The Accuracy of Calories Burned in Polar Heart Rate Monitors

Polar Heart Rate Monitors: Chest Straps vs. Wrist-Worn Watches

If you're looking for a wearable heart rate tracker that's readily available to consumers, you can hardly do better than a chest-strap heart rate monitor from Polar. Many of these models have been clinically validated for their accuracy, to the point that they're often used as the baseline for monitoring heart rate activity in clinical studies.

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Two of the best ways to be sure you're getting a clinically validated Polar heart rate monitor — which is especially important if you're wearing a heart rate monitor for medical reasons, but also guarantees better accuracy if you're tracking your heart rate to measure exercise intensity — are to talk to your doctor or to search the PubMed database for clinical trials validating your particular model of Polar heart rate monitor.

What About the Accuracy of Calories Burned?

There's always a catch. Here, it's that measuring your exercise intensity (in this case, according to heart rate) is just one of many factors that goes into estimating how many calories you've burned. And as Stanford researchers reported in a May 2017 issue of the ​Journal of Personalized Medicine​, even good accuracy from a heart rate monitor doesn't always correlate to accurate calorie-burn estimates.

The researchers evaluated seven fitness-tracking devices with the help of a small group of 60 volunteers and found that six of the devices were accurate for heart rate to within 5 percent.

None of the devices were from the Polar brand, but the findings are still helpful for understanding that even when heart rate accuracy was good, the accuracy of measuring energy expenditure, or calories burned, was not: The most accurate device was off by 27 percent, and the least accurate was off by a staggering 93 percent.

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Researchers explained that for the lay user in a nonmedical setting, the ideal error rate for gauging energy expenditure is less than 10 percent.

How Do Polar Watches Fare at Tracking Calories Burned?

As the ​Journal of Personalized Medicine​ study demonstrated, accuracy of heart rate monitoring doesn't necessarily correlate with accuracy of measuring energy expenditure, which is really what "calories burned" represents. But with Polar heart rate monitors so often functioning as the gold standard for measuring heart rate, is it possible that Polar fares better at being a calorie-counter watch?

What the Research Says About Polar Heart Rate Monitors and Calories Burned

Like the other fitness tracking device used in the test, the Polar S810i heart rate monitor was shown to significantly overestimate energy expenditure during low-intensity exercise. However, there was no significant difference between the Polar results and the indirect calorimetry results at moderate exertion levels, and the overall results still correlated well at low intensities.

Overall, the researchers decided that despite the variability at low intensities, results correlated well enough for the Polar heart rate monitor to provide accurate calories burned estimates. But they went on to note that for that to be true, the heart rate monitor had to be programmed with the exerciser's measured VO2max (a measurement of your body's ability to uptake oxygen) and maximum heart rate, as opposed to the estimated values you typically have access to outside a clinical setting.

Ultimately, Polar heart monitors aren't as accurate for measuring calorie expenditure as they are at tracking your heart rate. However, even if the numbers you get aren't 100 percent accurate, they might still be useful for goal-setting purposes and tracking your relative progress and workout intensity — i.e., whether the overall amount of energy you expend is trending up or down.