Not All "Walking Calories" Are Equal

By Jane Farrell

Walking is the most common exercise, and many walkers like to count how many calories are burned. But they may not be fight.

It’s a little-known fact that the leading standardized equations used to predict or estimate walking energy expenditure — the number of calories burned — assume that one size fits all. The equations have been in place for close to half a century and were based on data from a limited number of people.

A new study at Southern Methodist University, Dallas, found that under firm, level ground conditions, the leading standards are relatively inaccurate and have significant bias, A new standardized equation developed by SMU scientists is about four times more accurate for adults and kids together, and about two to three times more accurate for adults only, Ludlow said.

“Our new equation is formulated to apply regardless of the height, weight and speed of the walker,” said Ludlow, a researcher in the SMU Locomotor Performance Laboratory of biomechanics expert Peter Weyand. “And it’s appreciably more accurate.”

Ludlow and her colleagues report the new equation in the Journal of Applied Physiology.

“The economy of level walking is a lot like shipping packages – there is an economy of scale,” said Weyand, a co-author on the paper. “Big people get better gas mileage when fuel economy is expressed on a per-pound basis.”

The SMU equation predicts the calories burned as a person walks on a firm, level surface. Ongoing research is expanding the algorithm to predict the calories burned while walking up- and downhill, and while carrying loads, Ludlow said.

The research comes at a time when greater accuracy combined with mobile technology, such as wearable sensors like Fitbit, is increasingly being used in real time to monitor the body’s status. The researchers note that some devices use the old standardized equations, while others use a different method to estimate the calories burned.