In a recent study, researchers found that the data reported by 7 commonly worn fitness devices are incredibly inaccurate, especially energy expenditure (number of calories burned). Since millions of people wear these devices, and are potentially using them to help inform healthy decisions, this is important news. These are devices that typically measure heart rate, metabolic rate (calories burned), steps and other activity amounts, and maybe oxygenation of blood. The heart rate is usually fairly consistent and accurate across the devices tested, but the metabolic rate – which is what would help you justify eating a bowl of ice cream for lunch, can be off by as much as 93%.

Popular Devices Used in Testing

The specific devices assessed were: Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and the Samsung Gear S2. The amount that the devices were off ranged from 27% inaccurate to 93%. The manufacturers of these devices are not held to the same standards as manufacturers of medical grade equipment – because basically they are toys. But they are not being used as toys, and many individuals are using them to make important dietary and health decisions.

Testing the Devices

To test the devices, 31 women and 29 men wore the 7 devices while undergoing a variety of different cardiovascular workouts. Each volunteer’s heart rate was measured with a medical-grade electrocardiograph and their metabolic rate was estimated with indirect calorimetry and compared to the worn fitness tracker. The heart rate was surprisingly accurate, deviating an average of only about 5%. The metabolic rates on the other hand, were a different story. The reason for the poor accuracy is that measuring metabolic rate is done through an algorithm which is different for each device. The algorithm makes certain assumptions when making its final calculations, which may or may not be true of the person its measuring. It is difficult to make an indirect measurement this way, and have it be consistent over a large population.

Source

1. Shcherbina A, Mattsson CM, Waggott D, et al. Accuracy in Wrist-Worn, Sensor-Based Measurements of Heart Rate and Energy Expenditure in a Diverse Cohort. J Pers Med. 2017;7(2)

Node Smith, associate editor for NDNR, is a fifth year naturopathic medical student at NUNM, where he has been instrumental in maintaining a firm connection to the philosophy and heritage of naturopathic medicine amongst the next generation of docs. He helped found the first multi-generational experiential retreat, which brings elders, alumni, and students together for a weekend campout where naturopathic medicine and medical philosophy are experienced in nature. Three years ago he helped found the non-profit, Association for Naturopathic ReVitalization (ANR), for which he serves as the board chairman. ANR has a mission to inspire health practitioners to embody the naturopathic principles through experiential education. Node also has a firm belief that the next era of naturopathic medicine will see a resurgence of in-patient facilities which use fasting, earthing, hydrotherapy and homeopathy to bring people back from chronic diseases of modern living; he is involved in numerous conversations and projects to bring about this vision.