Don't Get Burned by Calorie Counters

One thing everyone sweats at the gym is the question of what makes a good workout.

For those who rely on exercise machine calorie counters to determine results, the numbers might work everyone up, but they aren't necessarily working everyone out.

The Science

The University of California at San Francisco's Human Performance Center, which specializes in physiological analysis, uses a VO2 test to track fat burning down to the last calorie. The test works by measuring the maximum capacity of an individual's breathing while exercising.

The VO2 analyzer assesses a user's calories lost during exercise by tracking breathing patterns. First, the user puts on headgear similar to a scuba mask and snorkle. The snorkle is attached to a long tube that is hooked into the VO2 analyzer. Finally, the analyzer records the user's breathing pattern as he or she inhales and exhales during exercise. Depending on the quality of breathing, the VO2 analyzer calculates how hard the user is working and combines that data with the user's body stats: height, weight, age, and body fat. The VO2 analyzer can then compute how many calories are burned during the exercise.

This measurement reflects someone's fitness and can be broken down to determine how many calories one burns.

The Experiment

GMA technology contributor Becky Worley used the VO2 test on a treadmill, stationary bike, stair climber, elliptical machine and fitness watches. She used each for five minutes and, in each case, according to the VO2 test, the number of calories burned was overestimated.

On average, the machines overestimated by 19 percent and the watches overestimated by 28 percent.

Here's the breakdown:

Treadmill: Overestimated calories burnt by 13 percent. Stationary Bike: Overestimated calories burnt by 7 percent. Stair Climber: Overestimated calories burnt by 12 percent. Elliptical: overestimated calories burnt by 42 percent.

The Analysis

Joe Smith, exercise physiologist at UCSF's Human Performance Center said the overestimation is not surprising.

"I think the estimations are just that. You can't necessarily believe everything you read on those machines," Smith said.

While the calorie counters are based on VO2 data, the calculations are susceptible to many variables based on the user's height, age and body fat that could skew data, Smith said.

Manufacturers Respond

The exercise machine companies that manufactured the tested products gave additional explanations that could account for the discrepancies.

According to the makers, calorie counting software doesn't adjust to machine wear and tear. Also, machine resistance can change overtime, which skews the calculation. And none of the machines can calculate a user's metabolism rate, health history and fitness level, all of which affect calorie counters.

Maximizing the Workout

Overestimated calorie counts can also be caused by human error.

Machines can't tell if a user is leaning on the handles, which makes the workout easier. Also, an individual's body can get used to a machine and exercise, and burn fewer calories because of it.

Physiologists recommend entering a slightly lower weight to compensate for the overestimation.