More and more Germans are wearing a fitness bracelet or a smartwatch. The pedometer feature is especially popular. Smartphones can also count steps. But how does it work? And is the data reliable at all?
Fitness trackers, smartwatches and smartphones count the steps we take every day. Anyone who is aware of their health is happy to keep an eye on it, for the World Health Organization (WHO) recommends 10,000 steps a day. Depending on the device and settings, when you reach the daily goal, you will even be rewarded in the form of trophies or jumping figures on the display. It motivates you to keep moving every day. But some doubt the numbers and ask themselves the question: How reliable are pedometers at all?
The secret: the 3-axis accelerometer
The technology behind it actually consists of a so-called MEMS sensor – the abbreviation stands for “micro-electromechanical system ”. In everyday speech, this is often referred to as a 3-axis accelerometer because it can distinguish all the movements we make left, right, forward, backward, up and down. So theoretically it is able to tell if we are just turning, bending or just taking a step. The data is then evaluated and displayed in the corresponding smartphone app.
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Fitness trackers are connected to the smartphone’s navigation module
If the fitness tracker thinks it has recognized steps, it calculates the distance traveled using the stride length. To do this, some devices connect to the smartphone’s navigation module. Others, on the other hand, only calculate the step length based on the height entered by the user. However, a person’s stride length may vary. For example, fatigue or an increase may shorten it. For accurate information, smartwatches and the like should have a module to determine their position via satellite – but they usually do not.
However, it is still not possible to interpret the movements completely flawlessly. Especially fitness bracelets and watches can be easily cheated. Activities such as washing dishes or vacuuming can also be counted as a step due to the movement of the wrist. Arm movements are also interpreted as steps when dancing – even if you hardly move your legs. As a result, the pedometer values are not always reliable.
In this regard, the smartphone in the pocket seems to be more reliable because the movement of the hip is a better indicator of the movement of the whole body than the wrist. On the other hand, you do not always have your smartphone with you, it is sometimes on the desk or coffee table.
Stiftung Warentest: Eight fitness trackers detect steps accurately
Only eight of 25 tested fitness trackers were reliable as pedometers and got the rating “very good” to measure the distance. At least five others got a “good” for their pedometer function. Stiftung Warentest came to this conclusion in its 07/2020 edition. The Apple Watch Series 5 (approx. 500 euros) and Garmin Forerunner 245 (approx. 330 euros) performed best in the overall comparison. The Fitbit Inspire HR (approx. 70 euros) had the highest measurement accuracy in the test. The fitness tracker differed on average 40 percent from the actual route. In one test person, she even measured 53 percent less distance.
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FITBOOK short test: How reliable are pedometers?
For our self-experiment, we walked a few hundred meters and talked. With exactly 500 steps, it was checked how much the iPhone SE 2020 in the trouser pocket and sports watch measured on the wrist. The result: the mobile phone counted 510 steps, ie 2 percent more than it actually went. The sports watch came to the result 518, ie 3.6 percent too much. At short distances, the difference is therefore still relatively small. But if this error rate were to be maintained, the clock would already be off with 360 at 10,000 steps, and the iPhone with 200.
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How much do the values of smartphone and fitness blanket differ over a longer distance?
In another test, we also compared the pedometer on the iPhone 11 with that on the Fitbit Inspire 2 during a longer walk. The smartphone registered 6,054 steps, while the fitness tracker registered 6,423 steps on the same route, ie 369 steps more.
The pedometer should not be considered as an accurate measurement, but as a kind of guide to estimating the total physical activity in a day. Nevertheless, pedometers and related apps motivate people to take the recommended 10,000 steps a day and ultimately just move more.