often than not at races, her compassion overtook her competitiveness.

"She discovered it was kind of fun to hold back, run toward the back of the pack and just find runners who are struggling and run up to them and give them encouragement," said Bob Fitz, who has run four Marine Corps Marathons. "When I would run, I would think, 'I hope someone comes up and does that to me because I'm always suffering.' "

Barbara Fitz encouraged everyone to run: her family, her friends and even people she hardly knew. Almost all were swayed -- except her son, Rob.

"Every time she ran the Marine Corps Marathon she asked me to do it with her," Fitz said. " 'You've got to do it with me next year. It's my favorite one.' I always had an excuse. I'm fat. I'm out of shape. I picked up smoking in college. There's no way I can run a marathon. Run with my mom? How embarrassing. There was always some reason. But I always told her I'd do it with her some year.

"I watched one of my sisters do it with her. I watched my dad do it with her. I watched my sister's husband do it with her, her friends, and I never did it."

Barbara Fitz's leukemia was diagnosed in 1998. She died three years later at age 56. Suddenly, there was no next year for her son.

"Right before my mother passed away, she had a final talk with all of us," Fitz's sister, Lisa Fitzhugh, said. "He made a promise to her that he would change, and he keeps his promises. . . . He's not going to listen to anybody else tell him to do it. But once he puts his mind to it, he'll do it."

Fitz put down his cigarettes in November 2001 and never took another puff. He joined Weight Watchers in 2002 and lost 50 pounds. Last February, he began running.

Initially, his goal was to run three days a week. He next wanted to run a mile without stopping. Eventually, he went faster, then farther. In September 2003, he completed a half marathon.

"It wasn't a spectacular time, but I finished," he said. Then he decided he was ready to attempt his mom's favorite marathon.

Training hasn't been easy. There have been low moments when Fitz doesn't think he can run another step. That's when he thinks of his mom.

"When she went through her first round of chemo treatments, she came out of that hospital and ran two miles at Fort Belvoir around the golf course," he said. "I did it with her. This was before I lost weight, and I was still smoking. I was just miserable. But I thought about how my mom just went through chemo, how bad must she feel but she's still out here doing it. It makes me laugh, and I just keep moving."

When the Mount Vernon Hash House Harriers learned that Fitz was running in his mother's memory, they rallied. Some of them will run with him. Others will cheer along the course. Most have never met him, so they ordered a fluorescent orange shirt for him to wear so they can spot him. It reads: "Rob Fitz, son of Snow Fairy." Snow Fairy was his mother's nickname with the Hashers.

"No, I don't know him," said Sean Lee, one of the Hashers. "But I know his mother. I know his father, and I just think this is a wonderful thing that he's doing."

One of Barbara Fitz's enduring legacies was her positive outlook.

"She would run her marathon or her 50-miler or her 100K," Rob Fitz said. "We would have to hold her up and put her in the car. 'How are you doing, Mom?' She'd look up at us, smile and say, 'Well, my thumb doesn't hurt.' "

It is that saying that sustains the Fitz family.

"No matter how bad it is, if you can put your thumb up and smile, then you're okay," Rob Fitz said. "I know that running 26 miles is painful, but you know what? I bet my thumbs won't hurt."

Rob Fitz holds a portrait of his mother, Barbara. Fitz will run the Oct. 31 Marine Corps Marathon in her memory.