Figuring out the answer involves a fairly straightforward calculation, but the overall equation is not as simple as it seems.
Figuring out how many calories you burn when running is, on a simple level, a fairly straightforward calculation. Most experts (and lots of studies) suggest that a person of average weight burns about 100 calories in a mile of running. That number goes up slightly if you weigh more or if you’re a less efficient runner—both of which require that you use more energy to cover the same distance. On the contrary, that number of calories doesn’t go up if you run faster.
“It doesn’t matter how fast you go,” says Dr. David Swain, a professor of exercise science and the director of the Wellness Institute and Research Center at Old Dominion University. The amount of calories burned over a mile still remains roughly the same.
Generally speaking, of course, if you run faster you’ll cover more miles in the same amount of time, which equals more calories burned in that time. Think about it: A person running 10-minute miles for an hour covers six miles and burns about 600 calories in this calculation; a person running 6-minute miles for that same amount of time runs 10 miles and burns 1,000 calories.
“It’s a basic metabolic equation,” says Craig Broeder, CEO of Exercising Nutritionally and a research scholar chair in exercise science at Northern Illinois University. For every liter of oxygen you consume, you burn about five calories.
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A calorie is defined as the amount of energy used to raise the temperature of one gram of water one degree. In fact, calories used to be determined by measuring how much a person inside a calorimetry chamber warmed the water surrounding them. Over many studies, it was determined that there was a direct relation between the amount of oxygen the person in that chamber consumed and the amount of calories burned. That, then, saves researchers a lot of effort and now they simply measure the amount of oxygen a person consumes, and the carbon dioxide they produce.
Technically, though, when it comes to exercise and food, what we refer to as a calorie is really a kilocalorie (equal to 1,000 calories). The problem is that textbooks used to refer to kilocalories by denoting them as Calories, with a capital C. Eventually, Americans just started referring to them as calories and now almost all Americans call them calories, instead of kilocalories.
“Of course, it’s ridiculous,” says Swain. “We’re the only country in the world that does it.”
Really, then, the simple answer is that you burn about 100 kilocalories per mile of running—which Americans often refer to as calories—and that number will vary depending on your size, efficiency and individual differences. That 100 kilocalories is actually net energy burn, or the amount of energy over your baseline metabolism, since we’re always burning calories, even when we’re just sitting.
Of course, there’s a more complicated answer too.
The calories-per-mile rule of thumb changes slightly for walking. A study done by researchers at Syracuse found that men burned about 105 kilocalories/mile on average running a mile in 9 minutes and 30 seconds, and about 52 calories when walking the same mile in 19 minutes. For the women in the study, that burn was 91 and 43 calories, respectively.
“Walking is entirely different,” says Swain. “They’re two different modes of movement.”
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Running technically involves jumping from foot to foot to propel yourself forward, while both feet never leave the ground in walking. Obviously, there is a crossover at points of very fast walking and very slow running. In fact, some studies suggest that walking faster than 12-minute miles actually burns more calories than running a 12-minute mile.
The extra complicating factor is that, although the amount of calories you burn per mile doesn’t change fundamentally whether you’re running fast or slow, the amount of calories you burn in the aftermath does change.
“The person who ran the mile faster will always have a greater residual calorie expenditure,” explains Broeder.
You are always burning a base level of calories, even at a resting state. After running fast, your heart rate is elevated and you’re breathing hard. You’re not at a resting state, and so you’re burning more calories than you would otherwise. That’s less the case after running a slow mile.
“You don’t instantaneously return to a resting state,” says Swain.
One study, Broeder says, suggests that if you burn 720 calories running at 80 percent of your VO2 max, as opposed to burning 720 calories running slower at 60 percent of your VO2max, your base rate of calorie burning will be elevated by 15-25 percent for up to 24 hours. Other studies have been less conclusive in the number, but consistently find that more intense exercise leads to a greater after-burn effect.
However, if your goal is to burn calories or lose weight, you have to weigh the options. Generally, a non-elite runner can only do a really intense running workout maybe once or twice a week at risk of getting injured from the higher intensity. Or, you risk burning out and not being able to do as much running, which then actually burns less calories.
“It’s a trade-off,” Broeder says.
So, how many calories does running burn? It’s not as simple as it seems.