Step-counters, rejoice: physiologists have found that the equations used for calculating energy expenditure are inaccurate, and say we’re likely burning more calories walking than we realized. They published their report in the Journal of Applied Physiology. 

Today, most programs use one of two methods to estimate calories burned by walkers: the ACSM (for the American College of Sports Medicine) and the Pandolf, which was invented by the military. These equations are about 40 years old, which is reason enough to test them again. They were also developed using just a few adult men of average height, and if we’ve learned anything in the last few years, it’s that a small group of adult men cannot be used as a stand-in for the entire population.

So Southern Methodist University (SMU) physiologists Lindsay Ludlow and Peter Weyand decided it was time to put these formulas to the test. "Burning calories is of major importance to health, fitness and the body's physiological status," Weyand said in a press statement. "But it hasn't been really clear just how accurate the existing standards are under level conditions because previous assessments by other researchers were more limited in scope." 

The researchers built a database of existing data in the scientific literature. With this data, they could compare the ACSM, Pandolf, and other standard equations. They found that for people walking on firm, level ground, both the ACSM and Pandolf underestimated calories burned in 97 percent of the cases examined by researchers. Clearly, a new equation was in order. 

Ludlow and Weyand set out to create an algorithm that would work for anyone. "The SMU approach improves upon the existing standards by including different-sized individuals and drawing on a larger database for equation formulation," Weyand said. 

Dr. Ludlow monitors a colleague during a treadmill test. Image Credit: Hillsman Jackson, SMU

If you want to play along at home (in your ... home physiology lab), here’s what they came up with:

(VO2 is oxygen consumption and Ht is height measured in meters.)

Ludlow said their equation should apply “…regardless of the height, weight, and speed of the walker. And it’s appreciably more accurate.”  

A lot more accurate, in fact (not that that’s a high bar). The new equation is four times more accurate when used to calculate energy expenditure of a mixed group of adults and kids. For adults alone, it’s still two to three times more accurate than the old formulas. 

Accurate accounting of energy expenditure is important for more than just casual walkers. Once a person’s estimated calorie-burn rate has been established, the formula can be used to predict how much energy that person will use—and therefore how much they will need—for a certain task. Such an algorithm could be useful for athletes in training, but also for military operations, in which the need for physiological efficiency is at a premium.

"These soldiers carry incredible loadsup to 150 pounds, but they often need to be mobile to successfully carry out their missions," Weyand said. In other words, they've got to be taking in enough calories to get the job done.

As yet, the formula has only been tested for walkers on solid, flat ground. The researchers’ next step is to expand the algorithm to calculate calorie burning on hills.