Eos, the Greek goddess of dawn, took a mortal lover, Tithonus. She asked mighty Zeus to grant him immortality, ensuring herself an everlasting plaything. He did. But Eos forgot to also ask Zeus to grant her tender vittle agelessness. So poor Tithonus got older and older, smaller and smaller, and became less and less appealing. Eventually Tithonus turned into a cricket.

Most of us want to keep running for our entire mortal lives. But age is a greater foe than the fiercest of the Greek gods. While I’m not yet nearing insectitude, I realize that if I want to keep enjoying my running, I have to look for different kinds of challenges. Many of my runner friends have been turning to triathlons to spice up their athletic lives. I would do that, except for the swimming and biking parts. Doing longer races means you don’t have to run as fast, and that’s always nice. But there’s something else I’ve found that has given me more pleasure, and meaning, than any other running-related activity.

This past year I was fortunate enough to be tapped for the Clif Bar Pace Team. We are a group of nearly two dozen people, from various and diverse backgrounds, who lead groups at marathons. We carry wooden dowels with balloons (yes, I know, there must be a better way — no one has come up with it yet) to goal times ranging from 3:10 to 5:30. We are divided into East and West Coast teams; we meet up to six or seven times a year to work together at a marathon expo booth, have meals, go for runs, and get updates on each other’s lives, work, and families. Sharon can always be counted on to have whatever anyone has forgotten; Scott bakes chocolate chip and Snickerdoodle cookies for the group; when Michelle and I room together, we stay up too late talking. Itıs fun to be part of a team.

But the real fun is the pacing. At the expo, we sign people up and give instructions on where to find us on race morning. We answer questions—about training, marathoning, nutrition and hydration. We caution first-timers about picking a reasonable goal. We introduce ourselves and say we look forward to running with them. And we do.

We are volunteers. We give up our time and energy — for a handful of Clif Bars, uniforms and shoes from Pearl Izumi, and a fancy Polar watch — to pace at about 30 minutes slower than our typical marathon times. We do not get paid, though our expenses to the races are covered. We are mostly loud, extroverted, enthusiastic people who, while we each have our own running goals (and in fact, two of our pacers are top ultrarunners who compete internationally), love to help other people meet theirs.

We are allowed to be plus or minus two minutes at the halfway point, and must finish no more than two minutes fast at the end. Our balloons have our finishing times on them. That’s what we’ve committed to run, and that’s what we run, regardless of what happens in the group. Many of my teammates are able to finish within seconds of their projected time.

Generally we start off with hordes of people around us. Since we tend to pace at big marathons, often, at halfway, we still have big groups. Inevitably, at mile 20 or so things begin to thin out. When I paced the 3:50 group at the New York City Marathon last year, I was demoralized to have none of the women who started in my group finish with me. At the Los Angeles Marathon, a big guy who was running right near me said, as I was rhapsodizing about the joys of In-N-Out Burgers, that if I got him to the finish in four hours, he would buy me a big bag of them. I said that I would be there; he just had to stick with me. I ended up buying my own burger.

Sometimes people will join us later in the race. At around mile 18 in L.A. I met up with two girls. They told me weıd be running past their houses in a few miles, and then, soon after that, the Marlborough School, where they were juniors.

I asked them about their college applications and when they answered, I told them that this was their lucky day: I am a high-priced college admissions consultant. If they stuck with me, they could get hundreds of dollars of free counseling. We talked about SATs, recommendations, and which topics to avoid for the essay. At mile 23, I told Christina — whose longest run had been eight miles — to go ahead; we were slowing her down. Celia finished with me, in 3:58, ready to apply to Harvard.

At the Salt Lake City Marathon in June, I met a 61-year-old guy named Jim at the expo. He needed four hours to qualify for Boston. A retired Forest Service guy and Vietnam Vet, Jim was chatty for the first 20 miles. As he got quieter, I just kept on blabbing. I told him that I wanted him to meet me — I demanded that he meet me — in Boston and bring me a potato from his home state, Idaho. I’m looking forward to collecting it on the third Monday in April.

Each pacer has an arsenal of stories about why he or she loves to pace. One of my favorites is from Scott, the cookie-maker. One guy, he said, had been with the group for most of the race, but had fallen back a bit the last few miles. After Scott crossed the finish line, he congratulated the runners in his group, and then waited around, as we all do, to congratulate the runners who had fallen off the pace. He saw the guy cross the line and went to shake his hand. The guy said, “That is not going to do it,” and he gave Scott a big bear hug and planted a kiss on his cheek. “I don't remember his name,” Scott says, “but I will never forget his face.”

A thank you and a kiss. A potato. Much more compelling than a PR or a Shiny Metal Object.

Rachel Toor, a former editor at Duke University Press, is enrolled in the M.F.A. program in creative writing at the University of Montana. Her most recent book is The Pig and I: Why It’s So Easy to Love an Animal, and So Hard to Live With a Man (Hudson Street Press, 2005; paperback edition from Plume, 2006).