Motivated when she read about a trail-running trip to Machu Picchu in 1999, Kirsten Poulin headed for the Southern California hills to give it a try. The former hiker was instantly hooked. Since then, she’s run along mountain trails from the West Coast to South America, and has even penned a book on the sport. “Living in the city,” says the mother of two, “it’s a very good way for the mind to get free.”

Poulin’s not alone in her passion. Between 1994 and 2004, the number of trail runners in the U.S. grew by 26 percent, according to a study by the Outdoor Industry Association.

BENEFITS  Hikers understand the beauty of being in remote areas, says Poulin, but as a trail runner, “you get to see twice as much.” And then there are the endorphins: “It just magnifies the whole hiking experience,” she says.

As they negotiate uneven surfaces at increased speed, trail runners develop more overall strength and balance than hikers or pavement-bound runners. Poulin notes, “I’ve been clumsy all my life and this has made me much more coordinated.” And mindful to boot. You simply can’t zone out as much while trail running.

Reaching a frequent anaerobic state also helps to burn up lactic acid and build muscle. And, because you’re jumping streams one minute, and ducking branches or scrambling down scree the next, you’re less likely to incur the repetitive motion injuries road runners do.

GETTING STARTED  Poulin suggests keeping it to two short trail runs per week (an hour or less each) in the beginning. Think time, not mileage. Choose a fairly smooth and not-too-hilly trail you’re already familiar with, she adds. Forest service roads and gravel bike paths are safe bets—just make sure springtime mud has dried before you head out. The more relaxed your mind, the easier it’s going to be for you to focus on running rather than on wondering, “Where the heck am I?” Treadmill or other cardio workouts will help strengthen lung capacity, and you can develop your quads and hamstrings—and get used to hills—by cranking up the machine’s incline/decline. Get the lower legs and ankles ready for action with easy runs on gravel roads, calf raises, and work with weights. Yoga also helps improve flexibility and balance, Poulin says.

WHAT YOU NEED  In Poulin’s CamelBak hydration pack (she carries three to four liters of water), you’ll find several packets of GU, a small first-aid kit for cuts and scrapes, a cell phone if she’s going solo, sunscreen, an emergency blanket, and trail mix. Runners in the Northeast might want to throw in a windbreaker, extra socks, and a cap for sun or rain protection.

And then there’s the footwear. Trail running shoes are, on the whole, more flexible and breathable than hiking boots, weigh as little as eight ounces, and have a serious tread designed for traction in a multitude of conditions. Definitely lose your old running shoes—with more support, reinforced outsoles, and waterproof Gore-Tex liners, a proper trail-running shoe will better support your ankles and protect your feet from rocks and stream crossings.

LEARNING CURVE  Expect a few scrapes and ankle rolls as you learn to navigate. If you’ve been a road runner, Poulin warns, you may get discouraged as you find you move about 20 percent slower on the trail, but your pace and footing will improve with time. Don’t worry about going a little slow at first—after all, the views will be a whole lot better than they are from the pavement.