By Rick Morris
A line has been drawn in the sand. We’re squaring off— choosing up sides. A major battle is beginning. Well…maybe not. But there’s a debate going on in the world of exercise. For years fitness enthusiasts have believed walking and running burned the same number of calories per mile. This old school thinking says no matter what speed we move, we’re expending around 100 calories per mile when moving over level ground. If you crawled one mile you used up 100 calories. Did you just sprint a mile? You still burned 100 calories. We believed this because it’s what we’ve been told for years and years. Since we’ve been told this for so long it must be correct, right? Not necessarily.
Blame It On Sir Isaac Newton
The study of exercise and human movement is just like any other science. It’s a work in progress. We’re always discovering new information, making some accepted beliefs outdated. Don’t forget we used to think the world was flat. Aristotle dispelled the myth of a flat earth. This confusion over calories can be blamed on Sir Isaac Newton. It’s Newtonian physics that show it takes a specific amount of energy to move a specific mass a certain distance. In other words, physics tells us it takes the same number of calories to move your body one mile no matter how fast you’re going.
According to science, the old school is correct. But wait…not so fast. The new school proponents believe running burns more calories per mile than walking. A recent study seems to support the new school train of thought. Researchers at Syracuse University conducted a study in December of 2004 for the purpose of comparing the energy expenditure of walking and running with equations that predict energy expenditure. As a part of the study the researchers needed to determine whether differences exist in energy expenditure of walking versus running. The researchers measured the calorie burn of 12 male and 12 female subjects as they both ran and walked for 1,600 meters on a track and a treadmill. Each subject ran at one specific pace and walked at one specific pace. The scientists, headed by Jill A. Kanaley, PhD in the Department of Exercise Science, found that men burned 124 calories when running compared with just 88 calories burned while walking. The women expended about 105 calories while running versus only 74 when walking. (Med Sci Sports Exerc, 2004 Dec;36(12):2128-34)
That seems like a big difference, but it’s actually even larger. To get the true number of calories burned from exercise, you must subtract the calories you would’ve consumed at rest. After taking away those “resting” calories, the net calorie burn for men was 105 running versus 52 walking. The net calorie burn for women was 91 running versus 43 walking. So, in reality, the subjects were burning more than twice the calories when running versus walking.
Setting the Pace
It would be nice if the answer to the calorie confusion question was that easy. But let’s take a closer look at this study. The subjects in this investigation walked and ran at only one pace. They walked at 1.41 meters per second and ran at 2.82 meters per second. At those specific paces, the subjects averaged twice the calorie burn while running. But does the result hold up for all walking and running paces? Another study showed it doesn’t.
This study was conducted by the Washington University School of Medicine for the purpose of investigating the energy expenditure and perceived exertion levels of walking and running at various speeds. The subjects each walked for five minutes at various paces ranging from four to 10.4 kilometers per hour and ran for five minutes at paces from 7.2 to 10.4 kilometers per hour. The study concluded that walking burns more calories than running at speeds greater than eight kilometers per hour (five miles per hour). The study also showed walking felt harder than running at speeds over five miles per hour.
The Mechanics of Walking Versus Running
So, who’s right? Does the old school thinking still hold up or is the new school correct? The answer is both are right!
Before you get mad at me for giving you a non-answer, please read on. Generally speaking, running does burn more calories than walking. Why? That’s a very good question with a fairly simple answer. When we walk or run, each stride results in some impact force as our lead foot strikes the ground. The mechanics of running and walking are very different. When walking we always have one foot on the ground. Our bodyweight is always supported. Each stride results in a force equaling our bodyweight being applied to our leg muscles. If you weigh 150 pounds, each stride places about 150 pounds of load on your leg. Running is very different. When running you’re completely airborne between foot plants. When your lead foot comes down, it’s absorbing more than your bodyweight due to the effects of gravity. The force placed on your leg muscles with each running stride will vary depending upon how fast you’re running. When you run faster your stride becomes longer. A longer stride equals more force with each stride. The impact for each stride will vary from 1.5 times to over four times your bodyweight, depending on your speed. It requires many more calories to absorb these much higher impact forces and to propel yourself with the next stride.
In most cases running burns more calories than walking, but when walking at increasing paces you eventually reach a point where the walking becomes more difficult than running. That point is called the “preferred walk-run transition speed” (PTS). It’s at this point walking begins to burn more calories than running.
The study from Washington University showed that this point occurs at approximately five MPH. However, this will vary slightly depending on your fitness level and how efficiently you’re walking and running. One of the predictors of running performance is running economy. This is simply a measure of how efficient you are at running. If two runners of equal fitness levels were running a race, the runner who’s the most efficient will win. This is because a more efficient runner is able to run faster with less effort. Running with less effort means you’re burning fewer calories. A more efficient runner would probably reach the walk-run transition speed at slower speeds than a less efficient runner.
How Your PTS Factors In
The bottom line is that the number of calories burned during walking and running is not a static number. It’s a dynamic measure that will increase as your speed and effort level increases. Each of us will have a preferred walk-run transition speed (PTS). Running at speeds slower than your PTS will feel harder and will burn more calories than walking. Walking at speeds faster than your PTS will feel harder and will burn more calories than running. The average PTS is about five MPH, but your individual PTS will depend on your fitness level and your walking/running efficiency. Your calorie burn per mile will increase as you accelerate at speeds faster than your PTS.
As you can see, the answer to the question of calorie confusion is that both sides are correct. There’s a point at which the calorie burn per mile of walking versus running is equal. There’s also a level at which walking burns more calories per mile than running. But, at speeds of five MPH or faster, running will burn more calories per mile than walking. It’s very difficult to estimate your exact level of calorie burn per mile without expensive laboratory analysis. In order to simplify things you’ll always get a fairly close estimate of your calorie burn by using the old accepted equation of 100 calories per mile. It won’t be exact, but it will be close and easy.