So you’re sitting at home watching the Boston Marathon – or even watching it somewhere along the race route, whether in Wellesley or BC or Copley Square – and you look at the sea of people coursing 26.2 miles and you wonder, with all due respect to Jerry Seinfeld, “Who are these people?”Actually, the folks participating in a 113-year-old athletic tradition aren’t that much different from the people watching it. Take a random sample (OK, two people) from two local communities. Lisa Torchiana of Nahant works as a registered nurse, while Sean Bagley of Lynn is a police officer.From MGH to the MarathonTorchiana has worked at Massachusetts General Hospital for, she said, “20-something-odd years,” which is about the same amount of time she’s been running – “maybe even longer, 25 years,” she said. Three years ago, Dr. Larry Ronan of MGH suggested she combine, with all due respect to Robert Frost, her avocation with her vocation by doing something she said she had always thought about participating in, but never had up till then: The Marathon.”(Dr. Ronan) kind of encouraged me,” Torchiana said. “(He said) if I wanted to run, I could. I would just have to put time and effort into it. I started following a program to run it, and it worked.”Torchiana, a Saugus native, completed her first Marathon in 4:10, running to raise money for Dr. Ronan’s charity, Team Durant, which is named in memory of former MGH doctor Tom Durant. She described the organization as one that sends medical care to troubled areas of the world. She will run for Team Durant again this year.Perhaps just as big a challenge as competing in a Marathon was gearing up for a second one. Three years have passed since Torchiana ran the Marathon for the first time.”I think the main thing is that it takes a lot of time to train,” Torchiana said. “Four months. You live around your running schedule. Doing that every year is not what I wanted to do. I started to train one year, got to mile 15, 16, and decided I didn’t want to do that.”It took the approach of a milestone to motivate Torchiana to run a second time around: She will turn 50 in September. Peer pressure helped. Her fellow Nahant runner, Dawna Nocera, who was profiled in these pages a year ago, turned 50 this year.”Her qualifying time is 4:05,” Torchiana said. “Mine is 4:00. I have to run five minutes faster to qualify than she. I don’t think that will happen.”I usually, for the most part, run with her and a few other pals. I talk the whole time – about kids (she and her husband David have two children), life, being busy, just the usual.”We kind of encourage each other. We run really well together. Our kids are about the same age. We talk the whole time we’re running.”In 2006, David and their children showed up to watch. (They all met at the Colonnade afterward.) This time around, her husband will be on a golf trip and their daughter will be on a school trip.”I’m on my own this year,” Torchiana quipped.But thanks to a milestone and MGH, she’s back on the course after a two-year absence.A detail in Hopkinton, Mass.Sean Bagley works in Everett these days as a police patrolman. But he lives in Lynn, and that’s where his roots are. He graduated from Lynn English in 1989, playing soccer there for a couple of years, and after college at Salem State, he spent eight years on the Lynn Police Department.Nine years after his high school graduation, he ran his first Boston Marathon. He has run the race seven times. He’s run in races in other parts of the country, such as Chicago, Sugar Loaf (ME), and Virginia. In October 2003, his running career took on an international aspect when he competed in a race in Dublin, Ireland.”I always wanted to go,” he said of the country, where he has some distant relatives. “It was beautiful. I can’t wait to go back.”His best time came two years ago at Sugar Loaf, where he finished in 3:20. His qualifying time for Boston this year is 3:15.”A 3:15 or better, and I’ll be happy,” Bagley said.He started tr