Charles Stalzer has refined his strategy after running more than 80 marathons in nearly 40 years. At age 77, the Alexandria resident can't run as fast as he used to, but he knows what best enables him to complete each 26.2-mile race.

"Caffeine is terrific," Stalzer said. "So I plant Cokes here and there about every five miles or so in little special hiding places.

"Of course," he added half-jokingly, "the problem there is you have to remember where they are."

Unconventional sports drinks aside, Stalzer is one of 99 runners age 70 and older registered for tomorrow's Marine Corps Marathon. For many in this group, what began decades ago as a simple conditioning routine has evolved into a long-lasting, consuming passion for the competition, camaraderie and lifestyle associated with running marathons.

"It has just become part of my life," said Margaret Hagerty, 82, the oldest woman registered for the race. "I just love to compete, and I'm not quite ready to give it up."

The Marine Corps Marathon, nicknamed "The People's Marathon," has a reputation for welcoming inexperienced and slower runners. The world's elite marathoners normally don't participate because the winners aren't awarded prize money. That creates an atmosphere in which older runners such as Stalzer and Hagerty, who expect to finish in six hours or longer, feel comfortable.

The Marines "offer encouragement whether you're an elite runner or a slow runner," said Stalzer, who will run in the 30th Marine Corps Marathon tomorrow, his 29th time running the race. "That was unlike the other marathons I had run in. If you're in the trailing group [in other marathons], you were lucky to even get something to drink in the latter stages of the race." (He ran the first 25 Marine Corps Marathons but missed the 26th after pulling a hamstring while training.)

Stalzer and many of his peers are a product of the running boom that took place in America during the last quarter of the 20th century. As marathoning became more mainstream, not just for elite runners, people began running marathons recreationally. Many of them have continued running into their latter years.

"There is a swing that older runners are doing marathons," said Rick Nealis, Marine Corps Marathon race director. "I think that's part of the acceptance that you don't have to be a three-hour marathoner. You can do it for the experience."

Bob Dolphin, 76, has run more than 350 marathons in the last 25 years and is currently on a quest to run a marathon in all 50 states. He said some marathon organizers have adjusted their age brackets partly to accommodate an increase in the number of older runners.

"A lot of us who started in our middle age continue running as we get older," Dolphin said. "When I first started running, the [oldest] age category was 50 and over. Now, a 60-and-over category is very commonplace."

The Boston Marathon, one of the nation's most popular and competitive marathons, relaxed its qualifying times for older runners in 2003 to accommodate growing interest. In the last 10 years, the percentage of entrants age 60 and older has doubled from 2.2 percent to 4.4 percent.

Like many of the oldest participants registered for tomorrow's race, Stalzer's enthusiasm for marathoning has intensified even as his physical capacities diminish. Seeking a way to stay in shape during his middle years, he stumbled across a New York Times article that suggested certain sports for people of different builds. At 5 feet 7, 140 pounds, it steered him toward running, and he quickly became enamored of the sport.

Other runners close to Stalzer's age boast resumes that could impress even runners in their prime. Hagerty, a resident of Concord, N.C., began running at age 64 as part of her plan to quit smoking. She has since run 74 marathons, including one on each continent -- even Antarctica.

She is so fond of the Marine Corps Marathon that when she earned a place in the Guinness World Records in July for being the oldest woman to complete a marathon on all seven continents, she used it to account for her race in North America.

"People tell me they want to be like me when they grow up," Hagerty said. "It depends on the person's attitude and how hard they're willing to work. I mean, this is not easy. This takes dedication."

Carlton Mendell, an 84-year-old from Windham, Maine, is a veteran of 26 Marine Corps Marathons, according to the race's media guide. He is the oldest registered runner in tomorrow's race, a distinction he also held at the Boston Marathon in April.

A self-described "junk food junkie" to this day, Mendell was about 50 when he decided to shed many of his 210 pounds. He began running and lost 60 pounds in the first year. Since then he has completed more than 160 marathons and ultra-marathons, including a 125.5-mile race in 24 hours while in his early sixties.

"I got hooked on the races," Mendell said. "More than anything, it's meeting the rest of the people at the events and enjoying the camaraderie. The next thing, I guess, is just finishing. Everybody that finishes is a winner. Even those that have trouble along the way, at least they tried."

While Stalzer, Hagerty and Mendell have all slowed significantly with age, Dolphin still expects to pass his share of runners tomorrow. The resident of Yakima, Wash., completed last year's Marine Corps Marathon in less than five hours -- faster than almost half of the 16,399 finishers.

Since his retirement in 1988, Dolphin has averaged about 22 marathons per year. His wife, Lenore, accompanies him to all of his races. He ran a marathon in his 25th state last Saturday in Newport, R.I., as a tuneup for the Marine Corps Marathon.

Barring injury, each of the four marathoners plans to run every step of tomorrow's race. Despite their longevity in the sport, though, they have not avoided the maladies that plague most runners. Dolphin is battling a pulled muscle in his hip. Haggerty is nursing a stress fracture in her right foot that disrupts her stride, which she affectionately refers to as "the nursing-home shuffle."

Minor injuries aren't a significant deterrent, though. Stalzer will strive to finish tomorrow's race in less than six hours, and Hagerty will do her best to cross the 14th Street Bridge at Mile 21 of the course before it reopens to vehicles at 1:45 p.m. And soon after the race, they'll resume their training, running dozens of miles each week to prepare for the next one.

"I know one of these days they'll probably pick me up out of the road," Hagerty said. "But that's all right. That's better than quitting."

Charles Stalzer, 77, plans to participate in the 30th Marine Corps Marathon tomorrow, marking the 29th time the Alexandria resident has run the race. "I'm not quite ready to give it up," said Margaret Hagerty, 82, the oldest woman registered for the race.