It's a bit oversimplified, but substantially true: A 30-minute walk a day helps keep the doctor away.

That's the gist of the 278-page Surgeon General's Report on Physical Activity and Health, issued in 1996, which urged Americans to get 30 minutes of moderate activity on most days of the week. It's also the central finding of a Harvard University study, published recently in the New England Journal of Medicine, which concluded that walking can reduce the risk of heart attacks in women to the same degree as vigorous exercise.

Brisk walking three hours a week can cut the risk of heart disease by as much as 40 percent--equivalent to the benefits of jogging or aerobic dance, reported JoAnn E. Manson, professor of medicine at Brigham and Women's Hospital/Harvard Medical School. More walking equaled more benefit, concluded Manson's analysis of 72,488 women enrolled in the Nurses' Health Study. Women who walked five or more hours a week cut their risk of heart attack in half.

Moderate activity, such as walking, takes a little longer than vigorous activity to achieve a similar result. For example, Manson noted that vigorous exercise like jogging only requires 1.5 hours per week to burn as many calories and get the same reduction in heart disease risk as is conferred by three hours per week of brisk walking.

It's like the old joke about which weighs more, a pound of feathers or a pound of lead.

They both weigh the same amount--a pound--but the feathers will take up more space.

Similarly, a mile of brisk walking and a mile of light jogging both burn about the same amount of calories, but the mile of walking takes longer. Walking, however, has a lower risk of injury. And most important: More Americans are likely to "just do it" when it comes to walking. Easy, inexpensive, practical, low-risk and fun, fitness walking is America's most popular physical activity, with 17 million frequent participants--up from 12 million in 1987.

While walking is one of the best things you can do to boost your health, an occasional stroll through the mall won't do the trick. Like any fitness program, walking must be done regularly for optimum benefit. Here are seven strategies to enhance the results from your daily walk:

* Change it up. The three keys to boosting benefits are "variety, variety and variety," says Mark Fenton, editor-at-large for Walking magazine. Over time, your body adapts to the demands placed on it, he notes, "so once you become accustomed to your routine, you'll need to change it if you want to get over a fitness plateau." Instead of simply walking the same path every day, he says, "go longer, go shorter, go faster, go slower, take a new route, walk with a new person, join a club, walk solo."

* Check your technique. Stand tall and look forward, not down in the gutter. Land on your heel, roll your foot smoothly from heel to toe, then push off strongly with your toes. For a speed boost, bend your elbows to 90 degrees and let your hands swing in an arc from your waistband to chest height. To pick up your pace, take quicker--not longer--steps and let your stride length come naturally. (For more tips, send a self-addressed, stamped envelope to Tip Sheet, Walking magazine, 45 Bromfield Street, Boston, MA 02108.)

* Power up with poles. As great as walking is for the legs and heart, it doesn't do much to strengthen muscles in the upper body. But when you add a pair of trekking poles--which look like ski poles--you'll work your arms, chest and shoulders, too.

"Fitness walking with two poles is a whole-body workout similar to cross country skiing and burns 20 to 50 percent more calories per mile than walking without poles," says Greg Wozer of LEKI USA, which has sold about 750,000 pairs of poles over the past six years. Created to help hiking guides relieve stress on their knees, the poles' one disadvantage, he acknowledges, is "the geek factor."

* Take a hike. Going "off road" adds elements of balance, agility and coordination training to a walking workout. When you hike with a club, "it encourages you to go much farther than you might on your own," says Susan Klein, president of the Capital Hiking Club, which offers day hikes of varied lengths in numerous Washington area locations. "You get away from the city, you have the benefit of an experienced leader and you can be sociable or walk by yourself." (For information about hiking and referral to clubs, call the American Hiking Society at 1-888-766-HIKE or visit the group's Web site, www.americanhiking.org.)

* Head for the hills. Like lifting weights, walking hills is a form of resistance training. But the weight you're "lifting" is your own body. "Tilt your body into the hill," suggests Miami exercise physiologist Bob Greene, author of "Keep the Connection" (Hyperion, 1999). "Keep your shoulders, back and chin up, but pitch your entire body forward a couple of degrees--like being the Leaning Tower of Pisa."

* Speedy does it. "Pick an object slightly ahead of you and challenge yourself to walk as fast as you can until you get there," suggests exercise physiologist Therese Iknoian, author of "The Fitness Walker" (Human Kinetics, 1995) and "Walking Fast" (Human Kinetics, 1998). "When you get to that telephone pole or mailbox, slow down, let your heart and breathing rate come back to a comfortable level, then pick another point to walk fast to." Elite athletes call this "interval training," but Iknoian prefers the term "speed play."

* Walk with someone you love. Walking together is a wonderful way to spend time with friends or family. To promote the benefits of walking and pedestrian safety, a coalition of government and private organizations called the Partnership for a Walkable America is sponsoring "Walk a Child to School Day" on Oct. 6. For more information, call the National Safety Council at 1-800-621-7615, extension 2383, or visit the Web site www.nsc.org/walkable.htm.