How Do Fitness Trackers Count Calories?

Let’s pretend for a while that fitness trackers’ design, comfort and ease of use don’t matter much. Let’s set the ability of the modern fitness tracker to count calories burned as first priority. Let’s find out how the dozens of fitness trackers available now, that also claim to accurately function as calorie counters, do it—and if there’s been any change since the first invention in 1977. How do fitness trackers count calories?

How does that health bracelet you have slapped on your wrist come up with all that vitals’ statistics? We find out.

Calories Burned—Background

How Do Fitness Trackers Count Calories?1. First of all, whether you are sleeping, sitting or smack in the middle of a mad sprint, you burn calories all the time. That is because you need energy released and used up to maintain vital (and not so vital) body processes. Those include breathing, digesting meals, powering brain activity, repairing injured or replacing dead body cells, and so on.

2. Second, the rate at which your body consumes energy just to maintain these processes depends on your very specific, individual traits. That rate is referred to Basal Metabolic Rate (BMR).

3. Third, BMR is pegged on your personal traits such age, height, weight, gender, physical activity, and other gene-orientated traits. And that’s how you may be losing much more weight than your exercise buddies combined or vice versa.

With that background set, fitness trackers and other calories counters shouldn’t be hard to figure out.

How Do Fitness Trackers Count Calories?

It all depends on the sensors and algorithm inside the fitness band, and the ability of the sensors to detect or miss some crucial health data or that of the algorithm to accurately analyze the data to reflect reality. Here are the ones most likely to be fit in your next (or current) fitness tracker:

1. Accelerometer

Most devices come with a tri-axis accelerometer (6-axis coming soon). This one primarily measures whether you are moving or not. It captures data regarding how fast, frequent, how long (duration), and in what direction you move.

The faster, more frequent, longer and intensive you move the higher your chances of burning the most calories. It’ll tell if you are walking or just waving a hand at a friend.

2. Altimeter

It measures elevation, altitude or depth.

Comes in handy when you want to know how hilly your jogging, etc, route is. So you can decide to charge up a more elevated track to burn more calories. This sensor also tells your fitness band how many flights of stairs you’ve been scaling, and is the backbone of any steps counter.

The more sensitive it is (together with the above two sensors), the better it is at differentiating whether you are walking briskly or jogging, and so on. Therefore, the better it’d be at calculating your energy expenditure and oxygen exchange rate—both very vital in determining how much calories your muscles are burning.

3. Gyroscope

This one combines with others (above) to measure rotation and orientation. Can help boost the accuracy of stats based on how much intensity you put into a workout.

4. Bioimpedance and Temperature Sensor

Both rarely feature in most fitness trackers but are great at measuring your skin’s resistance to electric currents and body temperature respectively.

5. Optical Sensor

Most health bands use an optical sensor to shine a green light through the wrist’s skin and into blood capillaries to determine the pressure the blood in them is flowing.

That is translated to how hard the heart is beating, hence the heart rate. T

he faster the heart beat/rate, the higher the likelihood that you are working out, and the higher the chances you have of burning more calories—compared to a slow pulse.

6. Actigraphy

It measures sleep, especially duration rather than sleep pattern and quality. Polysomnography is better at measuring the latter two. The more you sleep (quality sleep, ideally), the fewer calories you burn.

7. Algorithm

This is the software side of things. Every fitness tracker has its own software, but most have a mobile app hosting the algorithm side of the physical band.

The apps are separate from the sensors. So most bands will let you sync data collected by the sensors to the accompanying phone or tablet apps—sometimes web and other online boards. The data is then translated in “calories burned” using the algorithm.

That Accuracy Question

The more directly the armband measures the heart BEAT (not just heart rate) the more accurate your calories burned count could be. That is why app and web based calorie counters are way less accurate than health bands.

According to most researchers, including some from the National Institute of Health and Nutrition in Tokyo, Japan, in a March 2016 study published in the journal JAMA Internal Medicine, most fitness bands either overestimate or underestimate calories burned—by as much as an average of 200 calories on either side.

The team used 12 of the most popular fitness trackers on the market right now, including Fitbit’s Charge HR 2 and Flex, Jawbone’s UP 3 and UP24, Withings Pulse O2, and Misfit Shine.

Error ratings of most of the fitness bands ranged from 9.3% (BodyMedia FIT armband) to a whopping 23.5% (Nike FuelBand). Despite this, calorie counters are a great way to motivate people to exercise—through seeing real-time progress.

Bottom line

Fitness bands use a combination of sensors and algorithm to determine how much calories you’ve burned.

The more sensors packed into it, the higher your chances of capturing the most accurate data on calories burned. Interestingly, the ones with the most sensors such as the Fitbit Charge HR 2 and Jawbone UP24 (having an HRM, accelerometer, altimeter, gyroscope and laudable software analysis) comfortably outdo the rest.

So ensure you always check up on the specs list of any health bands’ package and read reviews on how the software side of each works out calories burned.

Have you ever used your fitness tracker to track your calories? How did it work out for you?

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