Hey, it’s Robert Davis, the Healthy Skeptic.

Wearable fitness trackers and many cardio machines show us how many calories we burn during exercise.  So how believable are the numbers?

In a study of seven fitness trackers used for walking, running, and cycling, all had error rates of over 25%. One was off by more than 90%.

Cardio machines aren’t much better.  Some let you enter your age and weight, which improve accuracy.

But the machines don’t take into account other factors that affect calorie burning, including:

Body composition – people with a higher percentage of muscle expend more calories.

Fitness level – beginners may burn more because their movements tend to be less efficient.

And form – gripping the handrails on a treadmill, for example, can reduce calorie burning.

Overall, cardio machines can be off by 20 percent or more, with ellipticals especially likely to have readings that are too high.

Still, calorie counts from machines and trackers may be helpful by showing trends in your workouts. An increase from one day to another for the same activity can indicate you’re working harder…. And motivate you to keep moving.

For the truth about more fitness-related claims, check out my book, Fitter Faster. You’ll also learn how to slash your workout time and get even better results.