From a Wall Street Journal online article:
Tuesday, Friday and Sunday, he is out before dawn for a 1.5- to two-hour run with Abby and Finn on one of the many trails accessible from Tucson along the Catalina Highway. The dogs are disciplined enough to run off-leash in a pack with him. The farthest he has taken Abby is a 13-mile, three-hour run. “She came home quite tired, as did I,” he says. When training for a marathon or longer distances, he adds a solo run on Wednesdays. He’ll run up to 23 miles on a network of paths in Tucson called the Loop.
Mr. McLean has had Achilles tendon problems as the result of tight calf muscles, and says he stretches for 15 minutes every night and before his morning run.
Like many marathoners, John McLean trains with running buddies. But if he isn’t keeping pace, he gets barked out. Mr. McLean is a dog-lover who logs miles with four-legged friends, both his own and rescues.
For years Mr. McLean, 63, ran solo. He and his wife, Barbara McLean, live in Arizona. They worked in the aerospace industry and travel made it tough to look after a dog. The day after Mr. McLean retired in 2014, he came home with Abby, a 10-week-old Chocolate Labrador.
To read more: https://www.wsj.com/articles/this-marathoner-is-a-dogs-best-friend-11575201674
They found that these physically active mice had fewer inflammatory cells (leukocytes) than sedentary mice, an effect they traced to diminished activity of hematopoietic stem and progenitor cells (HSPCs). The lower activity of HSPCs was due at least in part to exercise-induced reduction in the levels of leptin, a hormone produced by fat tissue that regulates cells within the hematopoietic bone marrow niche.
The riders who had pedaled on an empty stomach, however, had incinerated about twice as much fat during each ride as the men who consumed the shake first. The riders all had burned about the same number of calories while pedaling, but more of those calories came from fat when the men did not eat first.
In the spring and summer, he trained two to four hours a day, six days a week, running daily and carrying 60 pounds of water up a 4,000-foot peak near his home in Seattle twice a week. “All the research has shown that 80 percent of training for alpine ascents needs to be long duration and low intensity, to build a huge foundation of endurance,” Swenson says. “There are no shortcuts to this. There’s no thirty-minute-a-day gym workout. You have to have the discipline to put the time in.” 
“Another behavior change is physical exercise,” Pillemer said. “A paradox of pain is that exercise helps reduce it, but it’s difficult for people in pain to think about exercising. So they don’t exercise, they get more sedentary and the pain increases; it’s a vicious circle. So how do you get people to actually change their behavior?”
Researchers suggest that intensity is critical. Seniors who exercised using short, bursts of activity saw an improvement of up to 30 percent in 
Now 63, Mr. Peterson has progressed from bike paths to rugged mountain trails and is known for his caped helmet emblazoned with his nickname, UniGeezer. Based on his GPS and bike computer, he estimates he’s logged nearly 30,000 miles, or 24 million pedal revolutions, since he started.
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