In this case, the shared experience of fast times and valiant triathlons taught them nothing. They had their own competitive foundation. What they shared, however, was a common belief that one could be fully invested in a healthy lifestyle, even if they weren’t the fittest of athletes.

Take, for example, 43-year-old business manager Geri Kulash and his 23-year-old son, Jake. On their way to San Diego International Airport this past December to catch a flight home to Los Angeles, Geri noticed some turbulence that prompted him to check into his hotel room. Upon pulling into the parking garage, he spotted Jake on a bike sprinting ahead of him, at least 10 minutes ahead of their 10:30 a.m. departure time.

“As we neared our destination, he pulled off the road to accelerate, and I knew from the look on his face that he wasn’t ready to let me pass,” Geri told me. “I asked him if he was OK, and he said, ‘Yeah, I just didn’t want to stop.’ I asked what his name was, and he said, ‘Shane.’

“That’s when it clicked. A father and son having a chance run-off in the hotel parking lot.”

While they’ve both trained, been raised, eaten, exercised and eaten again and again, Gibran and Jake are poles apart in other ways as well: Jake is active in sports that Gibran isn’t — especially basketball. That gave Geri a chance to motivate the younger Kulash to reach 100 miles, a challenge that Gibran didn’t take lightly. But things were a bit different this time. Geri has just come off an intensive four-day walk, hiking to the top of Mount Fuji, which he did for nine-and-a-half miles in dark blue pants and a green and black San Francisco Giants jersey emblazoned with the number “61” — which is the last number he wore for a professional team, the team he will never play for again.

While he had planned on training for longer, Geri hadn’t anticipated having to stop to travel half-way up his father’s new mountain. Jake, who had missed his flight home to Los Angeles because his mobile dropped, would have to wait even longer in California.

Over lunch in San Diego, Gibran discussed who the first good sport he would be if one of them won. Jake said he would quit basketball, even though it meant that Gibran wouldn’t be able to work out every day. “When I was training, I would feel motivated after a few workouts, but once I finished, I would feel bad for putting so much time into it,” Jake said. “If I won, I would be proud of myself, but, also, I would want to take some time to train for the triathlon. So that would leave me out of the race.”

But the concept of finishing a race and then taking time off is new to Gibran. So, his solution was unconventional — one that involved a maximum sprint of five miles. “I think I was a bit more stubborn,” he said. “I was like, ‘You have to run that full five.’ Jake decided that he would take the road, and he seemed a bit more relaxed.”

After that day, the two had a phone conversation about what happened, and Jake initially felt better about the choice. They then had a more personal talk. In that conversation, Gibran said he learned that Jake had always found himself pushing past his own limits, something that was fueled by a lifelong obsession with science fiction movies, including those by Steven Spielberg.

“I don’t ever want to see an acceleration of Shane again,” Gibran said. “I’m really proud of him and my foundation but at least for one time, we will have to keep pace with him. I will stop when he does.”

About six months ago, Gibran took on a project that was both pragmatic and personal. He asked himself what his life as a runner would be like if he were to quit, deciding to change from a daily run to a three-minute 1,000-meter jog in order to fit into the two other physically challenging events for which he was training: the triathlon in July and the marathon in October.

“I have done amazing things in cycling, in swimming, in walking, but that is not the ultimate challenge,” he said. “Those are fun. I have my bike. But I have never felt more alive and more alive