Walking and running are widely used modes of exercise to improve fitness and promote weight loss. The energy expended (calories burned) during walking or running can be directly measured in a lab or estimated based on speed and body weight. It can also be determined using one of many wearable devices and mobile apps. A commonly used estimation is that walking or running one mile elicits an energy expenditure of 100 calories.
This estimation, while crude, is interesting because of its wide use and apparent acceptance, even though it hasn’t been tested for accuracy. Research we did in the Exercise Science Lab at USC Aiken and presented at the American College of Sports Medicine annual meeting last week examined the accuracy of the 100 calories per mile estimate across a wide range of walking and running speeds. This is the topic of my Health & Fitness column in the Aiken Standard this week
To do this we asked subjects ranging in age from 20 to 44 years to walk or run one mile at a speed they selected on a treadmill while energy expenditure was determined. Some of the subjects walked and some ran, so the speeds ranged from 3 to 7 mph. For accuracy, we measured the air they breathed to measure how much oxygen they consumed to calculate how many calories they burned.
We found that the measured energy expenditure across all speeds was 108 calories per mile. It was higher (115 calories) during running and lower (98 calories) during walking. None of these were significantly different from the 100 calories per mile estimate.
There was a high degree of variability among subjects in energy expenditure, even at similar walking or running speed. This was due to body weight, with heavier people burning more calories when they walked or ran.
These findings are consistent with previous studies that compared the measured energy expenditure of walking and running one mile at set speeds. In our study, we allowed subjects to select their own walking or running speed, so it more closely reflects how people would exercise outside of a research setting. Research also shows that the energy expenditure during treadmill exercise was almost exactly the same as walking or running on a track, so our findings would also be applicable to walking or running on level ground.
In conclusion, the widely used estimate of 100 calories per mile appears to be accurate across a wide range of walking and running speeds. This supports using the 100 calories per mile value for estimating energy expenditure for fitness or weight loss purposes. For example, some exercise programs prescribe exercise based on calories burned rather than time or distance. And people who are trying to lose or maintain weight can use the 100 calories per mile estimate to help balance their energy intake and expenditure.
It is important to note that the 100 calories per mile estimate does not replace more accurate measurements or calculations that are done in a research or clinical setting. And wearable devices and apps are easy ways to get a good idea of how your energy expenditure during a wider range of activities. But, if you want to know how many calories you burn during a run or how long you need to walk to offset what you eat, the 100 calories per mile estimate will give you a pretty good idea.