Like jogging, bicycling, swimming, skating, and cross-country skiing, walking builds aerobic capacity. Walking is an aerobic exercise -- a sustained, repeated, rhythmic workout for large muscle groups. This type of workout requires oxygen and depends on the cardiovascular system to supply this oxygen to the muscles while they work.
In contrast, in anaerobic exercises, such as weight lifting or sprinting, the muscles are involved in short bursts of highly intense activity, and they can obtain energy through a chemical process that does not involve oxygen.
Walking at a brisk enough pace offers aerobic benefits by "training" your heart, lungs, and skeletal muscles. Like all muscles, the heart becomes better conditioned the more it is used. By engaging in regular aerobic exercise, you improve your heart's ability to pump oxygen-rich blood to your muscles.
You also make your muscles more efficient at using oxygen, so they can do more work without putting as great a strain on your heart. By increasing your aerobic capacity, you make more oxygen available to your body. You'll be able to exercise longer and harder, enabling you to burn more calories during your workouts.
Michael Pollock, Ph.D., director of the University of Florida's Center for Exercise Science, pioneered research on walking's effects on aerobic capacity. He found that walking, jogging, and bicycling all boosted aerobic capacity to the same extent -- provided they were done at the same intensity. (The walking group sustained the fewest injuries and had the lowest dropout rate, however.)
It is possible to walk at such a high speed that you equal the aerobic conditioning benefits of jogging. But at usual walking speeds, walking is less intense than jogging, so you've got to walk longer -- or uphill -- to get the same training effect as you would get by jogging. Another alternative is to use weights -- hand-held weights or a backpack -- to increase walking's training effects.
For effective aerobic conditioning, you need to walk for a minimum of 30 minutes at least 3 times a week. And during each walk, you need to work hard enough to get your heart rate into your "target range."
There's a catch to increasing your aerobic capacity, though. The more fit you are, the faster you must walk to improve your fitness level. This means walking briskly -- at least three miles an hour, for most people, and four or more for those already in good shape.
It's long been assumed that people who have already worked themselves from low or average fitness into top condition can't get any fitness training benefits from walking. But Dr. Pollock found that when fit people walked briskly for 40 minutes, four days a week, they could reach a heart-rate range of 70 to 75 percent of their maximum heart rate reserve -- close to the results seen with jogging.
The difference: If you walk, you need to increase the frequency and duration of exercise to get the same aerobic conditioning results as jogging.
James Rippe, M.D., director of the Center for Health, Fitness and Human Performance at the University of Massachusetts Medical School in Worcester, has made similar findings. Based on his studies of hundreds of walkers, he says even the fittest individuals can raise their heart rates to 70 to 85 percent of maximum, just by walking. But they have to walk fast -- as much as six miles per hour -- or uphill.
When aerobic conditioning is achieved, it can have important long-term health benefits, including protection against coronary heart disease and stroke. In a Duke University study of 3,000 men, the least fit men were about three-and-a-half times more likely than their healthy counterparts to suffer a fatal heart attack or stroke during an eight-and-a-half year follow-up period.
There is a limit to how much exercise can improve one's aerobic capacity, though, says Ronald LaPorte, Ph.D., associate professor of epidemiology at the University of Pittsburgh. An exercise program can increase a person's aerobic capacity by 30 percent at most.
The remaining 70 percent of the aerobic capacity is dictated not by your activity level but by your genes -- for such things as lung structure and heart and body size. Because of these variables, it is possible that the aerobic capacity of 2 different people may differ by as much as 200 percent.
Walking is a low-impact aerobic exercise that is often recommended for pregnant women, and to ward off the risk of injury. Learn more in the next section of this article.
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