Minute for minute, running can burn three times more calories than walking. It improves lung capacity, tones muscles, and strengthens bones. It also can lengthen your life: A 13-year study at Stanford University found that 50- to 85-year-olds who ran about 20 miles a week had a lower mortality rate and developed fewer disabilities than those who did not.

But even short bursts of running mixed into a walking routine will boost your health. In fact, unless you’re training for a marathon, there’s no reason to run more than three or four miles at a time. This guide will help beginners get going and show more experienced runners how to stay on track.

The Starting Line

Once you’re ready to run, suit yourself up with a sturdy pair of running shoes and find a trail. Begin with sessions of no more than 20 minutes and a mixture of walking and jogging every other day, suggests Roy Benson, an Atlanta-based exercise physiologist and running coach. Walk for a few minutes, then step into an easy jog. When your legs start to feel tight and you begin to labor for breath, ease back into a walk to let your body recover. But don’t slow down too much. “You shouldn’t settle back into a stroll — it should be a purposeful walk,” says Scott Cohen, a triathlete and a certified trainer in New York City.

Even if the exercise feels difficult at first, stick with it. “It’s easy for the mind to give up at the first cue of unease from the body,” says Cohen. Remember that next-day muscle soreness is a normal reaction. “Everybody should expect that,” says John W. Robertson, a sports-medicine physician in Seattle.

Cohen recommends that beginners aim for two to three minutes of running followed by five minutes of brisk walking, building up to 20 to 30 minutes of uninterrupted running. Within the first six weeks, “graduate to less time walking, more time running, and then eventually to pure running,” he says.

Until you acclimate, take it slow (even if that means walking for 17 minutes and jogging for three). The most common injuries, such as shin splints, result from doing too much too soon. And don’t push yourself to go faster. “Speed will come as your body adapts to the activity,” Cohen says. After you’ve been running for a couple of months, set a mileage goal. Twelve to 15 miles a week is a good place to start. Ultimately, try to keep your runs to no more than 30 to 45 minutes. Longer times may increase your risk of injury without significantly improving your health.