A small study suggests that fitness trackers are not a reliable method to measure how hard you work out. The research reveal that the devices are very good at measuring heart rate while you rest, but they give conflicting readings when it comes to heart rate during exercise.
Researchers tested four brands of fitness trackers which use a LED to track the heart rate through the changes in blood volume observed through the skin. Study volunteers were asked to wear a wristband on each wrist and compare the readings while exercising and while at rest.
Researchers later compared the results to an electrocardiogram (ECG) test, which is the method used by health professionals for years to monitor heart rate.
The trial revealed that the Fitbit Surge was the best at measuring the heart rate while the users were resting. The Basis Peak fared the worst in this category. When it comes to exercise heart rate, none of the trackers – which included the Mio Fuse and Fitbit Charge – matched the readings of an ECG machine.
Study authors believe the fitness trackers are not accurate enough to help patients with heart problems detect their medical conditions. Lead author Lisa Cadmus-Bertram said that the tracker is accurate “at most moments,” but it can sometimes be off by a fair bit.
So, the study authors do not recommend the trackers for medical applications during exercise. Researchers recommend the devices to be used only for recreational purposes as they can be “useful and motivational.”
The study may have some limitations due to its small sample size. It has also only limited repeatability for the same volunteer under particular conditions. Yet, the study revealed the limited medical applicability of the fitness devices.
Doctors recommend patients with conditions that affect the heart rate such as atrial fibrillation and heart failure not to rely on fitness trackers to detect abnormal heart rhythms especially during physical activity.