The idea came to him one day while passing the time away in his self-described man cave.

Keith Clemens, a Merrill Lynch senior financial advisor from Alpharetta, was nearing his 50th birthday and during a moment of self inventory wondered if he'd been able to fulfill some of the promises of his youth and particularly had he been able to avoid becoming the middle-aged fat guy.

The answer, of course, was no.

But as his birthday approached last January, Clemens wanted to do something that would somehow validate -- his word -- the promise.

"What can I do that sounds crazy to most people but I can still accomplish?" he asked himself.

His answer? Run one marathon a month for a year.

For most of his life, Clemens had enjoyed being physical, running, playing, you name it.

He was a member of the Ansley Park Running Club and enjoyed playing squash several times a week. He'd run five marathons before and countless half marathons so he was already in relatively good shape.

To reach his goal, Clemens stepped up his game, training almost daily at the Midtown Athletic Club at Windy Hill. To help build his endurance and muscle, he strapped his 30-pound son, Austin, to his backpack.

As his dad scaled 30 flights of stairs, up and down three, four times, as he jogged around the running track and participated in Midtown's spinning classes, 3-year-old Austin traded fist-bumps and high-fives with the club members they passed along the way.

A self-described late bloomer, Clemens got married at 48, and had his first child soon after. Friends swore, he said, that marriage and a kid would slow him down. He'd surely become an old, fat guy like the rest of them.

To prove them wrong, Clemens simply brings Austin and his wife Dana along for the ride.

By January he was ready for his first marathon: Callaway Gardens.

Instead of taking Austin along for the 26 miles, Clemens packed two video cameras in his backpack. He wanted to document the colorful characters whose paths he'd cross during each event.

"I was only interested in finishing each race so I began to film people along the way," he said. "To me, it was a much more rewarding process."

Clemens was fascinated with the runners he met -- cancer survivors, war amputees, and formerly overweight people, each of whom had their own stories, personal reason for competing.

"Each person's story was one of growth," he said. "There was a guy, for instance, with one leg from the Afghanistan conflict and I met a woman with one leg who was a cancer survivor."

In addition to filming fellow marathoners, Clemens, who dubbed himself the "Marathon Man," also chronicled each journey with blog posts at www.keithmarathon.wordpress.com.

"I felt like Charles Kuralt going across America," he said.

"The greatest benefit of a non-race attitude is the opportunity to chat and film fellow runners," he wrote on Jan. 30 after his run at Callaway Gardens. "Each has their own story: there was Gail from the Bahamas. This was her 125th marathon, and we called her "American Idol" because she sang (too loudly) for the first 10 miles. Then I met a Brit with whom I ran from Mile 4-18. She, too, had crossed age 50. We spilled forth about our lives, and despite the highs and lows, admitted that we were happier at 50 than 20. At Mile 18, we both -- without apparent cue -- reached for our headsets and separated, the conversation seemingly complete and satisfying."

In February, he headed to Ft. Lauderdale. In May, he ran in the Georgia Publix Marathon, then Chattanooga and Duluth, MN.

"The Chattanooga Marathon was my first trail marathon," Clemens wrote in May. "It is a beastly thing of narly ruts, cracked granite obstacles, and fallen trees. The upside to the necessary fixation of watching your feet, for fear of tumbling off the mountain is that time is truncated."

The highlight of the year, he said, was completing The Pike's Peak Marathon which starts at 6,500-feet elevation and climbs to 14,114 feet.

"Even trees do not live that high for lack of oxygen," Clemens said.

In between each race, he and Austin trained, running 40 to 60 miles a week. Asked how his body held up to the physical demands, he gave a nod to good genetics and a post-race margarita.

He started with the goal of running one marathon per month. In fact, he completed the goal in 11 months, ending the year with Chicago Oct. 9, Atlanta Oct. 31 and a week later New York,  November 6.

In his last blog post: Clemens wrote: "What started as a physical challenge to validate the promise I made to myself as a young man -- to stay fit -- turned into a satisfying spiritual lesson on life as I met the best in humanity."

Clemens said that he discovered that talent was far less important to accomplishing one's goals than the courage to take the first step, consistency of action and the passion for what you're doing.

Last week, Clemens and Austin were back at Midtown training for his next adventure: climbing Mount Rainer and Mount McKinley, the highest peak in Alaska's Denali National Park.

"I'd like to go to Everest base camp but not sure I want to try to climb it," he said. "It's 25,000 feet and above that people die and I have a family."

Speaking of family, Clemens said topping this year's to-do list is something that might be a little less taxing, a brother or sister for little Austin.