running vs walking

Here is an excerpt from a website:
http://www.straightdope.com/columns/050121.html

Those with a semester or two of physics under their belts reason that since the amount of work involved is the same, running a mile has the same impact as walking an equal distance.

However, this assumes that running and walking are equally efficient means of locomotion. Generally speaking they're not--running requires substantially more energy per unit of distance. Several factors contribute to this. Shall we start with entropy and the second law of thermodynamics? Eh, maybe not. How about aerodynamic drag, which increases with the square of the speed? Probably not something you need to worry about unless you've really been hitting the steroids.

Here's something a little more relevant: Analyses of the biomechanics of walking vs. running suggest that walking is a more efficient gait except at higher speeds. The crossover point is somewhere around 5 mph, varying with the individual. At that speed, walking and running are equally efficient. Below the crossover point, running is less efficient, apparently because you lose energy absorbing the impact of the ground with your bent knees. Above it, walking falls behind because of the awkwardness of the racewalking gait. Gait is the critical issue, incidentally--running speed is irrelevant. Subtracting out the energy required just to keep you breathing, you'll use about the same amount of juice finishing the marathon in two hours or four.

To return to our main point, running consumes more calories per unit of distance than walking. For a person who weighs 70 kilograms (about 154 pounds), walking at 5 kilometers per hour (3.1 miles per hour) consumes 50 calories per kilometer, whereas running at 10 kph (6.2 mph) consumes 78 calories per kilometer

Aha, you say, running is better than walking! Not necessarily, even if we narrowly define "better" as "consumes more calories." When you begin a workout your body is metabolizing carbohydrates, but as the minutes tick by you start burning fat--at minute 50 of light exercise, you're chugging along on a 75/25 fat/carb mix. Sixty percent of your maximum aerobic capacity (reached at roughly 75 percent of maximal heart rate, which is generally calculated as 220 minus your age) is optimal for fat burning; as exercise becomes increasingly strenuous you start burning more carbs. Some have seized on these facts to claim that sustained low- to moderate-intensity exercise is a better way to shed flab than going all out. The point is hotly disputed; I merely note that for the significantly overweight, walking can be easier on the heart, joints, etc