My ankles ache. My knees won't bend. Who would have thought walking could be so painful? Or challenging?

I've been hiking with the Wanderbirds, a group of hard-core naturalists, ages 18 to nearly 80, who roam the area's national parks every weekend.

They say one reason they walk is to preserve a tradition that began 45 years ago when nature writer Robert Shosteck formed the club.

"The Wanderbirds have a tradition of going somewhere every Sunday," said Ernest P. West, 62. A few years ago that tradition was threatened by a foot of snow. Roads were impassable and the group leader canceled the bus. West said he was summoned to join the hike at Anglers Inn in Great Falls, Va. Twelve people showed up, and they hiked.

"With a name like Wanderbirds, (newcomers) don't expect to find one of the toughest hiking groups in the city, or the number of women," he said. "In the worst weather, you'll find the women will out-number the men every time. People come out to hike because it's a personal thing."

Last weekend, after days of driving rains, 45 people -- many of them women, most of them elderly -- met at the corner of 17th and K streets NW to take a chartered bus to Shenandoah National Park. After paying a $9.50 nonmembers' fee (members pay $8) I rode 2 1/2 hours to brave the humidity and 90-degree temperatures on Rocky Mount Trail, a path true to its name.

At Massanutten Point on Skyline Drive, we set out for Rocky Mount Overlook, the first leg of the seven-mile, 2,000-foot climb of the "short" hike. People going the long route faced a 10-mile, 2,700-foot walk.

Nine people took the short hike.

"I don't think you can sum us up, except to say we all like to hike and we all like the woods. Dave Brownlie has gone the whole length of the (Appalachian) trial, over 2,000 miles," says Martha Lippman, a short, vibrant woman in her 40s. She converses effortlessly as she walks uphill through a lush forest.

The pace is fast, rough in sneakers. No one stops.

Hikers gossip and talk politics. At times silence and trees shroud us in a tight cocoon.

Jake Lowenstern, a Wanderbird three years, leads the group for the third time -- his last before departing for Dartmouth College this fall. Later the Wanderbirds will surprise him with a going-away cake and punch. Among these graying heads and craggy faces, Jake, 18, is the favorite grandson.

"It's good exercise," Jake says. "I've been out in some pretty grisly weather, and sometimes you're hiking for its own sake. I know all the people here and I like them. They're a very diverse group."

"It's much cheaper than playing golf," he adds. "All you need is a pair of boots, rain gear, a light pack and canteen. You've got fresh air, and it's a great deal of fun."

The hikers are sure-footed, scrampering up rocky paths faster than I can walk on level ground. Many of the more than 200 members have a wanderlust that has impelled them to hike in different parts of the United States and other countries, Brownlie said.

Bob Kinsey, 57, a tax legislation officer for the Internal Revenue Service, has another theory about the group's love of hiking.

"Most hikers are looking for Shangri-La, some place beautiful that they haven't been. . . The reason most people hike is to clear out the mind."

Kinsey said the average Wanderbird takes at least 40 hikes a year. Many members are also single, and hiking fills lonely weekends. "I call it the 'Sunday singles syndrome,'" he said.

Howard Fenton, 35, a financial aid officer with the Department of Eduation, came with a friend, Roslin Arrington. It was their first hike with the Wanderbirds.

"They were older than I thought, and I did wonder," Arrington said. "But I really have a lot of respect for them. I was dead when I got to the bus, and this woman in her 60s went on the long hike."

At the top of Rocky Mount Overlook, hikers perched in trees and huddled on precipics to eat lunch. Hawks soared against a backdrop of hills.

Alice Ruddiman, a retired officer worker in her 70s, quit horseback riding in 1968 to hike. She wanted "to keep myself from falling apart. I sort of picked it out of the paper.'" Her first hike was with the Wanderbirds, "straight up the mountain. It nearly killed me. From then on, I was hooked."

She went on the famous 15-mile "ice hike" two years ago on a snowy trail in West Virginia. "It was the most fantastic thing. We were down on our rear ends, our fronts, we slid all over the place." Still they hiked Ruddiman wondered why.

" i guess," she said, "you have to be crazy enough to want to go out and extend yourself."