How Do Fitness Trackers Calculate Calories Burned?

There are several things a fitness tracker can do and one of its most popular features is its ability to calculate calories burned.

Interestingly, the technology employed in producing this function is not known to many users of this device.

Understanding how your wearable works in burning your calories is something you should know as it can help you ascertain if the value you’re seeing on the device is accurate.

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Usually, calories are burned primarily through digestion; and maintaining basic body functions and physical activity.

Basically, the tracker works by taking information from sensors like the accelerometer which tracks your movement. However, this is not all that there is to it when measuring the calories burned

The device also makes use of your personal data such as age, gender, height and weight to make estimations on your basal metabolic rate (BMR).

The BMR accounts for half of the calories you burn in a day. It is the calories you burn at rest. This explains why you often see a value on calories burned on your device when you wake up in the morning.

Overall, your calorie burn estimates are based on your BMR, activity tracked by your device’s accelerometer and the manually entered activity. This is the basic method used by most fitness tracker makers.

Also, trackers make use of other data points such as workout length, workout type, your baseline fitness level, muscle groups used, muscle content. If you’re exercising, it also takes in to account the resistance and amount of weight being lifted.

Other data points that you device may use include your heart rate and metrics like perspiration.

If you’re looking to estimate the accuracy of your fitness tracker, you can use a metric called MET which is defined as the ratio for calories burned per hour when you’re at work (walking, running, chopping wood, washing dishes, etc.) to your resting metabolic rate (when you’re sitting or sleeping).

The principle behind MET is that every activity has its own value and this is what is used in the calculation to determine how many calories you’re actually burning.

Although, fitness trackers use specific algorithms to estimate energy expenditure (calorie burn), you can still compare its accuracy using the MET value.

For example, sitting has a value of one MET, meaning that you burn 1 calorie per kilogram of weight per hour.  So if you weigh 145 pounds (about 66kg), you burn at rest 66 calories per hour.  Other activities like walking and jogging will certainly have a higher MET value than 1 because you’re expending more energy to perform the activity than when you’re just sitting still.

You can compare your burned calorie to what your tracker provides if you know the MET value for whatever particular activity you’re doing.

This is done by inputing the MET value into the following equation.

MET value * weight in kg = calories burned per hour.

You can find out the MET value for different activities by visiting the Activity Categories of the Compendium of Physical Activities site.

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