With trail running, it's a tight race between the physical benefits and the mental payoffs. "I get really joyful when I'm out running amidst the trees in the elements and don't have to hear cars," says Meghan Arbogast, a marathoner who qualified for the 2004 Olympic trials and is the coach of the Mac Forest Mud Runners in Corvallis, OR. "Physically, trail running makes you stronger than running on the road or treadmill because it works the small ‘balancing' muscles in your hips, groin and ankles. And because the impact is less than on pavement, you can run longer without injuring your joints."

Before you head out, a few pointers:
> Wear a pair of trail running shoes, which provide more traction than road shoes. Trail shoes also have a lower heel, allowing you to stay closer to the ground and giving you more "feel" for the varied ground underfoot. If you live in a wet climate or run outdoors year-round, opt for shoes with waterproof Gore-Tex in the uppers.

> Plan ahead in terms of hydration and fuel. If you do get lost, you don't want to be stuck without water. It's also smart to carry a whistle if you're running in an isolated area.

> Know that your speed is slower on trails because the softer surface doesn't provide as much energy return as pavement or sidewalks. It's best to run for time instead of mileage on trails: Run for 60 minutes instead of trying to figure out a seven-mile route.

> Don't consciously modify your stride too much, although you'll want to lift your feet slightly higher to prevent tripping over obstacles like rocks and tree roots, suggests Tina Vindum, founder of Outdoor Action Fitness and a personal trainer who leads clients on running workouts in wooded Marin County, just north of San Francisco, and in San Francisco itself. "Also, don't look at your feet; instead, look ahead about 10 to 15 feet. Your brain ‘records' upcoming terrain, so it knows what is underfoot."

> Pay attention to your surroundings and remember that things can look different coming back than they did going out. ("I don't remember seeing that fallen tree/stream/boulder.") Arbogast suggests going with a "trail guide" running buddy on your first few outings. Two online options for finding running trails in your area -- www.trails.com and www.traillink.com.