Laura Clark hit the trail running years ago and never looked back.

She runs the woodsy trails near her upstate New York home, up Adirondack mountains, and on rollercoaster courses up and down through the Berkshires of Massachusetts.

“It’s much more fun to be out there in the woods, instead of breathing in exhaust fumes,” she said.

Ms. Clark, 58, still runs on pavement but mostly does “trail running,” a pursuit that might sound foolish to the uninitiated – navigating trails full of ups, downs, dips, and rocky bits at jogging speed. Oh, and watch out for slippery rocks and snakes.

But trail runners describe it as a sublime union of exercise and nature. It’s gentler on the legs than pounding the pavement, they say, and more majestic: Imagine a runners’ high at the summit of a mountain rather than on the shoulder of a road.

“More gentle, more beautiful, more fun,” said Barb Ordell of Tallahassee, Fla. “I get a real thrill zipping by trees and jumping rocks on narrow single-track trails.”

Trail running is nothing new. People were dashing through the wilderness well before there were sneakers. Consider the Dipsea, a scenic 7.1-mile race in the San Francisco area, which began in 1905. Other off-road runs are decades old.

But trail running, like so many outdoor activities, appears to be getting more popular. Nancy Hobbs, executive director of the All-American Trail Running Association, said the number of trail events has grown three to four times since the mid-1990s.The association’s Web site now lists more than 1,000 runs a year, most of them in America.

Meanwhile, sporting-goods stores’ shoe racks are giving more space to “trail running shoes” – built light like sneakers, but with nubbier soles – though a portion of these fashionable shoes will never tread on anything wilder than back lawns.

There is easy trail running and hard trail running. Easy could be a three-mile run through scrubland with a soft trail and little hills. Hard would be heading into thin air up a 4,000-foot peak.

The sport is sometimes lumped in with mountain running, which is sort of a tougher, older brother. Mountain running, though, can be done on roads as well as trails.

Some of the most daunting runs in America are mountain runs. Participants in the Pike’s Peak Marathon gain 7,815 feet in altitude to the summit, then head back down. The course for the White River 50 Miler by Mount Rainier rises and falls 17,400 feet.

That sort of wild diversity in courses is why trail runners seem less obsessed with personal times than road runners. Running seven minutes through West End Trail in Bangor, Maine, is different from the Lone Star Hiking Trail in Texas. Even a single trail can be dusty one day, muddy the next.

No matter the conditions, ankle injuries are a big concern for runners because of the unpredictable topography. Runners should watch where their feet are falling, Ms. Hobbs said, and building up your ankle muscles helps, too. On the plus side, runners say the risk of ankle injuries is outweighed by the benefits to knees and arches, which are less likely to develop repetitive-impact injuries.

“The injuries are more dramatic,” Ms. Clark said. “You can fall down and come up all bloody, but you’re not going to get those nagging injuries that road runners get.”

Trail running is not for everyone. Road runners contemplating the transition must resign themselves to a bumpier ride featuring boulders, switchbacks, and 45-degree inclines. And forget about stopping to smell the roses. Still, trail runners insist they can soak in the sights and smells of nature, even at a hustling pace.

“Some people believe that you can’t enjoy the trail when you are running – they are wrong,” Ms. Ordell said. “True, one must focus on the footing ahead, but the senses are hyper-aware.”