A new paper published in JAMA Internal Medicine shows that these devices are not even correctly performing their most basic function, which is accurately measuring physical activity and estimating energy expenditure.Researchers in Japan compared 12 wearable fitness devices, including the popular Fitbit and Jawbone devices, with two "gold standard" research techniques, the metabolic chamber method, which captured all metabolic activity in a 24-hour period, and the doubly-labeled water (DLW) method, which captured metabolic activity in a real-life setting over 15 days. The 19 healthy adults participating wore all 12 devices while undergoing the two gold standard methods. The devices and methods were then used to calculate energy expenditure.
They concluded that their findings "suggest that most wearable devices do not produce a valid measure of total energy expenditure."The findings might shock and disappoint the large number of people who have bought these devices. In 2015, according to the Times, the market for wearables doubled from the year before to reach $1.5 billion. Many think this is just the start, with at least one analyst predicting an astonishing $50 billion in sales in just a few years.
But the results of the study almost certainly won't shock researchers in the field who have spent a lot of time trying to measure exercise and energy expenditure. Michael Joyner, MD, of the Mayo Clinic in Rochester, Minn., noted that these experts have expressed "concern for several decades or more about wearables that rely primarily on accelerometers," which is the underlying technology behind the mobile fitness trackers used in the study. Even devices that have been "validated" for use in research were not particularly reliable in the study.
Joyner further noted that the differences between the devices is also "troubling," and that this problem will likely "get worse when more heterogeneous groups are assessed." In other words, as devices are used by more and more people belonging to populations for whom the devices have not been designed, the results will become even more unreliable.
The new study is only the latest to turn up disappointing results for mobile health devices and apps. Earlier this month a paper in JAMA Internal Medicine showed that a best-selling blood pressure app for mobile phones delivered completely unreliable results. Also recently, the first prospective randomized trial in the field, led by Eric Topol, MD, of the Scripps Translational Science Institute in La Jolla, Calif., found no health benefits in people using smartphones to monitor blood pressure, diabetes, and arrhythmias.