What is it about?

Fitness trackers are a relatively new trend and many people are trying to understand more about their health, performance and wellbeing. These trackers are often used to track activities such as steps and calories burnt. However, newer trackers are also able to measure heart-rate right from your wrist. They do this by shining light into your skin, collecting the light that was not absorbed by the blood and using this information to estimate how hard your heart is pumping. This sounds all pretty simple but the key question is how accurate the heart rates are that these trackers measure. Also, while many researchers have checked this in a laboratory environment where a lot of things can be controlled, real-life accuracy has rarely been assessed.

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Why is it important?

This work is important as it is the first in which heart-rate measures of wrist-worn trackers have been assessed comprehensively in the lab and real-life. The implications of our research are that heart-rate measures of trackers are reasonably trustworthy at lower activity intensity levels. However, many campaigns and also the World Health Organization encourages that people should accumulate more intense physical activity. Using a tracker to monitor such activities might be problematic.


We conducted a study with 55 people who wore an expensive and a less expensive wrist tracker during a cycling exercise and normal life. They also wore a chest-strapped heart-rate monitor that measures heart-rate very accurately. These three devices measured heart rate every 1 to 10 seconds. After we collected all this data we checked how well the tracker data matched the data from the chest device. Overall, the expensive tracker did very well during the cycling exercise and also in real life. It showed very small errors (well below 10%) and 'agreed' very well with the chest-strap data. The less expensive tracker also did reasonably well; this was especially so in real life where the error was just above 10% and agreement was higher. What was probably most insightful was that the trackers, especially the less expensive one, were less accurate at higher movement intensities. As such, we can assume that overall the trackers capture heart rate quite well during normal low intensity activities such as walking, while they perform less well when we increase our activity levels (e.g., during hard exercise).

Dr Andre Matthias Müller
National University of Singapore

Read the Original

This page is a summary of: Validity of heart-rate measures from wrist-worn activity trackers in a laboratory and free-living setting (Preprint), JMIR mhealth and uhealth, March 2019, JMIR Publications Inc.,
DOI: 10.2196/14120.
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