May 3, 2025, 12:18 pm | Read time: 3 minutes
Whether it’s heart rate, pace, or distance, wearables promise a wealth of data for fitness enthusiasts. However, a recent study reveals that these measurements are not always as accurate as many believe. Significant weaknesses are particularly evident in heart rate monitoring and swimming.
A study by researchers from Magdeburg and Leipzig reveals how accurately ten current smartwatches and fitness trackers measure during sports activities, with some significant deviations in heart rate, distance, and swimming style. One model stands out positively.
What Wearables Can Do — and Where Their Weaknesses Lie
Smartwatches and fitness bands accompany many people during sports. They are intended to help monitor performance and health — from heart rate to running speed to swimming distance. But how accurately do these devices actually measure?
A research team from the Magdeburg-Stendal University of Applied Sciences and the Institute for Applied Training Science Leipzig, led by Prof. Olaf Ueberschär, investigated this question. In their study, they tested ten different wearables with 30 test subjects — including amateur and semi-professional athletes — while running, cycling, and swimming.
Heart Rate Often Inaccurate — Even with Good Devices
A central finding of the study concerns heart rate measurement. This was compared with an ECG-validated chest strap. It was found that many wearables provide inaccurate values, especially when running on a treadmill.
The researchers cited differences in subcutaneous fat tissue, skin color, and movements between the watch and skin as possible causes. Notably, the Apple Watch SE was closest to the actual values, yet it still detected 40 extra heartbeats in two athletes.
To measure the accuracy of smartwatches or fitness trackers, testers recorded their heart rate with an ECG or chest strap before exercising. The values were then compared with those from the smartwatch.
Distance Measurement While Running Mostly Accurate — Problematic While Swimming
While running, modern GPS and GNSS sensors proved largely reliable. The average deviation from the actual distance was about 5 percent, with peak values ranging from just 0.8 percent to a maximum of 17 percent. The most accurate devices were the Garmin Forerunner 955 Solar, the Huawei Watch GT 3, and again the Apple Watch SE, all staying below the one-percent mark.
On the bike, the measurements were even more precise — especially on longer routes with few curves. The stability of the movement seems to contribute to better measurement accuracy here.
The picture is quite different when swimming: The study shows that all tested devices failed to accurately detect distance or style in varying swimming strokes in the pool.
However, there were exceptions on standardized test tracks. Three products demonstrated fairly good measurement capability while swimming — at least in a 400-meter freestyle. Here, Garmin again performed best. The Polar Ignite 2 and the Fitbit Versa 4 also came relatively close to the actual distance, with only one lane deviation.
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Smartwatches and Fitness Trackers Not Always Accurate in Sports
Wearables offer many helpful functions in everyday life and training, but their accuracy in measurement is highly dependent on the area of use. While distances in running or cycling are reliably recorded, heart rate data and swimming analyses are often unreliable. Those who want to accurately track their performance should, therefore, also rely on proven measurement instruments like chest straps.