This is the first post in a series covering common fitness myths.
Although the title mentions walking and running, this is really a post about exercise intensity in general. There’s a common misconception among exercisers that a body will burn the same number of calories when covering a given distance regardless of pace. But the truth is that whether you’re walking/running a mile, swimming 20 laps or bicycling to the grocery store and back, you’ll actually burn more calories over that fixed distance if you cover it faster.
The rationale behind the myth goes something like this: When you move more slowly – walking a mile rather than running it, for example – it takes you longer to cover the same distance, so even though you’re burning fewer calories per minute, you’re exercising for more total minutes, so the total calories burned must be about the same, right? Wrong! The fact is, the relationship between exercise intensity and duration is not a linear one. Your total calorie burn increases more with an increase in effort than it does with an increase in time. It’s silly to think that the rate of energy expended with varying effort levels would magically correspond to units of time.
This fact is actually more pronounced with walking/running than with swimming or cycling. With swimming or cycling, you’re basically doing the same motion, only faster, but running involves significantly different body mechanics than walking does. When you walk, one foot is always on the ground, albeit for a very short amount of time. When you pick up the pace and start to jog, though, each and every stride includes something called a swing phase or recovery phase, where your entire body is suspended in the air. A split second before that mid-air flight comes the propulsion phase, where your body has to use considerable energy to become airborne. This propulsion is what makes running so much more energy-demanding than walking.
Regardless of which mode of exercise you consider, though, there’s another factor at play that most proponents of this myth never even think of – net versus gross calorie expenditure. Here is where higher intensity blows lighter effort out of the water!
Say you’re going to travel one mile on foot, and let’s pretend you weigh 150 pounds. You decide to walk that mile at a good moderate pace of 3.5 miles per hour. It takes you 17.5 minutes to cover that mile and you burn about 77 calories doing it. Oh, but if you had been sitting on the couch for 17.5 minutes, you would have burned about 21 calories anyway, so your net exercise calories for walking one mile at 3.5 MPH is 56 calories.
Now let’s say you decide to jog that same mile at an easy pace of 5.0 MPH. It only takes you 12 minutes to cover the distance, but you burn 124 calories. During those 12 minutes, if you had been sitting on the couch, you would have burned 14 calories anyway, so your net calorie burn for jogging one mile at 5.0 MPH is 110 calories.
Now there’s already a pretty big difference in gross calories between walking and jogging that mile – 61%, but the difference in net calories – 56 walking and 110 jogging – is a whopping 97% increase!
The beautiful thing about this fact i that it holds true regardless of what type of exercise you’re doing. Even among different walking speeds, your net calories expended over a given distance goes up as you increase your pace. So the next time you hit the bike path or the lap pool or the treadmill, step up the intensity a bit. You’ll get done with your workout faster and burn more calories in the process!
(Metabolic calculator at ExRx.net used for the above examples.)