More and more Germans wear a fitness bracelet or a smartwatch. The pedometer function is particularly 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 pays attention to their health likes to keep an eye on it, because the World Health Organization (WHO) recommends 10,000 steps per day. Depending on the device and settings, when you reach the daily goal, you are even rewarded in the form of trophies or jumping figures on the display. That motivates you to keep moving every day. But quite a few doubt the numbers and ask themselves the question: How reliable are pedometers anyway?
The secret: the 3-axis accelerometer
The technology behind it actually consists of a so-called MEMS sensor – the abbreviation stands for «micro-electro-mechanical system”. Colloquially, 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’s able to tell if we’re just turning, bending, or just taking a step. The data is then evaluated and displayed in the associated smartphone app.
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Fitness trackers connect to the smartphone’s navigation module
If the fitness tracker thinks it has recognized steps, it calculates the distance covered using the step length. To do this, some devices connect to the navigation module of the smartphone. Others, on the other hand, only calculate the step length from the height entered by the user. However, a person’s stride length can vary. For example, exhaustion or an increase can shorten it. For precise information, smartwatches and the like would have to have a module for determining their position via satellite – but they usually don’t have that.
However, it is still not possible to interpret the movements absolutely error-free. Fitness bracelets and watches in particular can be easily fooled. 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 respect, 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 don’t always have your smartphone with you, it’s sometimes on the desk or coffee table.
Stiftung Warentest: Eight fitness trackers record steps precisely
Only eight of 25 fitness trackers tested were reliable as step counters and received the rating «very good» for measuring the distance. At least five others got a “good” for their pedometer function. Stiftung Warentest came to this conclusion in its 07/2020 issue. The Apple Watch Series 5 (approx. 500 euros) and the Garmin Forerunner 245 (approx. 330 euros) performed best in the overall comparison. The Fitbit Inspire HR (approx. 70 euros) had the greatest measurement inaccuracies in the test. The fitness tracker deviated from the actual route by an average of 40 percent. 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 counted. With exactly 500 steps, it was checked how much the iPhone SE 2020 in the trouser pocket and the sports watch measured on the wrist. The result: the cell phone counted 510 steps, ie 2 percent more than actually walked. The sports watch came to the result 518, i.e. 3.6 percent too much. The difference is therefore still relatively small over short distances. However, if this error rate were to be maintained, the clock would already be off by 360 at 10,000 steps, and the iPhone by 200.
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How much do the values of smartphone and fitness rug differ over a longer distance?
In another test, we also compared the pedometer of the iPhone 11 with that of the Fitbit Inspire 2 during a longer walk. The smartphone recorded 6,054 steps, while the fitness tracker recorded 6,423 steps on the same route, i.e. 369 steps more.
Photo evidence No.1: The smartphone app measured 6054 steps Photo: Private Photo evidence 2: The fitness tracker counted 6425 steps Photo: Private
Conclusion
The pedometer should not be regarded as an exact measurement, but as a kind of guide for estimating the total physical activity of a day. Nevertheless, pedometers and related apps motivate people to take the recommended 10,000 steps a day and ultimately just move more.