Welcome to another exciting installment of Fun With Math!
Today we're going to use basic addition and subtraction to show how running is better than walking for fat loss, no matter what your doctor says. I have no idea where the myth that walking a mile burns the same number of calories as running one originated, but I do know doctors are fond of telling it. My wife — a family physician — tells me that many of her colleagues have relayed this bit of metabolic misinformation.
I see it as another example of telling people just what they want to hear: You don't have to work hard to achieve great results. Well, that's just male bovine droppings. As with most things in life, impressive results come from intense effort.
Now let's run the numbers to prove out the benefits of high-intensity exercise.
In the interest of using round numbers, let's pick a pretty big guy. A man who weighs 220 pounds is going to burn roughly 100 calories per hour sitting on the couch. That number — calories burned at rest — is referred to in exercise physiology circles as one MET (or metabolic equivalent).
According to "Essentials of Strength Training and Conditioning" (third edition), walking at a brisk pace of 4 mph burns calories at five METs. Therefore, if one MET for our test-case guy is 100 calories per hour, when he walks 4 mph for two hours at five METs per hour then he burns a total of 1,000 calories.
And this is one spot where a lot of people mess up.
Remember, he would still have burned 200 calories spending two hours on the couch, as long as he wasn't jumping up and down questioning the intelligence/coordinative abilities of his team's quarterback for throwing yet another interception. Therefore, the extra calories burned from his two-hour walk falls to 800.
One thing I should note is that because we're using a 220-pound male these caloric burns appear pretty high, far higher than what a 140-pound female would burn.
Back to our guinea pig: Let's make him run. Fast.
Say he runs 8 mph for an hour. First off, he's more efficient because he covers the same distance in half the time (giving him an extra hour to do as he pleases, such as collapse into a pile of sweaty goo and pray for death), but he also burns more calories. From the same reference above, we see that the METs for running at 8 mph are 13.5. This equates to our 220-pound dude burning 1,350 calories in one hour. Subtract the couch-sitting calories and you see he burns 1,250 extra calories, which are 450 more than the calories burned via two hours of walking.
He can also get a bit of elevated-metabolism caloric "after burn" from the intense effort, although a previous column I wrote on interval training noted that this is usually less than 10% of total calories burned.
These numbers don't just apply to running, but to any type of activity. Doing the same amount of "work" at a slow pace is not going to burn as many calories as at a faster pace, whether you're cycling, swimming, paddling or crawling on all fours.
And there is more to it than math. Which means we now have to bust another myth — that you should train in the "fat-burning zone."
Perhaps you've seen those charts on aerobic equipment that lay out "cardio training zones" and "fat-burning zones." These charts show that fat-burning takes place during moderate effort, when your heart rate is at about 65% of maximum, and that cardio training kicks in when heart rate climbs above 75%. You know, the point where your lungs start burning like when wasabi goes down the wrong tube.
Numerous research studies and exercise physiology texts agree that the human body primarily uses fat stores as a source of fuel at moderate intensities — say, running at 6 mph with a heart rate at 65% — and switches to using stored carbohydrates as a source of fuel as exercise intensity climbs until, at the highest intensities, more than 90% of the energy required comes from those carbohydrate stores.
But this doesn't mean that exercising moderately burns more fat over the long haul than high-intensity training. In fact, quite the opposite is true.
Weight loss comes down to sustaining a caloric deficit. And, as shown above, sustaining higher intensity exercise burns more calories. Therefore — dietary intake being equal — exercising at higher intensities is going to allow you to generate larger caloric deficits, leading to additional weight loss.
And if you're being smart and including some resistance training in your fitness regimen, you can ensure that all this weight loss comes from fat stores.
See, if you're in a caloric deficit over time, the type of energy stores — fat or carb — you're using during exercise is irrelevant. Your body is going to engage in fat-burning whether you are exercising or not. You could be sleeping, doing your taxes or watching videos of honey badgers on YouTube and fat is still going to burn.
And there is evidence, in any case, that higher-intensity exercisers achieve more fat loss. Researchers from the department of exercise physiology at West Virginia University compared high-intensity and low-intensity training in a small study of 15 women ages 18 to 34. Their findings, reported in 1997 in the Journal of the American College of Nutrition, showed that after 11 weeks the members of the high-intensity group lost approximately 5% of their body fat, while the low-intensity group didn't lose any.
An important note in all of this is that you want to maximize total caloric burn. Don't exercise at such a high intensity that your overall volume of training is significantly shortened. You can only push it to the wall for so long, so pick a pace that is difficult yet doesn't make you hate life so much that you can't keep it up.
My final plug for pushing limits and finding a sustainable level of high-intensity exercise comes from personal experience: Through my many years of running and cycling, I've noticed that the faster people are the leaner ones. I think when we push ourselves to go fast we adopt a general life attitude of posterior-kickery that leads to even more time spent exercising and improves the ability to make wise dietary choices and achieve the challenging goal of sustaining a healthy body fat percentage.
Which doesn't mean you should charge out the door and sprint until you hack alveoli; no one becomes hard-core overnight. Do what you can handle, but continuously push your intensity comfort zone in increments.
Baby steps can make you fast.
Fell is a certified strength and conditioning specialist in Calgary, Canada.