Is the fitness benefit of speed-walking the same as that of jogging?
— Sandra Christianson San Ramon, CA
Walking has a lot going for it. Provided you swing your arms and walk at a pace like you have somewhere to be, it can raise your heart rate so that your body is burning stored fuel, but keep it low enough that it can do so primarily through your oxygen-assisted fuel system. (People used to call this the fat-burning zone, but we burn all sorts of fuels all the time.) In other words, with a good walk you work out hard enough to build your cardio-respiratory health, and easy enough to do it for a long time.
Fitness walking is also easier on the knees, hips, and ankles than running. For this reason, walking is also a more sustainable way to get your cardio training —you aren't likely to get injured and don't need to invest in a lot of workout clothes. (Though one could argue that the only really sustainable approach to training is to change your workout every six months or so to avoid burnout and keep you body responding.) Plus, with the arrival of the marketing gimmick/fitness trend known as Nordic Walking—where you undertake fitness walks with specially designed trekking poles—walking looks to become only more popular.
But time, not energy, is usually the limiting factor when it comes to both walking and jogging (as opposed to running), and you can generally work your aerobic pathway harder by jogging. Moreover, walking tightens your hamstrings more than running. People might also underestimate, in this day of no-impact elliptical trainers, the importance of weight bearing movements in exercise when choosing walking over running. Running offers up to four times the weight-bearing impact of walking. While those carrying, say, 200 pounds, are wisely protecting their knees in going low-impact at the outset, one of the best things you can ask of your body is to learn to accept weight-bearing impacts in ways for which it is designed. Like weight training, running strengthens supporting muscles and improves coordination. It also beneficially stimulates bone strength (more so than walking), postponing the onset of skeletal shrinkage and fragility in your later years.
Paul Scott is not a personal trainer but he plays one in magazines. Being as how standards for the profession vary so much, and how he reads far more than a writer can expect to have to read about a subject like training, he thinks that is OK. A health and fitness writer for Outside for about six years now, he is the author of Outside's National Magazine Award-winning article series "The Shape of Your Life," which he is currently trying to fashion into a book of some sort. We all want to cover our butts, so here Paul will try to cover his: Nothing said here should overrule the advice of your doctor. Use your judgment at all times, both in the gym and out. Look both ways before crossing the street. And if you have reason to wonder, ask your doctor if it's OK before starting any workout program. We all want you to live a long, healthy life.
Walking has a lot going for it. Provided you swing your arms and walk at a pace like you have somewhere to be, it can raise your heart rate so that your body is burning stored fuel, but keep it low enough that it can do so primarily through your oxygen-assisted fuel system. (People used to call this the fat-burning zone, but we burn all sorts of fuels all the time.) In other words, with a good walk you work out hard enough to build your cardio-respiratory health, and easy enough to do it for a long time. 
