These days everybody seems to have some form of fitness tracker whether it be on their phone or smartwatch.
These trackers are useful for collecting personal fitness data like steps, distance, sleep, and heart rate. Another common feature you will most likely have access to is ‘calories burned’.
But how accurate is this measurement?
Firstly, we need to know how they come up with this info. Essentially, fitness trackers currently take information from sensors like the accelerometer, which tracks your movement.
Then they use their secret algorithms, which differ from company to company, to give you the actual, running total of calories burned i.e. energy expenditure so far that day. Based on those estimates, you might make decisions such as what to eat, drink or not eat or drink.
For instance, Fitbit has posted a (sort of) explanation of how it calculates this. It takes your personal data on age, gender, height, and weight and uses this to estimate your BMR – basal metabolic rate. It says this accounts for half the calories you burn in a day i.e. the calories you burn at rest, and that is why you will always start the day with some calories burned.
Fitbit says its calorie burn estimates are based on your personal BMR, activity tracked by your device's accelerometer and manually entered activity. This will be the basic method used by most fitness tracker makers.
But again, how accurate are they with ‘calories burned’.
A Stanford inquiry into the accuracy of seven wristband activity monitors showed that six out of seven devices measured heart rate within 5 percent. None, however, measured energy expenditure well.
An evaluation of seven devices in a diverse group of 60 volunteers showed that six of the devices measured heart rate with an error rate of less than 5 percent. The team evaluated the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and the Samsung Gear S2.
Some devices were more accurate than others, and factors such as skin colour and body mass index affected the measurements.
In contrast, none of the seven devices measured energy expenditure accurately, the study found. Even the most accurate device was off by an average of 27 percent. And the least accurate was off by 93 percent.
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